Relationship between weight-adjusted waist index and handgrip strength in adults aged 50 and older in the United States: a cross-sectional study.

DOI: https://doi.org/10.21203/rs.3.rs-2792151/v1

Abstract

Background: Body muscle mass and strength have established links with obesity, but the association between weight-adjusted waist index (WWI) and combined handgrip strength remains largely unexplored. This study aims to examine the relationship between combined grip strength and WWI in individuals aged 50 and above.

Methods: We utilized data from the National Health and Nutrition Examination Survey (NHANES) from 2011 and 2014. Multivariate logistic and linear regression models, generalized additive models, and fitted smoothing curves were employed to investigate the association between WWI and combined grip strength.

Results: Our analysis of 4,179 eligible participants demonstrated a significant inverse relationship between grip strength and WWI. Subgroup analysis stratified by gender revealed a significant negative association between combined grip strength and WWI for both men and women. However, a saturation effect was observed in men, with an inflection point at 13.40 (cm/√kg).

Conclusion: The present study highlights a negative association between combined grip strength and WWI in individuals over 50 years of age, with the relationship being particularly influenced by men (inflection point: 13.40 cm/√kg).

Introduction

Obesity has emerged as a global health concern, affecting approximately half a billion adult men and women worldwide[1]. In the United States, over 32% of adults are reported to be obese[2]. Recent studies have established connections between obesity and various health conditions, such as type II diabetes[3], hypertension[4], dyslipidemia[5], and sleep apnea syndrome[6].

The weight-adjusted waist index (WWI), along with body mass index (BMI) and waist circumference (WC), has been employed as a measure of obesity. Despite BMI's widespread acceptance, it has certain limitations, such as an inability to differentiate between visceral and other types of fat and less accurate measurements of body fat in older adults compared to younger individuals[7]. Park et al[8]. first proposed WWI as an index to assess central obesity and quantify the muscle-to-fat content ratio.

Sarcopenia, the age-related decline in muscle mass and strength, has become a significant socioeconomic concern[9]. Recent research has found that up to 10% of individuals over 60 years old suffer from sarcopenia, underscoring the age-associated decline in muscular strength[10]. Men were found to lose more muscle mass than women in both sex groups, with the extent of muscle loss strongly correlated with activity levels[11, 12]. Sarcopenia diagnosis and muscle mass measurement typically involve magnetic resonance imaging (MRI), computed tomography (CT), dual-energy X-ray absorptiometry (DXA), and bioelectrical impedance analysis (BIA)[13]. Reduced grip strength, associated with muscle strength, can lead to falls[14], fractures[15], mental disorders[16], and an increased risk of diabetes[17].It has initially been shown that WWI has a significant association with the incidence of cardiovascular disease[18], the degree of abdominal aortic calcification[19], and the rate of urinary protein excretion[20]. Although previous research has demonstrated a relationship between obesity and handgrip strength, the association between WWI and combined grip strength remains understudied.

This study, using data from the National Health and Nutrition Examination Survey (NHANES), aims to investigate the relationship between WWI and combined grip strength in Americans aged 50 and above.

Materials And Methods

Data for this cross-sectional study were sourced from the National Health and Nutrition Examination Survey (NHANES), an ongoing survey initiated in 1999 that employs a multi-stage, stratified design to assess the health and nutritional status of the American population. Conducted by the National Center for Health Statistics (NCHS), NHANES collects data from lab tests, examinations, and questionnaires pertaining to various medical conditions and physical ailments. The NCHS Research Ethics Review Committee approved all NHANES study protocols, with informed consent obtained from all participants. This study utilized the NHANES dataset from 2011 to 2014, focusing on American adults aged 50 or older. Out of 19,931 eligible adults, exclusions were made for missing WWI data (3,085), missing combined grip strength data (2,666), age under 50 (9,725), missing arthritis data (16), missing diabetes data (250), and missing hypertension data (10), resulting in a final sample size of 4,179(Fig .1).

The extent of obesity was determined using the weight-adjusted waist index (WWI), calculated as waist circumference (cm) / √body weight (kg). WWI served as the exposure factor in this study. Body weight (kg) was measured using a digital scale with 0.1 kg precision while participants wore an MEC measuring suit. Waist circumference (cm) was measured using a telescopic tape measure, with a single decimal place retained. Anthropometric assessments were conducted by professional health technicians at the Mobile Examination Center (MEC), with the data routinely tested and evaluated. Combined grip strength (kg) was measured using a dynamometer, with three maximum effort trials for each hand and a 60-second interval between trials. The sum of the maximum grip strength values of both hands was used as the combined grip strength value.

