Age-Specific Associations Between Adiposity and Mortality in U.S. Adults, 1999-2018

Obesity is a leading risk factor for increased mortality. However, it remains unclear how this relationship varies across different age groups.

The purpose of this study was to evaluate whether the associations between adiposity and mortality are modified by age in a nationally representative sample of U.S. adults.

We analyzed data from 44,041 U.S. adults aged 18 to 79 years from the National Health and Nutrition Examination Survey (1999-2018), linked to mortality data through 2019. Anthropometric measures included body mass index, waist circumference, weight, and waist-to-height ratio. Cox proportional hazards models were used to assess the interaction between age and adiposity on all-cause and cardiovascular mortality, adjusting for demographic, behavioral, and clinical covariates.

Over a median follow-up of 10.1 years, there were 5,019 deaths (1,186 cardiovascular). Significant interactions between age and all 4 adiposity measures were observed (P < 0.05). Associations between adiposity and mortality were strongest among younger adults. For example, each 1-SD increase in body mass index was associated with a cardiovascular mortality HR of 1.49 (95% CI: 1.27-1.77) in adults aged 18 to 49 years, vs 1.15 (95% CI: 0.99-1.32) in those aged 70 to 79 years. Class 3 obesity was associated with a cardiovascular mortality HR of 4.37 (95% CI: 2.01-9.50) in younger adults. Underweight status was also associated with elevated all-cause mortality, particularly among younger individuals (HR: 2.04; 95% CI: 1.24-3.36).

Age significantly modifies the relationship between adiposity and mortality. Younger adults experience greater mortality risks from both obesity and underweight, underscoring the need for early, age-tailored interventions.