Folate mediates cognitive impairment of aged people with periodontitis

doi:10.21203/rs.3.rs-3967077/v1

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Research Article

Folate mediates cognitive impairment of aged people with periodontitis

https://doi.org/10.21203/rs.3.rs-3967077/v1

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Aims

To examine the mediation of folate on the periodontitis-promoted cognitive impairment (CI) in the elderly population.

Materials and Methods

Data for this cross-sectional population-based study was obtained from the National Health and Nutrition Examination Survey (NHANES), 2011–2014 database. Associations between periodontitis and cognitive scores, exogenous and endogenous folate levels were estimated by propensity score weighted regression models. Natural effect models were applied to estimate the mediation effect of folate for the periodontitis-cognition relationship.

Results

Out of the 1966 participants, 869 (44.2%) had periodontitis. The periodontitis group has lower cognitive scores and dietary supplement, serum total, and RBC folate levels. The mediation effect of dietary supplement folate for periodontitis-general cognition score association was significant with mediation proportions of 8.4%. The mediation effects of serum total folate and RBC folate for periodontitis-general cognition score were both significant with mediation proportions of 9.1%. Notably, periodontitis cases with dietary supplement folate or high dietary intake folate had significantly higher general cognition scores than those of periodontitis cases without dietary supplement folate or with low dietary intake folate.

Conclusions

Exogenous folate supplementation can alleviate periodontitis-related CI in the elderly population. Serum and RBC folate are key markers for alleviating periodontitis-related CI.

folate

periodontal disease

cognitive function

Alzheimer's disease

causal inference

Scientific Rational for Study: It remains unclear whether exogenous and endogenous folate play crucial roles in periodontitis-promoted CI in the elderly population.

Principal Findings: Dietary supplement, serum total, and RBC folate levels mediated the periodontitis and CI association. Besides, periodontitis cases with dietary supplement folate or higher dietary intake folate had lower odds of CI.

Practical Implications: It is meaningful for the elderly population with periodontitis to take dietary supplement folate or consume foods rich in folate to prevent CI.

Alzheimer's disease (AD) and other types of dementia, characterized by progressive memory loss and cognitive impairment (CI), is a global debilitating disorder, with more than 50 million people currently and an expected global prevalence of 150 million by 2050 [1, 2]. However, there are still no effective treatments for AD, which places a huge socioeconomic burden on patients and healthcare systems [3]. Therefore, it is crucial to gain a deeper understanding of the modifiable risk factors and underlying mechanisms that contribute to CI, in addition to the natural process of aging, so that novel effective preventive measures can be developed.

Periodontitis, a chronic inflammatory disease triggered by an imbalance in the oral microbial community in a susceptible individual, is one of the most widespread diseases, affecting approximately 42% of US adults and 50% of the global population [4, 5]. Recently, emerging evidence supports that periodontitis is a crucial risk factor for CI and AD among the elderly population (≥ 60 years) [5–8]. For instance, a retrospective cohort study has reported that periodontal diseases are associated with an increased risk of all-cause dementia [9]. Besides, a prospective cohort study has indicated that having more teeth is associated with a faster rate of hippocampal atrophy (one of the main clinical manifestations of AD) in community-dwelling individuals with severe periodontitis [10]. Although the association between periodontitis and CI has been well-known, the underlying mechanisms are not fully understood.

Folate plays an important role in the maintenance of normal neurological functions such as memory and learning function [11]. Notably, basic research has suggested that folate supplementation can improve CI associated with lithium administration during pregnancy in rat offspring [12]. Besides, folate deficiency is reported to increase microglial amyloid-β phagocytosis (one characteristic of AD pathological features) [13]. These findings indicate that the level of folate in humans is associated with the development of CI. For instance, a nested case-control study with a long follow-up has reported that low serum FA levels are associated with an increased risk of disabling dementia [14]. Therefore, the above research findings prompted us to speculate whether periodontitis promotes CI by affecting folate levels.

In this study, data cross two cycles 2011–2012 and 2013–2014 of the National Health and Nutrition Examination Survey (NHANES), a nationally representative sample of the US population, we aimed to 1) explore the association between periodontitis and cognitive performance, as well as associations between periodontitis and exogenous or endogenous folate; 2) assess the potential mediating role of folate levels in the association between periodontitis and cognitive function.

2.1 Data source and study design

Data for this study was drawn from the 2011–2014 cycles of the NHANES (accessed on 1 October 2023) [15], which is a cross-sectional population-based health survey conducted by the U.S. National Center for Health Statistics (NCHS) of the Centers for Disease Control and Prevention. A complex, multistage, probability sampling design was used to select participants. Information was collected from questionnaires through face-to-face interviews and standardized medical examinations in a specially equipped mobile examination center (MEC). The NHANES cycles were ethically approved by the CDC's National Center for Health Statistics (NCHS) and Research Ethics Review Board (ERB). Before participation, all survey participants signed a written consent form. We followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines [16]. All survey participants aged 60 years or older with data for periodontal status, exogenous and endogenous folate levels, and cognitive function tests were included in this study. Cases with missing data on oral health examination, and cognitive function tests were excluded. Participants with a history of stroke were excluded, as the experience of stroke would affect individuals’ cognitive function.

