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. 2022 Oct 24;20(1):404.
doi: 10.1186/s12916-022-02596-7.

Relationship of body mass index with frailty and all-cause mortality among middle-aged and older adults

Kulapong Jayanama  1   2 , Olga Theou  2   3 , Judith Godin  2 , Andrea Mayo  2 , Leah Cahill  4   5 , Kenneth Rockwood  6   7
Affiliations

Relationship of body mass index with frailty and all-cause mortality among middle-aged and older adults

Kulapong Jayanama et al. BMC Med. .

Abstract

Background: Parallel to growth of aging and obese populations, the prevalence of metabolic diseases is rising. How body mass index (BMI) relates to frailty and mortality across frailty levels is controversial. We examined the associations of high BMI with frailty and mortality and explored the effects of percent body fat on these associations.

Methods: We included 29,937 participants aged ≥50 years from the 2001-2006 National Health and Nutrition Examination Survey (NHANES) cohorts (N=6062; 53.7% females) and from wave 1 (2004) of Survey of Health, Ageing and Retirement in Europe (SHARE) (N=23,875; 54% females). BMI levels were categorized as: normal: 18.5-24.9 kg/m2, overweight: 25.0-29.9, obese grade 1: 30.0-34.9, and obese grade 2 or 3: >35.0. A frailty index (FI) was constructed excluding nutrition-related items: 36 items for NHANES and 57 items for SHARE. We categorized the FI using 0.1-point increments: FI ≤ 0.1 (non-frail), 0.1 < FI ≤ 0.2 (very mildly frail), 0.2 < FI ≤ 0.3 (mildly frail), and FI > 0.3 (moderately/severely frail). Percent body fat was measured using DXA for NHANES participants. All-cause mortality data were obtained until 2015 for NHANES and 2017 for SHARE to estimate 10-year mortality risk. All analyses were adjusted for age, sex, educational, marital, employment, and smoking statuses.

Results: Mean age of participants was 63.3±10.2 years for NHANES and 65.0±10.0 years for SHARE. In both cohorts, BMI levels ≥25 kg/m2 were associated with higher frailty, compared to normal BMI. In SHARE, having a BMI level greater than 35 kg/m2 increased mortality risk in participants with FI≤0.1 (HR 1.31, 95%CI 1.02-1.69). Overweight participants with FI scores >0.3 were at lower risk for mortality compared to normal BMI [NHANES (0.79, 0.64-0.96); SHARE (0.71, 0.63-0.80)]. Higher percent body fat was associated with higher frailty. Percent body fat significantly mediated the relationship between BMI levels and frailty but did not mediate the relationship between BMI levels and mortality risk.

Conclusions: Being overweight or obese is associated with higher frailty levels. In this study, we found that being overweight is a protective factor of mortality in moderately/severely frail people and obesity grade 1 may be protective for mortality for people with at least a mild level of frailty. In contrast, obesity grades 2 and 3 may be associated with higher mortality risk in non-frail people. The relationship between BMI and frailty is partially explained by body fat.

Keywords: Body composition; Body mass index; Frailty; Mortality; Obese; Percent body fat.

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Conflict of interest statement

Kenneth Rockwood has asserted copyright of the Clinical Frailty Scale through Dalhousie University’s Industry, Liaison, and Innovation Office. Use is free for education, research, and not-for-profit health care. Users agree not to change or commercialize the scale. In addition to academic and hospital appointments, KR is co-founder of Ardea Outcomes, which (as DGI Clinical) in the last 3 years has contracts with pharma and device manufacturers (Danone, Hollister, INmune, Novartis, Takeda) on individualized outcome measurement. In 2020, he attended an advisory board meeting with Nutricia on dementia and chaired a Scientific Workshop & Technical Review Panel on frailty for the Singapore National Research Foundation. He is the Associate Director of the Canadian Consortium on Neurodegeneration in Aging, itself funded by the Canadian Institutes for Health Research, the Alzheimer Society of Canada, and several other charities.

Other authors declare no potential competing interests.

Figures

Fig. 1
Fig. 1
Relationship between body mass index and frailty. All regression models were adjusted for age, sex, educational level, marital status, employment status, and smoking. Cross-sectional analysis examined the body mass index and frailty index from the NHANES 2001–2006 cohorts and SHARE wave 1. Longitudinal analysis examined the body mass index from SHARE wave 1 and frailty index from SHARE wave 6
Fig. 2
Fig. 2
Relationship between body mass index and 10-year mortality risk, stratified by frailty levels. All regression models were adjusted for age, sex, educational level, marital status, employment status, and smoking
Fig. 3
Fig. 3
Correlation between BMI and percent body fat, stratified by frailty levels. Data from the 2001–2006 cohorts of NHANES
Fig. 4
Fig. 4
Mediating effect of percent body fat on the relationship between body mass index and frailty, using single-mediation regression model by Andrew F. Hayes. * p <0.001. Participant with body mass index 18.5–24.9 kg/m2 as a reference group. The numbers were presented in beta-coefficients (standard error). All regression models were adjusted for age, sex, educational level, marital status, employment status, and smoking. Data from the 2001–2006 cohorts of NHANES
Fig. 5
Fig. 5
Mediating effect of percent body fat on the relationship between body mass index and mortality in participants with FI 0.2–0.3, using the product of coefficients approaches by Mackinnon. *p <0.001. Participants with body mass index 18.5–24.9 kg/m2 as a reference group. Ordinary least squares regression analyses were used to examine the relationship between body mass index and percent body fat. Cox regression analyses were used to examine the relationship of body mass index and percent body fat with mortality risk. The numbers were presented in beta-coefficients (standard error). All regression models were adjusted for age, sex, educational level, marital status, employment status, and smoking. Data from the 2001–2006 cohorts of NHANES
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