Body Composition in Late Midlife as a Predictor of Accelerated Age-associated Deficit-accumulation From Late Midlife into Old Age: A Longitudinal Birth Cohort Study

Abstract

Background: Body mass index (BMI) may not be an optimal predictor of frailty as its constituents, lean and fat mass, may have opposite associations with frailty.

Methods: A linear mixed model analysis was performed in the Helsinki Birth Cohort Study (n = 2 000) spanning from 57 to 84 years. A 39-item frailty index (FI) was calculated on three occasions over 17 years. Body composition in late midlife included BMI, percent body fat (%BF), waist-to-hip ratio (WHR), lean mass index (LMI), and fat mass index (FMI).

Results: Mean FI levels increased by 0.28%/year among men and by 0.34%/year among women. Among women, per each kg/m2 higher BMI and each unit higher %BF the increases in FI levels per year were 0.013 percentage points (PP) steeper (95% CI = 0.004, 0.023) and 0.009 PP steeper (95% CI = 0.002, 0.016) from late midlife into old age. Among men, per each 0.1-unit greater WHR the increase in FI levels was 0.074 PP steeper per year (95% CI = -0.0004, 0.148). Cross-sectionally, greater FMI and LMI in late midlife were associated with higher FI levels but the direction of the association regarding LMI changed after adjustment for FMI. The categories "high FMI and high LMI" and "high FMI and low LMI" showed the highest FI levels relative to the category "low FMI and low LMI".

Conclusions: In late midlife, greater adiposity (%BF) among women and abdominal obesity (WHR) among men may predispose to higher levels of frailty from late midlife into old age. Greater lean mass alone may be protective of frailty, but not in the presence of high fat mass.

Keywords: Body composition; Frailty; Life-course; Risk factor.

Figure 1.

Flowchart of participants in the Helsinki Birth Cohort Study.

Figure 2.

(A–C) Mean frailty index levels (FI × 100) as a function of age from late midlife into old age in the Helsinki Birth Cohort Study for body composition variables which were significantly associated with the rate of change in FI levels from late midlife into old age: shown (A) separately for men and women in groups of BMI (<25.0 kg/m², ≥25.0 and ≤30.0 kg/m², >30.0 kg/m²), (B) separately for men and women in groups of percent body fat (%BF) (sex-specific 25th and 75th percentile), (C) separately for men and women in groups of waist-to-hip ratio (WHR) (sex-specific 25th and 75th percentile). Adjusted with smoking, adult socioeconomic status, and their interactions with age. Parametric bootstrap was used to calculate 95% confidence intervals.

Figure 3.

Mean frailty index levels (FI × 100) as a function of age from late midlife into old age in the Helsinki Birth Cohort Study shown in FMI–LMI categories. The cut-off for low/high FMI was 6.29 kg/m² for men and 
9.20 kg/m² for women and the cut-off for low/high LMI was 20.77 kg/m² for men and 17.93 kg/m² for women. Adjusted with smoking, adult socioeconomic status, and their interactions with age. Parametric bootstrap was used to calculate 95% confidence intervals.