2.2 Periodontitis assessment

Participants (≥ 60 y old) with at least one remaining tooth (excluding third molars) and not meeting any of the health exclusion criteria, were eligible for a full-mouth periodontal examination performed by licensed dentists. The diagnostic criteria for periodontitis in the NHANES were based on measurements of CAL and PD in specific teeth. Periodontitis cases were defined using the AAP/CDC criteria:≥2 interproximal sites with CAL ≥ 3 mm, and ≥ 2 interproximal sites with PD ≥ 4 mm (not on the same tooth) or one site with PD ≥ 5 mm [17]. Clinical attachment level (CAL) was measured at six specific sites on each tooth (mesiobuccal, midbuccal, distobuccal, mesiolingual/palatal, midlingual/palatal, and distolingual/palatal) using a periodontal probe (PCP2, HuFriedy). The CAL measurements were then averaged for each tooth. Probing depth (PD) refers to the depth of the gum pocket around a tooth, also measured in millimeters using a periodontal probe.

2.3 Cognitive function assessment

Participants aged ≥ 60 years were eligible for the cognitive functioning assessment in the NHANES. Cognitive function was evaluated using three cognitive tests: the CERAD word learning subtests (CERAD_WL), the animal fluency test (AFT), and the digit symbol substitution test (DSST). The CERAD_WL (raw score range: 0–40) is part of the Consortium to Establish a Registry for Alzheimer's Disease word learning subtests to evaluate vocabulary learning and memory abilities, including three consecutive immediate (CERAD_IR) and one delayed (CERAD_DR score) learning ability tests for new verbal information. The CERAD_WL score was obtained by adding CERAD_IR and CERAD_DR. In each immediate learning ability test, participants were asked to read about 10 unrelated words, then they were asked to recall as many words as possible. The AFT assesses categorical verbal fluency, which is a component of executive function. Participants were asked to name as many animals as possible within one minute. The DSST derived from the Wechsler Adult Intelligence Scale (WAIS-III), measures processing speed, sustained attention, and working memory [18]. Participants were required to copy symbols paired with numbers within a designated time. The scores obtained for each cognitive domain were then all scaled to 0–10 as previously reported [8, 19]. A general cognition score was calculated as the sum of the standardized z-scores of the CERAD_WL, AFT, and DSST tests.

2.4 Exogenous or endogenous folate

Dietary intake folate equivalents and dietary supplement folate were measured as exogenous folate. Serum and red blood cell (RBC) folate were measured as endogenous folate. Dietary intake folate equivalents and dietary supplement folate were collected during the two-day dietary interview, and the average level of the first and second-day intake was calculated. The serum total folate was measured by LC-MS/MS. Serum total folate (LBDFOTSI) was calculated by adding LBXSF1SI-LBXSF5SI. RBC folate concentration was measured with the microbiological assay method, and revised as in two steps. Firstly, whole blood folate (WBF) was calculated using original RBC folate, hematocrit (HCT), and original serum total folate. Then, revised RBC folate concentration was calculated from whole blood folate, the adjusted serum total folate, and HCT. Detailed calculation steps can be found in the NHANES laboratory protocols [20]. The periodontitis group was subdivided into four groups, groups with or without dietary supplement folate, and goups with high or low dietary intake folate equivalents according to the median level of dietary intake folate equivalent of periodontitis patients.

2.5 Covariates

Covariates based on background knowledge and prior literature (sociodemographic characteristics, health behaviors, disease history, and medical examination) were included. In detail, covariates included sociodemographic characteristics (age, gender, race, marital status, education level, annual family income, BMI) [21–24], health behaviors (alcohol intake, physical activity, smoking status (serum cotinine)) [25–27], disease history (hypertension, diabetes) [28, 29], and medical examination (Burine creatinine, hemoglobin, glycohemoglobin concentration) [30, 31].

2.6 Statistical analysis

Statistical software R (Version 4.3.0; R Core Team, 2023) was used for data analysis and description. Descriptive statistics such as absolute and relative frequencies for discrete parameters as well as the mean and standard deviation for continuous parameters were computed. Independent sample t-test and ${x}^{2}$ test was used to compare characteristics of covariates, cognitive scores, and folate levels between the periodontitis and non-periodontitis groups. To reduce the impact of the confounding effect on estimated associations, propensity score weighted logistic regression was used to estimate the associations between periodontitis and cognitive scores, and generalized propensity score weighted linear regression models were used to estimate the associations between dietary supplement folate serum total folate, and RBC folate and cognitive scores. The propensity score and generalized propensity score were calculated as conditional probability density functions of the exposure variables (periodontitis and folate levels) given pre-defined covariates. A covariate balanced state was defined as an average value of standardized mean difference and absolute correlation coefficients less than 0.1. Besides, within populations with periodontitis propensity scores weighted linear regression models were also used to estimate associations between dietary intake folate, dietary supplement folate, and cognitive scores. To reduce potential effects that might distort the estimated mediation effect, natural effect models built based on a counterfactual framework were then used to estimate the mediation effect of dietary supplemented folate, serum total folate, and RBC folate for the periodontitis-cognitive scores. Then proportions of mediation were calculated for mediators that have significant indirect effects. The significant level was set as α = 0.05. A P value less than and equal to 0.05 was considered statistically significant.

3.1 Study characteristics

A total of 1966 participants aged 60–80 years were included in the final analysis (the flow chart for screening participants was represented in Appendix Fig. 1), the average age was 68.70 ± 6.64 years, and among them, 974 (49.5%) were male, 992 (50.5%) were female. 869 (44.2%) participants were diagnosed with periodontitis. The average score of CERAD_IR, CERAD_DR, CERAD_WL, AFT, DSST, and General cognition score, and the average levels of dietary intake folate equivalents, dietary supplement folate, serum total folate, and RBC folate are listed in Table 1.