Potential confounding factors influencing the relationship between WWI and combined grip strength were considered, including age, sex, race, education, household income ratio, BMI, weight, waist circumference, alcohol consumption within the past 12 months, sedentary time, total cholesterol (TC), triglycerides (TG), presence of diabetes, arthritis, and hypertension. The computation of these variables can be found on the NHANES website (https://www.cdc.gov/nchs/nhanes/).

Statistical Analysis

To examine the implications of combined grip strength quartiles, continuous and categorical variables were analyzed using weighted Student's t-tests and weighted chi-square tests. Frequency, mean, percentage, and standard error were utilized to describe essential demographic characteristics, as well as combined grip strength and WWI quartiles. The linear relationship between WWI and the sum of grip strength across subgroups was examined using weighted multiple logistic regression. Subgroup analysis assessed the consistency of the correlation between WWI and combined grip strength across populations. The generalized additive model and smooth curve fitting were employed to address the nonlinear relationship between combined grip strength and WWI. A piecewise linear regression model was used to fit each interval and determine threshold effect values, with the study investigating possible inflection points between WWI and combined grip strength. Package R (http://www.r-project.org)andEmpowerStats (http://www.empowerstats.com) were used for all analyses, with P < 0.05 considered statistically significant.

Results

A total of 4,179 American individuals aged 50 or older participated in this study, with 49.25% male, 50.75% female, and 44.03% identifying as white. The average age of participants was 64 years. The weight-adjusted waist index (WWI) ranged from 9.02 to 14.79 (cm/√kg), with a mean value of 11.38 (cm/√kg). The mean combined grip strength was 64.4 (kg). The quartile range of combined grip strength was as follows: Q1: ≤49.5 kg, Q2: 49.6–61 kg, Q3: 61.1–79.1 kg, and Q4: ≥79.2 kg. As combined grip strength quartiles increased, WWI gradually decreased, with this relationship being statistically significant (p < 0.001). Participants in the first quartile, compared to those in the highest quartile, were more likely to be female, have a lower body weight, belong to a non-black race, have higher total cholesterol levels, be more educated, have abstained from alcohol for at least a year, and have been diagnosed with high blood pressure, arthritis, or diabetes (Table 1).(On page 21)

The unadjusted model showed a strong and negative association between WWI and combined grip strength (β = -9.89, 95% CI: -10.67 to -9.11, p < 0.001). Even after accounting for all relevant covariates, the fully adjusted model demonstrated a significant inverse relationship between WWI and combined grip strength (β = -5.11, 95% CI: -5.74 to -4.49, p < 0.001), with grip strength decreasing by 5.11 (kg) for every unit increment in WWI. When stratifying WWI, results indicated that lower grip strength was associated with higher WWI levels. Participants in the T3 group exhibited grip strength measurements that were 7.25 kg lower than those in the T1 group (β = 7.25, 95% CI: -8.32 to -6.17, p < 0.001) (Table 2).(On page 23)

Subgroup analyses based on gender and arthritis status revealed that these factors influenced the relationship between WWI and combined grip strength (p for trend < 0.05), while the relationship remained stable for the remaining subgroups (Table 3)(On page 24).

The smoothed curves of WWI and combined grip strength were fitted, confirming the negative linear correlation between the two variables (Fig.2).

A smoothed curve subcomponent analysis was conducted based on gender (Fig.3). Furthermore, the study demonstrated that the WWI and combined grip strength smoothing curves in males exhibited a saturation threshold and an inflection point of 13.40 (cm/√kg) (Table 4)(On page 25).

Discussion

This study is the first to use NHANES data to investigate the association between WWI and combined grip strength, examining data from 4,179 eligible subjects. A significant inverse relationship between WWI and combined grip strength was observed, with a saturation effect for grip strength in men and WWI at an inflection point of 13.40 (cm/√kg). The subgroup analysis revealed notable differences between gender groups.

WWI, a novel index for measuring obesity, is calculated as waist circumference divided by the square root of body weight (cm/√kg) and was initially developed by Park et al[8]. As a reflection of central obesity, WWI has been linked to various health conditions, including heart failure[21], abdominal aorta calcification[19], hyperuricemia[22], and others. Our results demonstrate that a higher WWI is associated with lower grip strength, indicating that weakened muscle strength can adversely affect sarcopenia. Thus, WWI may help diagnose and manage sarcopenia by responding to muscle strength and rating the degree of muscle loss.

