Association Between Dietary Theobromine and Cognitive Function in a Representative Elderly American Population: A Cross-Sectional Study

Abstract

Background: Despite reports on neuroprotective effects of dietary theobromine intake, whether dietary theobromine can exert beneficial effects on cognitive function is unclear. We aimed to investigate the association between dietary theobromine and cognitive function in old American population.

Methods: We collected data from the 2011-2012 and 2013-2014 cycles of the National Health and Nutrition Examination Survey, a cross-sectional survey. Daily dietary theobromine was treated as a continuous variable and a log transform. Cognitive function was measured by four tests: Consortium to Establish a Registry for Alzheimer's Disease (CERAD) Word Learning tests, CERAD delayed recall test, animal fluency test, and digit symbol substitution test (DSST). We conducted linear regression analyses and subgroup analyses to study the association between theobromine intake and cognitive performance. Basic characteristics, lifestyle factors, disease history, and nutritional intake were adjusted in these models.

Results: A total of 2,845 participants were included in this study. Daily theobromine intake was not significantly different between the 2011-2012 and 2013-2014 cycles. The CERAD-immediate and delayed recall scores were significantly different between these two cycles, but not the animal fluency score or digital symbol score. The daily dietary theobromine intake in log form was positively associated with immediate recall score (β, 95% CI, P: 0.661, 0.222-1.101, <0.01), delayed recall score (β, 95% CI, P: 0.232, 0.016-0.449, 0.04), and DSST score (β, 95% CI, P: 1.395, 0.140-2.649, 0.03) in the fully adjusted model, but not with the animal fluency score (β, 95% CI: 0.001, -0.122-0.907, 0.13). Sensitive analyses showed that L-theobromine intake was linearly associated with cognitive performance.

Conclusions: Daily theobromine intake was associated with cognitive performance in a large national representative population. However, further research is needed in order to corroborate our findings.

Background

Age-related cognitive decline, characterized by impairment of episodic memory, working memory, and attention, can affect the quality of life (1). Nutritional conditions are reported to be involved in this degenerative cognitive impairment (2, 3). Since previous studies have reported a protective effect of chocolate (4, 5), and theobromine is one of its main active components (6), it could also be associated with cognitive function.

In animal experiments, dietary theobromine is suggested to exert cognitive protection. Theobromine intake is reported to be capable of crossing the blood-brain barrier in mice(7), which provide theobromine chance to interact directly with brain tissue. Further, theobromine is estimated to exert protective effects through neurotransmitter regulation. For example, Mendiola-Precoma et al. (8) found that theobromine intake could improve A1 receptor expression. Theobromine might play a role in phosphodiesterase inhibitors to enhance motor learning skills (9).

Despite this evidence, few clinical trials have investigated the association between dietary theobromine and cognitive function. Therefore, we included a large, representative sample of ≥ 60-year-old American participants from the cross-sectional National Health and Nutrition Examination Survey (NHANES) dataset to study the association between daily theobromine intake and cognitive performance. We hypothesized that daily theobromine intake would be positively associated with cognitive performance.

Methods

Results

The recruited participants completed a cognitive questionnaire together with the first questionnaire from the 2011–2012 and 2013–2014 NHANES surveys. As shown in Fig. 1, this study included 2,854 elderly American participants.

The mean age of study participants was 69.4 years. Study participants had a mean score of 19.0 for the CERAD word list learning test, 5.9 for the CERAD recall test, 16.7 for the animal fluency test, and 46.2 for the digital symbol test. The mean CERAD word list learning test score was 1.7 points higher in the 2013–2014 cycle than in the 2011–2012 cycle, while the mean CERAD recall test was 0.7 points higher. The animal fluency test and digital symbol test were not significantly different in the 2011–2014 two cycles. Mean theobromine intake was 81.8 mg/d. Theobromine intake did not significantly vary between the 2011–2012 and 2013–2014 cycles. The characteristics of other covariates are presented in Table 1.

Table 2 Weighted regression models evaluating association between dietary theobromine intake and cognitive performance.

 ¹Adjusted non-variables: Age, sex, race, education, marital status, home status, employment, smoking status, BMI, history of disease, heart disease, history of stroke, hypertension, diabetes, depression, sleep disorder, and sex were adjusted.

²Adjusted model I for sex, age, race, education, marriage, home status, and employment.

³Adjusted for sex, age, race, education, marriage, home status, employment, smoking status, BMI, history of disease, heart disease, history of stroke, hypertension, diabetes, depression, and sleep disorder.

⁴Adjusted model III for sex, age, race, education, marriage, home status, employment, smoking status, BMI, history of disease, heart disease, history of stroke, hypertension, diabetes, depression, sleep disorder, and dietary nutrients (including alcohol, energy, protein, lutein, zeaxanthin, folic acid, vitamin B12, vitamin B12, vitamin D, magnesium, iron, zinc, copper, selenium, and caffeine).