Table 1

Description of characteristics of included participants
Variables	$\varvec{N}\left(\varvec{\%}\right)/\stackrel{-}{\varvec{x}}\pm \varvec{s}$	Variables	$\varvec{N}\left(\varvec{\%}\right)/\stackrel{-}{\varvec{x}}\pm \varvec{s}$
Age (years)	68.70 ± 6.64	Diabetes
Gender		Yes	421 (21.4)
Male	974 (49.5)	No	1,545 (78.6)
Female	992 (50.5)	Glycohemoglobin (%)	6.05 ± 1.10
Ethnicity		HDL (mg/dL)	54.70 ± 16.04
Black	450 (22.9)	LDL (mg/dL)	112.41 ± 35.78
White	1,516 (77.1)	TC (mg/dL)	192.28 ± 43.04
Education		TG (mg/dL)	155.13 ± 105.91
College and above	1,088 (55.4)	Urine creatinine (mg/dL)	109.08 ± 69.62
High school and below	876 (44.6)	Hemoglobin (g/dL)	13.83 ± 1.40
Marital status		ALT (U/L)	22.65 ± 12.39
Married	1,182 (60.2)	AST (U/L)	25.29 ± 11.89
Not married	784 (39.8)	CPK (IU/L)	134.38 ± 100.92
Annual family income		Eosinophils percent (%)	3.08 ± 2.49
< $20000	411 (21.7)	Basophils percent (%)	0.75 ± 0.52
≥$20000	1555 (79.3)	ALB (g/dL)	4.21 ± 0.30
Alcohol consumption		CREA (mg/dL)	0.99 ± 0.54
At/below recommended	549 (28.2)	UA (mg/dL)	5.62 ± 1.40
Above recommended	484 (24.9)	25OHD2 (nmol/L)	6.23 ± 17.87
Less than 12 drinks/year	914 (46.9)	HEI	55.84 ± 12.10
Smoke		Lymphocyte percent (%)	29.42 ± 9.01
Ever	700 (35.7)	Periodontitis (%)	869 (44.2)
Never	1,047 (53.3)	Dietary intake folate Equivalents (mcg)	496.17 ± 274.25
Current	216 (11.0)	Dietary supplement Folate (mcg)	270.71 ± 881.68
BMI (Kg/m²)	28.96 ± 6.26	Serum total folate (nmol/L)	23.80 ± 14.00
Arm circumference (cm)	32.57 ± 4.74	RBC folate (nmol/L)	586.18 ± 263.68
Waist circumference (cm)	101.34 ± 14.54	CERAD_IR	19.15 ± 4.81
Sleep duration (hours)	7.12 ± 3.25	CERAD_DR	6.07 ± 2.36
Physical activity (METs)	33.50 ± 65.00	CERAD_WL	25.22 ± 6.74
SBP (mmHg)	132.31 ± 18.66	AFT	16.93 ± 5.49
DBP (mmHg)	68.30 ± 13.69	DSST	48.42 ± 16.93
Hypertension		General cognition score	80.06 ± 22.38
Yes	1,141 (58.2)
No	820 (41.8)
Note: BMI: body mass index (kg/m²); SBP: systolic blood pressure (mmHg); DBP: diastolic blood pressure (mmHg); HDL: high-density lipoprotein (mg/dL); LDL: low-density lipoprotein (mg/dL); TC: total cholesterol (mg/dL); TG: triglyceride (mg/dL); ALT: alanine aminotransferase (U/L); AST: aspartate aminotransferase (U/L); CPK: creatine phosphokinase (IU/L); ALB: albumin (g/dL); CREA: creatinine (mg/dL); UA: uric acid (mg/dL); 25OHD2: 25-hydroxyvitamin D2 (nmol/L); HEI: health eating index; RBC: red blood cell; CERAD_IR: CERAD Word Learning for immediate recall; CERAD_DR: CERAD Word Learning for delayed recall; CERAD_WL: CERAD Word Learning; AFT: animal fluency test; DSST: digit symbol substitution test.

Table 1

3.2 Comparision of characteristics between non-periodontitis and periodontitis

Comparisons of characteristics between the periodontitis and non-periodontitis groups in the elderly population demonstrated that the periodontitis group has younger age, higher proportion of males, higher proportion of black population, lower proportion of education level of college and above, higher proportion of participants drunk above recommended, higher proportion of current smoking participants, higher glycohemoglobin level, lower HDL level, higher hemoglobin, ALT, AST, and CPK level, and lower HEI (Table 2).