A significant correlation between higher WWI and lower combined grip strength was found in this study. Obesity has also been shown to be negatively correlated with grip strength in a meta-analysis by Hsu et al[23]. which used BMI to assess obesity. As both BMI and WWI are indicators of obesity, their study provides support for our findings. The inclusion of arthritis as a covariate and subgroup analysis in this project was based on a cohort study of 300 patients with arthritis and grip strength, where the severity of thumb arthritis was significantly negatively associated with grip strength (β = -0.79 ,95% CI -1.10- -0.49,p༜0.05)[24]. Our study suggests that patients with arthritis are more likely to have lower combined grip strength and that arthritis status alters the association between WWI and grip strength. Furthermore, our study reveals that combined grip strength in men is no longer significantly correlated with higher WWI when WWI is greater than 13.40 (cm/√kg). The correlation between grip strength and WWI in women remained consistently negative. Factors such as hormone levels[25], dietary patterns [26], fat distribution[27], and others can account for gender differences. A prospective study with a larger sample size is required to confirm the relationship between combined grip strength in men and women and WWI.

To our knowledge, few clinical studies have examined the association between WWI and muscle strength in US adults. In a cross-sectional study in Korea, researchers found that among 602 older adults aged over 65, WWI was negatively associated with muscle mass and positively associated with adiposity[28]. Additionally, an NHANES cross-sectional study revealed a negative association between WWI and abdominal muscle mass in patients with atherosclerosis[29]. Kim et al[30]. found that different body measurements had the strongest correlation with WWI in the evaluation of sarcopenic obesity in a descriptive clinical study. These studies primarily focused on WWI and muscle mass. Previous research has suggested that the negative effect of obesity on muscle strength is present in both adolescents and the elderly and that grip strength is negatively associated with the risk of obesity prevalence in men[31, 32]. A cross-sectional study involving 423 Spanish children aged 11 examined the relationship between physical obesity and muscle movement, discovering that obese children performed worse on tests such as jumping height and running speed[33]. All three studies assessed obesity using BMI, WC, and other indicators, and none used WWI as an assessment indicator.

Based on previous research, there are several plausible explanations for the mechanisms underlying the negative association between WWI and muscle strength. Satellite cells (SC) play a crucial role in promoting skeletal muscle growth and development. However, their functions are adversely affected by fatty diets and obesity. A cellular study demonstrated that excessive glucose and fat intake impairs SC cell function, consequently impacting skeletal muscle mass and strength[34]. Additionally, an animal experiment showed that muscle hypertrophy was linked to reduced fat and blood glucose levels when mice were fed a high-fat, high-sugar diet, followed by rapid type II glycolysis of muscle fibers [35]. Obesity also contributes to increased levels of non-esterified fatty acid (NEFA), which in turn upregulates various inflammatory factors such as tumor necrosis factor-alpha (TNF-α), interleukin-1 (IL-1), and interleukin-6 (IL-6) through adipokine regulation or Toll-like receptor activation, resulting in chronic inflammation[36, 37]. These cytokines activate the ubiquitin-proteasome system (UPS), thereby increasing the likelihood of muscle wasting [38]. These findings illustrate the negative correlation between obesity and grip strength and indirectly reflect the mechanism of association between WWI, as an obesity indicator, and grip strength.

One of the strengths of this study is its foundation on the extensive NHANES database, which is more representative of the study population. Furthermore, we were the first research team to investigate the relationship between WWI and combined grip strength, identifying a negative association within the WWI range and combined grip strength. Stratified subgroup analysis was also conducted for factors such as gender. However, the study has some limitations. Firstly, the project did not analyze and study all age groups, focusing instead on the association between grip strength and WWI in Americans over 50. Secondly, it is essential to acknowledge that the cross-sectional nature of this study limits our ability to establish causality. A considerable number of prospective trials must be conducted to confirm our findings and demonstrate causality.

Conclusions

Our study uncovered a negative association between combined grip strength and WWI in individuals over 50, with men influencing this relationship (inflection point: 13.40 cm/√kg). The WWI, as a validated index for assessing obesity, may serve as a novel tool for evaluating and managing muscle strength in clinical practice.

Abbreviations

WWI        

Weight-adjusted Waist Index

BMI

Body Mass Index

WC

Waist Circumference

Declarations

Acknowledgments

Thank Jinxiao Cheng and Ying Wang for their constructive suggestions.

