Trajectory of body shape in early and middle life and all cause and cause specific mortality: results from two prospective US cohort studies

Abstract

Objective: To assess body shape trajectories in early and middle life in relation to risk of mortality.

Design: Prospective cohort study.

Setting: Nurses' Health Study and Health Professionals Follow-up Study.

Population: 80 266 women and 36 622 men who recalled their body shape at ages 5, 10, 20, 30, and 40 years and provided body mass index at age 50, followed from age 60 over a median of 15-16 years for death.

Main outcome measures: All cause and cause specific mortality.

Results: Using a group based modeling approach, five distinct trajectories of body shape from age 5 to 50 were identified: lean-stable, lean-moderate increase, lean-marked increase, medium-stable/increase, and heavy-stable/increase. The lean-stable group was used as the reference. Among never smokers, the multivariable adjusted hazard ratio for death from any cause was 1.08 (95% confidence interval 1.02 to 1.14) for women and 0.95 (0.88 to 1.03) for men in the lean-moderate increase group, 1.43 (1.33 to 1.54) for women and 1.11 (1.02 to 1.20) for men in the lean-marked increase group, 1.04 (0.97 to 1.12) for women and 1.01 (0.94 to 1.09) for men in the medium-stable/increase group, and 1.64 (1.49 to 1.81) for women and 1.19 (1.08 to 1.32) for men in the heavy-stable/increase group. For cause specific mortality, participants in the heavy-stable/increase group had the highest risk, with a hazard ratio among never smokers of 2.30 (1.88 to 2.81) in women and 1.45 (1.23 to 1.72) in men for cardiovascular disease, 1.37 (1.14 to 1.65) in women and 1.07 (0.89 to 1.30) in men for cancer, and 1.59 (1.38 to 1.82) in women and 1.10 (0.95 to 1.29) in men for other causes. The trajectory-mortality association was generally weaker among ever smokers than among never smokers (for all cause mortality: P for interaction <0.001 in women and 0.06 in men). When participants were classified jointly according to trajectories and history of type 2 diabetes, the increased risk of death associated with heavier body shape trajectories was more pronounced among participants with type 2 diabetes than those without diabetes, and those in the heavy-stable/increase trajectory and with a history of diabetes had the highest risk of death.

Conclusions: Using the trajectory approach, we found that heavy body shape from age 5 up to 50, especially the increase in middle life, was associated with higher mortality. In contrast, people who maintained a stably lean body shape had the lowest mortality. These results indicate the importance of weight management across the lifespan.

Fig 1 Trajectories of body shape by age in women (top) and men (bottom). Mean body shape levels on y axis were estimated from trajectory models. Mean body mass index (BMI) at age 50 is shown for each trajectory group

Fig 2 Joint association of trajectories of body shape and history of type 2 diabetes with risk of all cause (top), cardiovascular (middle), and cancer mortality (bottom) among never smokers. Lean-moderate increase and medium-stable/increase groups were combined as “lean/medium-moderate increase” group owing to small number of cases. Multivariable Cox proportional hazards model was used to calculate hazard ratio within each cohort after adjustment for same set of covariates as in tables 2 and 3. Participants were categorized into eight groups according to trajectories and history of type 2 diabetes, with those in lean-stable group and without history of type 2 diabetes as reference. Pooled results from both cohorts are shown here. P values for interaction were calculated from likelihood ratio test with three degrees of freedom by comparing model with product terms between diabetic history (binary) and trajectory groups (indicator variables for three non-reference groups) with model without these terms. P value for interaction for each individual trajectory group was also calculated by Wald test. For all cause mortality, individual P values for interaction were 0. 28 for lean/medium-moderate increase group, 0.09 for lean-marked increase group, and 0.04 for heavy-stable/increase group; corresponding P values for cardiovascular mortality were 0.21, 0.16, and 0.59 and those for cancer mortality were 0.64, 0.34, and 0.01