Table 2

Comparisons of characteristics between periodontitis and non-periodontitis
Variables	Non-Periodontitis (N = 1097)	Periodontitis (N = 869)	$\varvec{t}/{\varvec{x}}^{2}$	P value
Age (years)	69.25 ± 6.78	68.01 ± 6.39	4.159	< 0.001
Gender			57.491	< 0.001
Male	460 (41.9)	514 (59.1)
Female	637 (58.1)	355 (40.9)
Ethnicity			22.718	< 0.001
Black	207 (18.9)	243 (28.0)
White	890 (81.1)	626 (72.0)
Education			18.769	< 0.001
College and above	654 (59.7)	434 (49.9)
High school and below	441 (40.3)	435 (50.1)
Marital status			0.508	0.476
Married	652 (59.5)	530 (61.1)
Not married	445 (40.5)	339 (39.9)
Annual family income			0.465	0.495
< $20000	224 (21.2)	187 (22.5)
≥$20000	875 (78.8)	682 (78.5)
Alcohol consumption			6.804	0.033
At/below recommended	297 (27.3)	252 (29.4)
Above recommended	253 (23.2)	231 (26.9)
Less than 12 drinks/year	539 (49.5)	375 (43.7)
Smoke			46.549	< 0.001
Ever	386 (35.3)	314 (36.2)
Never	633 (57.8)	414 (47.7)
Current	76 (6.9)	140 (16.1)
BMI (Kg/m²)	29.02 ± 6.57	28.88 ± 5.86	0.508	0.612
Arm circumference (cm)	32.46 ± 4.93	32.71 ± 4.48	-1.155	0.248
Waist circumference (cm)	100.99 ± 14.80	101.78 ± 14.20	-1.187	0.235
Sleep duration (hours)	7.14 ± 3.10	7.09 ± 3.43	0.359	0.720
Physical activity (METs)	32.44 ± 60.64	34.85 ± 70.13	-0.817	0.414
SBP (mmHg)	132.01 ± 18.74	132.68 ± 18.57	-0.746	0.456
DBP (mmHg)	67.87 ± 13.42	68.85 ± 14.00	-1.502	0.133
Hypertension			1.637	0.201
Yes	651 (59.5)	490 (56.6)
No	444 (40.5)	376 (43.4)
Diabetes			0.295	0.587
Yes	230 (21.0)	191 (22.0)
No	867 (79.0)	678 (78.0)
Glycohemoglobin (%)	6.01 ± 0.97	6.11 ± 1.24	-1.971	0.049
HDL (mg/dL)	55.67 ± 16.30	53.48 ± 15.62	2.958	0.003
LDL (mg/dL)	112.17 ± 35.97	112.72 ± 35.58	-0.227	0.820
TC (mg/dL)	192.60 ± 43.72	191.89 ± 42.18	0.356	0.722
TG (mg/dL)	151.62 ± 99.41	159.58 ± 113.50	-1.616	0.106
Urine creatinine (mg/dL)	106.82 ± 69.23	111.96 ± 70.05	-1.617	0.106
Hemoglobin (g/dL)	13.70 ± 1.37	13.99 ± 1.42	-4.603	< 0.001
ALT (U/L)	22.01 ± 10.41	23.46 ± 14.47	-2.433	0.015
AST (U/L)	24.79 ± 9.56	25.94 ± 14.29	-1.993	0.046
CPK (IU/L)	127.27 ± 96.32	143.37 ± 105.83	-3.402	0.001
Eosinophils percent (%)	3.06 ± 2.44	3.11 ± 2.55	-0.443	0.657
Basophils percent (%)	0.74 ± 0.47	0.77 ± 0.57	-1.417	0.157
ALB (g/dL)	4.19 ± 0.29	4.22 ± 0.31	-1.701	0.088
CREA (mg/dL)	0.99 ± 0.57	1.00 ± 0.51	-0.215	0.829
UA (mg/dL)	5.60 ± 1.42	5.65 ± 1.38	-0.743	0.457
25OHD2 (nmol/L)	6.43 ± 17.78	5.97 ± 17.98	0.558	0.577
HEI	56.84 ± 12.22	54.52 ± 11.81	3.958	< 0.001
Lymphocyte percent (%)	29.33 ± 8.80	29.54 ± 9.27	-0.502	0.615
Note: BMI: body mass index (kg/m²); SBP: systolic blood pressure (mmHg); DBP: diastolic blood pressure (mmHg); HDL: direct HDL-cholesterol (mg/dL); LDL: direct LDL-cholesterol (mg/dL); TC: total cholesterol (mg/dL); TG: triglyceride (mg/dL); ALT: alanine aminotransferase (U/L); AST: aspartate aminotransferase (U/L); CPK: creatine phosphokinase (IU/L); ALB: albumin (g/dL); CREA: creatinine (mg/dL); UA: uric acid (mg/dL); 25OHD2: 25-hydroxyvitamin D2 (nmol/L); HEI: health eating index; CERAD_IR: CERAD Word Learning for immediate recall; CERAD_DR: CERAD Word Learning for delayed recall; CERAD_WL: CERAD Word Learning; AFT: animal fluency test; DSST: digit symbol substitution test. P values in bold font are less than 0.05.

Table 2

3.3 Comparision of folate and cognitive function between non-periodontitis and periodontitis

Comparison between the periodontitis and non-periodontitis groups demonstrated that the periodontitis group had significantly lower average levels of dietary supplement folate, serum total folate, and RBC folate, while the difference in dietary intake folate equivalents between non-periodontitis and periodontitis was non-significant (Appendix Fig. 2). Besides, the periodontitis group also has significantly lower cognitive scores, including CERAD_IR, CERAD_WL, DSST, and general cognition scores (Table 3).

Table 3

Comparisons of folate and cognitive function between periodontitis and non-periodontitis
Variables	Non-Periodontitis (N = 1097)	Periodontitis (N = 869)	$\varvec{t}/{\varvec{x}}^{2}$	P value
Dietary intake folate equivalents (mcg)	498.58 ± 294.49	492.98 ± 244.97	0.418	0.675
Dietary supplement folate (mcg)	315.51 ± 1,124.32	214.14 ± 397.40	2.775	0.006
Serum total folate (nmol/L)	25.28 ± 15.12	21.90 ± 12.18	5.343	< 0.001
RBC folate (nmol/L)	612.53 ± 269.69	552.90 ± 252.15	4.947	< 0.001
CERAD_IR	19.47 ± 4.82	18.75 ± 4.76	3.310	0.001
CERAD_DR	6.16 ± 2.38	5.96 ± 2.32	1.866	0.062
CERAD_WL	25.63 ± 6.75	24.71 ± 6.69	3.024	0.003
AFT	17.10 ± 5.51	16.71 ± 5.45	1.534	0.125
DSST	50.06 ± 16.77	46.34 ± 16.91	4.782	< 0.001
General cognition score	82.16 ± 22.39	77.40 ± 22.09	4.626	< 0.001
Note: RBC: red blood cell; CERAD_IR: CERAD Word Learning for immediate recall; CERAD_DR: CERAD Word Learning for delayed recall; CERAD_WL: CERAD Word Learning; AFT: animal fluency test; DSST: digit symbol substitution test. P values in bold font are less than 0.05.