Authors’ contributions

L.Z,L,W are corresponding authors. Q.W,G.L designed the study. G.L,X.W took part in data collection and preparation. G.L,L.W,L.Z analysed the data. R.X contributed to the interpretation and categorisation of the data. G.L drafted the manuscript, with all authors providing critical revision and approving the final manuscript.

Funding 

This study supported by the Interdisciplinary Innovative Talents Foundation from Renmin Hospital of Wuhan University(Project No.:JCRCYR-2022-001).

Availability of data and materials

Publicly available datasets were analyzed in this study. This data can be found here: www.cdc.gov/nchs/nhanes/.Package R (http://www.r-project.org)andEmpowerStats (http://www.empowerstats.com) were used for all analyses.

Ethics approval and consent to participate

The NCHS Research Ethics Review Committee approved all NHANES study protocols, with informed consent obtained from all participants.

Consent for publication

Not application.

Competing interests

The authors declares that they have no competing interests.

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Tables

Table 1. Weighted characteristics of the study population based on combined grip 

Combined grip strength(kg) 

Q1

(≤49.5)

Q2(49.6-61)

Q3(61.1-79.1)

Q4

(≥79.2)

P-value

Age(years)

68.66 ± 9.23

63.53 ± 9.02

63.31 ± 9.24

60.52 ± 7.72

<0.001

Gender%

 

 

 

 

<0.001

Male

8.39

23.25

65.97

98.85

 

Female

91.61

76.75

34.03

1.15

 

Race%

 

 

 

 

<0.001

Mexican American

10.70

8.80

9.44

9.16

 

Other Hispanic

13.31

11.29

8.58

6.39

 

Non-Hispanic White

47.64

44.78

40.51

43.23

 

Non-Hispanic Black 

15.14

22.58

29.84

31.39

 

Other Races Including Multi-Racial

 

13.21

12.54

11.63

9.83

 

The ratio of family income to poverty

2.29 ± 1.49

2.63 ± 1.59

2.60 ± 1.56

2.90 ± 1.60

<0.001

Weight(kg,mean±SD)

70.64 ± 17.70

77.02 ± 17.86

83.14 ± 18.78

91.20 ± 20.12

<0.001

BMI(kg/m2,mean±SD)

28.60 ± 6.83

29.30 ± 6.77

29.27 ± 6.53

29.36 ± 5.92

0.002

Waist circumference(cm,mean±SD)

98.07 ± 14.89

100.07 ± 14.62

102.83 ± 15.23

105.08 ± 15.38

<0.001

Weight adjusted waist index(cm/√kg,mean±SD)

11.73 ± 0.75

11.45 ± 0.69

11.31 ± 0.68

11.03 ± 0.65

<0.001

Combined grip strength(kg,mean±SD)

40.71 ± 6.66

54.97 ± 3.25

69.34 ± 5.30

92.27 ± 10.24

<0.001

Minutes sedentary activity(min,mean±SD)

386.90 ± 197.58

380.19 ± 193.59

398.45 ± 197.59

390.89 ± 194.40

0.195

Total cholesterol(mg/dl,mean±SD)

5.18 ± 1.09

5.18 ± 1.12

4.95 ± 1.07

4.91 ± 1.06

<0.001

Triglyceride(mg/dl,mean±SD)

123.74 ± 49.77

123.74 ± 49.05

124.46 ± 62.63

126.00 ± 54.23

0.152

Educational level(%)

 

 

 

 

<0.001

<12years

32.31

21.91

25.74

22.71

 

>12years

67.99

78.09

74.26

77.29

 

Have ever drunk alcohol for the past 12 months(%)

 

 

 

 

0.853

No

23.53

22.87

23.36

22.04

 

Yes

76.47

77.13

76.64

77.96

 

High blood pressure(%)

 

 

 

 

<0.001

Yes

62.58

51.87

52.14

49.81

 

No

37.42

48.13

47.86

50.19

 

Diabetes(%)

 

 

 

 

0.002

Yes

24.98

21.63

20.40

18.32

 

No

75.02

78.37

79.60

81.68

 

Arthritis(%)

 

 

 

 

<0.001

Yes

56.61

45.17

36.03

29.58

 

No

43.39

54.83

63.97

70.42

 

strength quartiles Mean ± SD for continuous variables ;the P value was calculated by the weighted linear regression model(%) for categorical variables ;the P value was calculated by the weighted chi-square test WWI. 