Abbreviations: Consortium to Establish a Registry for Alzheimer's disease, CERAD.

Figure 2 presents a weighted distribution of daily theobromine intake in log form with respect to quartiles of immediate recall score, delayed recall score, animal fluency score, and DSST score. Daily theobromine intake was not significantly different among these quartile subgroups. As shown in Supplementary Fig. 1, daily theobromine intake did not follow a normal distribution. However, the log transformation distribution did. Thus, we used a continuous form and a log transform of daily theobromine intake to analyze the association between dietary theobromine and cognitive performance, as shown in Table 3 In the initial model, log transformation of daily theobromine intake was significantly associated with immediate recall test score (β, 95%CI, P value: 0.588, 0.151–1.025, 0.01), animal fluency test score (β, 95%CI, P value: 0.729, 0.194–1.264, < 0.01), and DSST score (β, 95%CI, P value: 1.525, -0.002-3.053, 0.05), but not with the delayed recall test (β, 95%CI, P value: 0.172, -0.041-0.386, 0.11). In the fully adjusted model, dietary theobromine intake was positively associated with immediate recall score (β, 95% CI, P: 0.661, 0.222–1.101, < 0.01), delayed recall score (β, 95% CI, P = 0.232, 0.016–0.449, 0.04), and DSST score (β, 95%CI, P value: 0.009, 0.004–0.015, < 0.01). Daily theobromine intake was not associated with the poor cognitive function measured by the four indexes, independent of whether confounding variables were adjusted or not.

To study the association between theobromine intake and cognitive performance we performed subgroup analyses. Theobromine was significantly positively associated with immediate recall score in those who never-smoked (β, 95%CI, P value: 0.006, 0.003–0.010, < 0.01), had hypertension (β, 95%CI, P value: 0.004, 0.001–0.008, 0.02), but not depression (β, 95%CI, P value: 0.005, 0.002–0.008, < 0.01), the 3rd quartile of daily energy (β, 95%CI, P value: 0.002, 0.002–0.011, < 0.01), and protein (β, 95%CI, P value: 0.006, 0.001–0.010, 0.01) intake.

Daily theobromine intake was negatively associated with delayed recall test scores in males (β, 95%CI, P value: -0.002, -0.004-0.000, 0.02), age > 80 (β, 95%CI, P value: -0.004, -0.008-0.000, 0.03), and the 3rd quartile of Lutein + Zeaxanthin (β, 95%CI, P value: -0.004, -0.006- -0.001, < 0.01). However, it was positively associated with delayed recall test scores in the 2nd quartile of Lutein + Zeaxanthin (β, 95%CI, P value: 0.004, 0.001–0.007, 0.01).

Theobromine intake was positively associated with animal fluency score in never-smokers (β, 95%CI, P value: 0.006, 0.002–0.011, < 0.01), normal BMI (β, 95%CI, P value: 0.010, 0.004 − 0.0015, < 0.01), non-depression (β, 95%CI, P value: 0.004, 0.000-0.007, 0.04), the 2nd quartile of Lutein + Zeaxanthin (β, 95%CI, P value: 0.008, 0.002–0.015, 0.01), and the highest quartile of vitamin D2 + D3 (β, 95%CI, P value: 0.008, 0.002–0.015, 0.01) subgroups.

In terms of execution ability, theobromine was associated with DSST score among age > 60 and ≤ 70 years old (β, 95%CI, P value: 0.011, 0.005–0.017, < 0.01), non-Hispanic white race (β, 95%CI, P value: 0.011, 0.004–0.018, 0.01), collage graduate or above (β, 95%CI, P value: 0.011, 0.003–0.019, 0.01), never-smoker (β, 95%CI, P value: 0.020, 0.010–0.031, < 0.01), overweight (β, 95%CI, P value: 0.010, 0.004–0.016, < 0.01), no history of stroke (β, 95%CI, P value: 0.010, 0.004–0.015, < 0.01), hypertension (β, 95%CI, P value: 0.012, 0.005–0.018, < 0.01), non-diabetes (β, 95%CI, P value: 0.012, 0.005–0.018, < 0.01), and depression (β, 95%CI, P value: 0.016, 0.008–0.024, < 0.01) subgroups. With respect to nutrition subgroups, theobromine was also positively associated with DSST among the 3rd (β, 95%CI, P value: 0.016, 0.002–0.031, 0.02) and 4th (β, 95%CI, P value: 0.009, 0.003–0.015, 0.01) quartile of energy intake. In the highest quartile of protein (β, 95%CI, P value: 0.017, 0.005–0.029, 0.01), lutein + zeaxanthin (β, 95%CI, P value: 0.027, 0.015–0.038, < 0.01), vitamin B12 (β, 95%CI, P value: 0.030, 0.017–0.043, < 0.01), and vitamin D2 + D3 (β, 95%CI, P value: 0.030, 0.016–0.044, < 0.01) subgroups, dietary theobromine and DSST were also associated.