Table 3

3.4 Associations between periodontitis, dietary supplement folate, serum total folate, RBC folate, and cognitive function

The absolute standardized mean difference and absolute correlation coefficients for covariates are listed in Appendix Table 1. The average level of absolute standardized mean difference was 0.003 (below 0.1) for the association between periodontitis and cognitive scores, which indicated a balanced state of the included covariates (Fig. 1A). Besides, the average level of absolute correlation coefficients was 0.014 (below 0.1) for dietary supplement folate (Fig. 1B), 0.025 (below 0.1) for serum total folate (Fig. 1C), and 0.058 (below 0.1) for RBC folate (Fig. 1D).

Furthermore, periodontitis was significantly related to the general cognition score (t = -3.307, P = 0.001) and CERAD_IR (t = -2.493, P = 0.013), CERAD_WL (t = -2.287, P = 0.022), DSST (t = -4.312, P < 0.001). In the generalized propensity score weighting linear regression, dietary supplement folate was significantly related to the general cognition score (t = 2.933, P = 0.003) and DSST (t = 3.815, P < 0.001). Serum total folate was significantly related to the general cognition score (t = 3.418, P = 0.001) and CERAD_IR (t = 2.637, P = 0.008), CERAD_DR (t = 2.194, P = 0.028), CERAD_WL (t = 2.655, P = 0.008), AFT (t = 2.794, P = 0.005), DSST (t = 2.699, P = 0.007). And RBC folate was significantly related to the general cognition score (t = 2.995, P = 0.003) and DSST (t = 4.193, P < 0.001) (Table 4).

Table 4

Generalized/propensity score weighting linear regression for association between periodontitis, dietary supplement folate, serum total folate, RBC folate level, and cognitive scores
Exposure	Cognitive test	B	SE	t	P value
Periodontitis	General cognition score	-0.380	0.115	-3.307	0.001
	CERAD_IR	-0.555	0.223	-2.493	0.013
	CERAD_DR	-0.163	0.112	-1.452	0.147
	CERAD_WL	-0.718	0.314	-2.287	0.022
	AFT	-0.345	0.271	-1.272	0.204
	DSST	-3.574	0.829	-4.312	< 0.001
Dietary supplement folate	General cognition score	< 0.001	< 0.001	2.933	0.003
	CERAD_IR	< 0.001	< 0.001	1.095	0.274
	CERAD_DR	< 0.001	< 0.001	1.704	0.089
	CERAD_WL	0.001	< 0.001	1.384	0.166
	AFT	0.001	< 0.001	1.761	0.078
	DSST	0.004	0.001	3.815	< 0.001
Serum total folate	General cognition score	0.016	0.005	3.418	0.001
	CERAD_IR	0.024	0.009	2.637	0.008
	CERAD_DR	0.010	0.005	2.194	0.028
	CERAD_WL	0.033	0.013	2.655	0.008
	AFT	0.030	0.011	2.794	0.005
	DSST	0.090	0.033	2.699	0.007
RBC folate	General cognition score	0.001	< 0.001	2.995	0.003
	CERAD_IR	< 0.001	< 0.001	0.578	0.563
	CERAD_DR	< 0.001	< 0.001	1.812	0.070
	CERAD_WL	0.001	0.001	1.053	0.292
	AFT	0.001	0.001	1.861	0.063
	DSST	0.007	0.002	4.193	< 0.001
Note: CERAD_IR: CERAD Word Learning for immediate recall; CERAD_DR: CERAD Word Learning for delayed recall; CERAD_WL: CERAD Word Learning; AFT: Animal Fluency test; DSST: Digit Symbol Substitution test; RBC: red blood cell. P values in bold font are less than 0.05.

Table 4

3.5 The mediation effect of folate for periodontitis and cognitive function

The mediation effect of dietary supplement folate was significant for periodontitis-general cognition score (B = -0.019, P = 0.034) and periodontitis-DSST (B = -0.187, P = 0.013). The proportion of mediation was 0.084 (-0.019/-0.225) and 0.094 (-0.187/-1.975) for the general cognition score and DSST, respectively. The mediation effect of serum total folate was significant for periodontitis-general cognition score (B = -0.021, P = 0.036), periodontitis-AFT (B = -0.055, P = 0.039), and periodontitis-DSST (B = -0.132, P = 0.041). The proportion of mediation was 0.091 (-0.021/-0.229), 0.171(-0.055/-0.320), and 0.066 (-0.132/-1.991) for the general cognition score, AFT, and DSST, respectively. Besides, RBC folate was significant for periodontitis-general cognition score (B = -0.021, P = 0.032), periodontitis-AFT (B = -0.046, P = 0.045), and periodontitis-DSST (B = -0.180, P = 0.020). The proportion of mediation was 0.091 (-0.021/-0.229), 0.138(-0.046/-0.334), and 0.091 (-0.180/-1.986) for the general cognition score, AFT, and DSST, respectively (Appendix Table 2).

3.6 Periodontitis cases with higher exogenous folate have better cognitive function

To further detect the effect of exogenous folate on the cognitive function of patients with periodontitis, a comparison of cognitive scores between periodontitis patients with (264) and without (605) dietary supplement folate was performed. Results demonstrated that the periodontitis group with dietary supplement folate had higher CERAD_IR, DSST, and general cognition scores, higher serum total, and RBC folate levels than that of the periodontitis group without dietary supplement folate (Appendix Table 3). Furthermore, after the weighting step (Appendix Table 4 and Appendix Fig. 3A), in the propensity score weighted linear regression models, the population with dietary supplement folate has a higher general cognition score (B = -0.571, P = 0.002, Appendix Table 5).

