Age-dependent decline of association between obesity and mortality: a systematic review and meta-analysis

Objective: It is debatable if the strength of obesity-mortality association depends on age. The objective of this study was to investigate the influence of age on the obesity-mortality association in men and women, and to assess if adjusting for major confounding factors altered the age-dependent trend of the obesity-mortality association.

Design and methods: Articles were identified by searches of PubMed through 15 August 2013. Twenty studies which reported two or more age-specific effect estimates were identified. A random-effect approach was applied to estimate pooled effect sizes for different age groups.

Results: There was a significant heterogeneity among studies within each age group in the effect estimates for the association between obesity and mortality. The pooled hazard ratio estimates decreased with increasing age from 1.59 (95% confidence interval, 1.46-1.72) for men and 1.60 (1.49-1.72) for women under 35 years to 1.11 (1.08-1.15) for men and 1.11 (1.09-1.14) for women 75 years or older. On average, the effect estimate was decreased by about 10% with every 10 years increase in age.

Conclusions: Adjusting for known confounding factors of smoking, pre-existing illness, hypertension and diabetes has little impact on the age-dependent decline trend of the obesity-mortality association. Therefore, the strength of the association between obesity and mortality weakens with increasing age.