Table 2. Multivariate logistic regression models of combined grip strength with WWI

 

Model1β(95%CI)

Model2β(95%CI)

Model3β(95%CI)

 

P VALUE

P VALUE

P VALUE

Weight-adjusted waist index

-9.89(-10.67,-9.11)

-3.29(-3.85,-2.74)

-5.11(-5.74,-4.49)

 

<0.0001

<0.0001

<0.0001

Tertile analysis of weight-adjusted waist index

 

 

 

T1

Reference

Reference

Reference

T2

-6.82(-8.24,-5.39)

-1.82(-2.76,-0.88)

-3.05(-3.99,-2.11)

 

<0.0001

0.0001

<0.0001

T3

-16.07(-17.49,-14.65)

-5.03(-6.02,-4.05)

-7.25(-8.32,-6.17)

 

<0.0001

<0.0001

<0.0001

P for trend

<0.0001

<0.0001

<0.0001

Model1:no covariates were adjusted. Model 2: age, gender, and race were adjusted. Model 3:age, gender, race, educational level , BMI, family income-to-poverty ratio, have ever drunk alcohol for the past 12 months, diabetes status, high blood pressure status, arthritis status , minutes of sedentary activity, total cholesterol and triglyceride were adjusted. 

Table 3. Subgroup analysis of the relationship between WWI and combined grip strength

 

Model1β(95%CI)

Model2β(95%CI)

Model3β(95%CI)

 

P VALUE

P VALUE

P VALUE

Gender

 

 

 

Male

-8.69(-9.56,-7.83)

-4.94(-5.77,-4.12)

-9.81(-10.71,-8.91)

Female

<0.0001

<0.0001

<0.0001

Female

-4.07(-4.86,-3.29)

-1.91(-2.64,-1.19)

-2.33(-3.09,-1.58)

P for trend

<0.0001

<0.0001

<0.0001

Arthritis(yes or no)

 

 

 

yes

-8.99(-10.19,-7.79)

-3.04(-3.86,-2.23)

-4.39(-5.26,-3.51)

 

<0.0001

<0.0001

<0.0001

no

-9.25(-10.28,-8.21)

-3.31(-4.02,-2.59)

-3.31(-4.02,-2.59)

 

<0.0001

<0.0001

<0.0001

P for trend

0.7532

0.6228

0.0072

High blood pressure(yes or no)

 

 

 

yes

-10.21(-11.29,-9.13)

-3.59(-4.33,-2.85)

-5.28(-6.06,-4.51)

 

<0.0001

<0.0001

<0.0001

no

-9.35(-10.52,-8.18)

-3.10(-3.90,-2.31)

-4.91(-5.73,-4.08)

 

<0.0001

<0.0001

<0.0001

P for trend

0.2885

0.3592

0.4580

Diabetes(yes or no)

 

 

 

yes

-10.98(-12.73,-9.23)

-3.83(-5.04,-2.62)

-5.83 (-7.03,-4.63)

 

<0.0001

<0.0001

<0.0001

no

-9.74(-10.63,-8.84)

-2.93(-3.56,-2.30)

-4.96 (-5.64,-4.29)

 

<0.0001

<0.0001

<0.0001

P for trend

0.2155

0.1876

0.1851

Model1:no covariates were adjusted. Model 2: age, gender, and race were adjusted. Model 3:age, gender, race, educational level , BMI, family income-to-poverty ratio, have ever drunk alcohol for the past 12 months, diabetes status, high blood pressure status, arthritis status , minutes of sedentary activity, total cholesterol and triglyceride were adjusted. 

Table 4. Threshold effect analysis of WWI on combined grip strength in men using the two-piecewise linear regression model.

Combined grip strength

Adjusted β(95%CI) p value

Men

 

Fitting by the standard linear model

-9.73 (-10.88, -8.58)

Fitting by the two-piecewise linear model

 

Inflection point

13.40

Weight adjusted waist index<13.40(cm/√kg)

-9.91 (-11.07, -8.75)

 

<0.0001

Weight adjusted waist index>13.40(cm/√kg)

9.79 (-9.35, 28.93)

 

0.3160

Log likelihood ratio

0.044

Age, gender, race, educational level, BMI, family income-to-poverty ratio, have ever drunk alcohol for the past 12 months, diabetes status, high blood pressure status, arthritis status, minutes of sedentary activity, total cholesterol and triglyceride were adjusted.