Comparison of cognitive scores between periodontitis patients with high (n = 318) and low (n = 420) dietary intake folate equivalents showed that the periodontitis group with high dietary intake folate equivalents had higher AFT, DSST, and general cognition scores, higher serum total and RBC folate levels (Appendix Table 6). After the weighting step (Appendix Table 7 and Appendix Fig. 3B), in the propensity score weighted linear regression models, the population with high dietary intake folate has a higher general cognition score (B = 0.400, P = 0.024, Appendix Table 8).

This population-based cross-sectional study found that periodontitis, dietary supplement folate, serum total folate, and RBC folate were significantly related to cognitive scores. Especially, from the perspective of treating folate as a mediator for the periodontitis-cognitive function, this study further revealed that the mediation effect of the three forms of folate was significant for periodontitis-cognitive scores. Notably, periodontitis cases with higher exogenous folate have higher cognitive scores. These results demonstrated that exogenous and endogenous folate played important roles in periodontitis-related CI.

To date, understanding dementia and its risk factors has been greatly accomplished through large population-based surveys [9, 32, 33]. Besides aging, periodontitis has been reported to be associated with the development of CI. For instance, Marruganti and colleagues have shown that periodontitis was significantly associated with low cognitive performance by using the data from 2086 older adults (≥ 60 years old) from the NHANES 2011–2014 database [8]. Chen and colleagues reported that patients with 10 years of periodontitis exposure exhibited a 1.7-fold higher risk of developing AD than unexposed groups in a retrospective, population-based, and matched-cohort study [34]. Moreover, a longitudinal analysis of a large cohort of U.S. adults aged between 45–64 years who were enrolled in the Atherosclerosis Risk in Communities study reported a significant association between severe periodontitis and incident dementia [33]. Consistent with the previous studies, the present study also supported that periodontitis was significantly associated with low cognitive function, especially, with vocabulary learning and memory abilities (CERAD_WL), processing speed, sustained attention, and working memory (DSST).

Although it is well known that periodontitis is a vital risk factor for CI, the biological mechanisms for the association between periodontitis and CI have not been fully elucidated yet. Recently, the nested case-control study with a long follow-up demonstrated that low serum total folate level was associated with an increased risk of disabling dementia among Japanese individuals [14]. However, little was known about whether folate was the mediator between periodontitis and cognitive impairment. The results of this study indicated that the periodontitis group had lower serum total and RBC folate, while there was no significant difference in the dietary intake folate. A possible reason may be that periodontitis can cause chewing disability, leading to a lack of nutrition intake, resulting in a low serum total and RBC folate level [35]. Another possible reason was that the system inflammation and dental microbiome induced by periodontitis caused the decrease of endogenous folate [36–38]. Moreover, lower dietary supplement folate, serum total, and RBC folate levels were significantly associated with lower cognitive scores. There were significant mediation effects of serum total and RBC folate levels between periodontitis and general cognition score, suggesting serum total and RBC folate levels were mediators in the association between periodontitis and CI. Notably, the periodontitis group with dietary supplement folate or high dietary intake folate has better cognitive function than that of periodontitis cases without dietary supplement or with low dietary intake folate. These results demonstrate that endogenous folate is an important mediator between periodontitis and CI among the elderly population, and exogenous supplement folate can prevent patients with periodontitis from suffering from CI.

Several previous studies have reported the underlying mechanism of folate deficiency promoting CI. Folate can regulate homocysteine metabolism and high serum homocysteine levels are associated with dementia [39]. Moreover, folate deficiency has been proven to be directly related to amyloid toxicity through its impairment of neuronal DNA repair and consequent sensitization of neurons to oxidative damage-induced amyloid-β in animal AD models [40]. Besides, folate supplements can ameliorate the memory and learning deficits induced by LPS by normalizing the inflammatory response and oxidative stress markers in the brain [11]. However, periodontitis may directly promote CI. Periodontitis-related systemic inflammation may contribute to neurodegeneration by activating microglia and releasing proinflammatory molecules [37]. In addition, oral bacterial genomic signatures, such as the keystone pathogen Porphyromonas gingivalis (PG), have been observed in AD brain tissues, and inhibition of the toxic proteases gingipain from the PG blocked Aβ_1–42 production, reduced neuroinflammation, and rescued neurons in the hippocampus [38].

Our study also has several limitations. First, the data was obtained from NHANES which is a cross-sectional survey, and the conclusion might be distorted due to confounding effects. Although propensity score weighting regression models were used to estimate exposure-outcome and mediation-outcome associations, unobserved confounders might still damage these estimated associations. Secondly, as the mediation effect of folate on the association between periodontitis and cognition was estimated, it is required in mediation models that the exposure be collected before the mediator, and the mediator be observed before the outcome. However, due to the cross-sectional design, this time sequence assumption might have been violated. Finally, further in vivo and in vitro preliminary experiments and clinical experiments are required to investigate the biological mechanism of periodontitis-promoted CI through mediating folate.

Our study demonstrates that periodontitis is associated with CI by affecting serum total and RBC folate among elderly adults. In addition, higher dietary supplement folate and dietary intake folate with an improvement in serum total and RBC folate levels can decrease the risk for patients with periodontitis suffering from CI.