To further analyze any non-linear associations, we conducted a curve fitting analysis between theobromine intake and cognitive performance. A non-linear association was found, as presented in Supplementary Fig. 3.

Discussion

In this study, we found a linear association between daily theobromine intake and DSST score, an indicator of execution ability, in a representative old American population. However, dietary theobromine intake was not significantly associated with the CERAD-immediate/delayed recall score and animal fluency score.

Previous studies have explored different diet patterns affecting cognitive function. Fernández-Fernández et al. (34) reported that an LMN diet, mainly composed of theobromine, could enhance cognitive reserve function in mice. One of the active components of chocolate is methylxanthine, of which theobromine is the main constituent. A randomized controlled trial (RCT) focusing on the psycho-pharmacologically of methylxanthines showed a protective effect on cognitive function (35). In a Portuguese prospective cohort study, 531 participants aged ≥ 65 years with normal cognitive function were followed for a median of 48-month to detect the association of chocolate intake and cognition impairment as measured by the Mini-Mental State Examination (4). In this study, researchers reported that long-term chocolate intake was inversely associated with cognitive decline. Another RCT in Japan also investigated the effect of chocolate intake on cognitive function (5). The intervention group was received dark chocolate daily for 30 days. The modified Stroop color word test and digital cancellation test were conducted to test the association between dark chocolate intake and cognitive function, finding that dark chocolate has a beneficial role in cognitive function.

We selected a large, representative elderly American population to further study the association between dietary theobromine and cognitive performance, finding a significant association between daily theobromine intake and DSST score. However, Mitchell et al. reported non-effect of theobromine (700 mg) alone or combination of theobromine (700 mg) and caffeine (120 mg) on DSST scores in 29 female healthy participants (36). In our study, 1000 mg/d theobromine intake was significantly associated with improvement in DSST score, from 4 to 15. Thus, a higher theobromine intake and a larger study sample size might be necessary to observe a positive association between dietary theobromine and DSST scores.

Islam et al. (7) reported that theobromine could improve the working memory of rats through the CaMKII/CREB/BDNF pathway. DSST is a working memory task that reflects execution ability. Thus, more studies will be required to study whether dietary theobromine intake could exert cognitive protection through similar mechanisms.

There are several limitations to our study. First, owing to the intrinsic limitations of the cross-sectional design, our study cannot conclude a causal association between theobromine intake and cognitive performance. Rigorous, prospective cohort studies or RCTs will be required to validate our results. Second, we excluded participants with unavailable daily dietary data or incomplete cognitive test scores, which could have biased our findings. In Supplementary Table 1, we compare the basic characteristics of included and excluded participants, finding that the majority were balanced between these two groups. Third, because of the questionnaire design, we could not analyze side effects related to theobromine intake, such as heart rate and blood pressure. Thus, we cannot estimate the negative impact of theobromine intake. Further research on the use of theobromine in older adults is warranted.

Conclusions

Daily theobromine intake was associated with cognitive performance in a large national representative elderly population. However, further research is needed in order to corroborate our findings.

Abbreviations

NAHNES, National Health and Nutrition Examination Survey

BMI, Body Mass Index

CERAD, Consortium to Establish a Registry for Alzheimer's Disease

DSST, Digit symbol substitution test

RCT, randomized controlled trial

CaMKII, Calcium Calmodulin Dependent Protein Kinase II

CREB, cyclic AMP response element (CRE)-binding protein

BDNF, Brain-Derived Neurotrophic Factor

Declarations

All authors declared no conflict of interest in this study.

Ethics approval and consent to participate

National Center for Health Statistics institutional review board (NCHS IRB/ERB) approved ethic protocol of 2011-2014 NHANES survey (NCHS IRB/ERB Protocol #2011-17).

Consent for publication Not applicable

Availability of data and materials

The dataset(s) supporting the conclusions of this article are available in the NHANES 2011-2012 and 2013-2014 repository in https://wwwn.cdc.gov/nchs/nhanes/Default.aspx.

Competing interests

All authors have no competing interest.

Funding

No funding.

Authors' contributions

Jie Liu, Li Jie Gao, designed the study, Li Jie Gao, Chao Hua Cui, Zheng Zhou Yuan, Wen Jing Ge, Qian Liu, and Jie Li, collected and cleaned the data, Li Jie Gao analyzed the data, Li Jie Gao and Jie Liu analyzed and interpreted the result, Li Jie Gao Na Liu, and Chun Yan Lei written the article. All authors reviewed this manuscript.

Acknowledgements

Not applicable.

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