Author contributions

Fei Liu: Contributed to the conception, design, data acquisition and interpretation, drafted and critically revised the manuscript; Jian-Song Mei: Contributed to data acquisition and interpretation, and critically revised the manuscript; Jia-Shuo Zhao: Contributed to data interpretation, and critically revised the manuscript; Yu-Heng Feng: Contributed to data analysis, and critically revised the manuscript; Yan-Yan Zhang: Contributed to data acquisition and interpretation, critically revised the manuscript; Qing Pan: Contributed to the conception, design, data analysis, and interpretation, drafted the manuscript and critically revised manuscript; Jie-Fei Shen: Contributed to the conception, design, data interpretation, and critically revised the manuscript; All authors gave their final approval and agree to be accountable for all aspects of the work.

Acknowledgments

We would like to express our sincere gratitude to the NHANES staff, investigators, and the participants involved in the NHANES study.

Funding information

This work was funded by the National Natural Science Foundation of China (Grant No. 82071149), the Science and Technology Department of Sichuan Province (Grant No. 2021JDRC0166), and the China Postdoctoral Science Foundation (Grant Number: 2020M683329).

Conflict of Interest

The authors declare no conflicts of interest.

Data availability statement

The data that support the findings of this study are openly available at: https://www.cdc.gov/nchs/nhanes/index.htm.

Ethics statement

The research ethics review boards of National Center for Health Statistics authorized the NHANES study protocols and all participants provided written informed consent.

Association As. Alzheimer’s facts and figures. Alzheimer's Dement J Alzheimer's Assoc. 2023;19.
Wu YT, Beiser AS, Breteler MMB, Fratiglioni L, Helmer C, Hendrie HC, et al. The changing prevalence and incidence of dementia over time - current evidence. Nat reviews Neurol. 2017;13:327–39.
Nichols E, Steinmetz JD, Vollset SE, Fukutaki K, Chalek J, Abd-Allah F, et al. Estimation of the global prevalence of dementia in 2019 and forecasted prevalence in 2050: an analysis for the Global Burden of Disease Study 2019. Lancet Public health. 2022;7:e105–e25.
Eke PI, Thornton-Evans GO, Wei L, Borgnakke WS, Dye BA, Genco RJ. Periodontitis in US Adults: National Health and Nutrition Examination Survey 2009–2014. Journal of the American Dental Association (1939). 2018;149:576 – 88.e6.
Zhao C, Kuraji R, Ye C, Gao L, Radaic A, Kamarajan P, et al. Nisin a probiotic bacteriocin mitigates brain microbiome dysbiosis and Alzheimer's disease-like neuroinflammation triggered by periodontal disease. J Neuroinflamm. 2023;20:228.
Singhrao SK, Harding A, Poole S, Kesavalu L, Crean S. Porphyromonas gingivalis Periodontal Infection and Its Putative Links with Alzheimer's Disease. Mediators Inflamm. 2015;2015:137357.
Elwishahy A, Antia K, Bhusari S, Ilechukwu NC, Horstick O, Winkler V. Porphyromonas Gingivalis as a Risk Factor to Alzheimer's Disease: A Systematic Review. J Alzheimer's disease Rep. 2021;5:721–32.
Marruganti C, Baima G, Aimetti M, Grandini S, Sanz M, Romandini M. Periodontitis and low cognitive performance: A population-based study. J Clin Periodontol. 2023;50:418–29.
Yoo JE, Huh Y, Park SH, Han K, Park HS, Cho KH, et al. Association between Dental Diseases and Oral Hygiene Care and the Risk of Dementia: A Retrospective Cohort Study. Journal of the American Medical Directors Association; 2023.
Yamaguchi S, Murakami T, Satoh M, Komiyama T, Ohi T, Miyoshi Y, et al. Associations of Dental Health With the Progression of Hippocampal Atrophy in Community-Dwelling Individuals: The Ohasama Study. Neurology. 2023;101:e1056–e68.
Darbandi ZK, Amirahmadi S, Goudarzi I, Hosseini M, Rajabian A. Folic acid improved memory and learning function in a rat model of neuroinflammation induced by lipopolysaccharide. Inflammopharmacology. 2023.
Kakhki S, Goodarzi M, Abbaszade-Cheragheali A, Rajabi M, Masoumipour AH, Khatibi SR et al. Folic acid supplementation improved cognitive deficits associated with lithium administration during pregnancy in rat offspring. Int J Dev neuroscience: official J Int Soc Dev Neurosci. 2023.
Fan J, Ma Z, Zheng Y, Zhang M, Huang L, Liu H. Folate Deficiency Increased Microglial Amyloid-β Phagocytosis via the RAGE Receptor in Chronic Unpredictable Mild-Stress Rat and BV2 Cells. Nutrients. 2023;15.
Kishida R, Yamagishi K, Ikeda A, Hayama-Terada M, Shimizu Y, Muraki I et al. Serum folate and risk of disabling dementia: a community-based nested case-control study. Nutr Neurosci. 2023:1–7.
NHANES. The National Health and Nutrition Examination Survey. [cited 2021 Oct 13. 2021;https://www.cdc.gov/nchs/nhanes/index.htm.
von Elm E, Altman DG, Egger M, Pocock SJ, Gøtzsche PC, Vandenbroucke JP. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies. J Clin Epidemiol. 2008;61:344–9.
Eke PI, Page RC, Wei L, Thornton-Evans G, Genco RJ. Update of the case definitions for population-based surveillance of periodontitis. J Periodontol. 2012;83:1449–54.
Ryan JJ, Lopez SJ. Wechsler Adult Intelligence Scale-III. In W. I. Dorfman & M. Hersen, editors, Understanding psychological assessment (pp. 19–42). Springer US. 2001; https://doi.org/10.1007/978-1-4615-1185-4_2.
Zhang Q, Zhang M, Chen Y, Cao Y, Dong G. Nonlinear Relationship of Non-High-Density Lipoprotein Cholesterol and Cognitive Function in American Elders: A Cross-Sectional NHANES Study (2011–2014). J Alzheimer's disease: JAD. 2022;86:125–34.
NHANES. National Health and Nutrition Examination Survey 2011–2012 Data Documentation, Codebook, and Frequencies. 2014.
Kornblith E, Bahorik A, Boscardin WJ, Xia F, Barnes DE, Yaffe K. Association of Race and Ethnicity With Incidence of Dementia Among Older Adults. JAMA. 2022;327:1488–95.
Eke PI, Borgnakke WS, Genco RJ. Recent epidemiologic trends in periodontitis in the USA. Periodontology. 2000. 2020;82:257 – 67.
Hebert LE, Weuve J, Scherr PA, Evans DA. Alzheimer disease in the United States (2010–2050) estimated using the 2010 census. Neurology. 2013;80:1778–83.
Chen ZC, Wu H, Wang XD, Zeng Y, Huang G, Lv Y et al. Association between marital status and cognitive impairment based on a cross-sectional study in China. Int J Geriatr Psychiatry. 2022;37.
Anstey KJ, von Sanden C, Salim A, O'Kearney R. Smoking as a risk factor for dementia and cognitive decline: a meta-analysis of prospective studies. Am J Epidemiol. 2007;166:367–78.
Jia RX, Liang JH, Xu Y, Wang YQ. Effects of physical activity and exercise on the cognitive function of patients with Alzheimer disease: a meta-analysis. BMC Geriatr. 2019;19:181.
Visontay R, Rao RT, Mewton L. Alcohol use and dementia: new research directions. Curr Opin Psychiatry. 2021;34:165–70.
Palta P, Carlson MC, Crum RM, Colantuoni E, Sharrett AR, Yasar S et al. Diabetes and Cognitive Decline in Older Adults: The Ginkgo Evaluation of Memory Study. The journals of gerontology Series A, Biological sciences and medical sciences. 2017;73:123–30.
Walker KA, Power MC, Gottesman RF. Defining the Relationship Between Hypertension, Cognitive Decline, and Dementia: a Review. Curr Hypertens Rep. 2017;19:24.
Oh YS, Kim JS, Park HE, Song IU, Park JW, Yang DW, et al. Association between urine protein/creatinine ratio and cognitive dysfunction in Lewy body disorders. J Neurol Sci. 2016;362:258–62.
Schneider AL, Jonassaint C, Sharrett AR, Mosley TH, Astor BC, Selvin E et al. Hemoglobin, Anemia, and Cognitive Function: The Atherosclerosis Risk in Communities Study. The journals of gerontology Series A, Biological sciences and medical sciences. 2016;71:772–9.
Marruganti C, Baima G, Aimetti M, Grandini S, Sanz M, Romandini M. Periodontitis and low cognitive performance: A population-based study. J Clin Periodontol. 2023;50:418–29.
Demmer RT, Norby FL, Lakshminarayan K, Walker KA, Pankow JS, Folsom AR, et al. Periodontal disease and incident dementia: The Atherosclerosis Risk in Communities Study (ARIC). Neurology. 2020;95:e1660–e71.
Chen CK, Wu YT, Chang YC. Association between chronic periodontitis and the risk of Alzheimer's disease: a retrospective, population-based, matched-cohort study. Alzheimers Res Ther. 2017;9:56.
Kossioni AE. The Association of Poor Oral Health Parameters with Malnutrition in Older Adults: A Review Considering the Potential Implications for Cognitive Impairment. Nutrients. 2018;10.
Na HS, Jung NY, Song Y, Kim SY, Kim HJ, Lee JY et al. A distinctive subgingival microbiome in patients with periodontitis and Alzheimer's disease compared with cognitively unimpaired periodontitis patients. J Clin Periodontol. 2023.
Liccardo D, Marzano F, Carraturo F, Guida M, Femminella GD, Bencivenga L et al. Potential Bidirectional Relationship Between Periodontitis and Alzheimer's Disease. Front Physiol. 2020;11.
Dominy SS, Lynch C, Ermini F, Benedyk M, Marczyk A, Konradi A, et al. Porphyromonas gingivalis in Alzheimer's disease brains: Evidence for disease causation and treatment with small-molecule inhibitors. Sci Adv. 2019;5:eaau3333.
Smith AD, Refsum H, Bottiglieri T, Fenech M, Hooshmand B, McCaddon A, et al. Homocysteine and Dementia: An International Consensus Statement. J Alzheimers Dis. 2018;62:561–70.
Kruman II, Kumaravel TS, Lohani A, Pedersen WA, Cutler RG, Kruman Y, et al. Folic acid deficiency and homocysteine impair DNA repair in hippocampal neurons and sensitize them to amyloid toxicity in experimental models of Alzheimer's disease. J Neurosci. 2002;22:1752–62.

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Folate mediates cognitive impairment of aged people with periodontitis

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Abstract

Aims

Materials and Methods

Results

Conclusions

Figures

Clinical Relevance

1. Introduction

2. Materials and Methods

2.1 Data source and study design

2.2 Periodontitis assessment

2.3 Cognitive function assessment

2.4 Exogenous or endogenous folate

2.5 Covariates

2.6 Statistical analysis

3 Results

3.1 Study characteristics

3.2 Comparision of characteristics between non-periodontitis and periodontitis

3.3 Comparision of folate and cognitive function between non-periodontitis and periodontitis

3.4 Associations between periodontitis, dietary supplement folate, serum total folate, RBC folate, and cognitive function

3.5 The mediation effect of folate for periodontitis and cognitive function

3.6 Periodontitis cases with higher exogenous folate have better cognitive function

4 Discussion

5. Conclusion

Declarations

References

Additional Declarations

Supplementary Files

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