Obesity paradox of cardiovascular mortality in older adults in the United States: A cohort study using 1997-2018 National Health Interview Survey data linked with the National Death Index.

Background: Large-scale, population-based investigations primarily investigating the association between body mass index (BMI) and cardiovascular disease (CVD) mortality among older and younger adults in the United States (U.S.) are lacking.

Objective: To evaluate the relationship between BMI and CVD mortality in older (≥65 years) and younger (<65 years) adults and to identify the nadir for CVD mortality.

Design: This cohort study used serial cross-sectional data from the 1997 to 2018 National Health Interview Survey (NHIS) linked with the National Death Index. NHIS is an annual nationally representative household interview survey of the civilian noninstitutionalized U.S.

Setting: Residential units of the civilian noninstitutionalized population in the U.S.

Participants: The target population for the NHIS is the civilian noninstitutionalized U.S. population at the time of the interview. We included all adults who had BMI data collected at 18 years and older and with mortality data being available. To minimize the risk of reverse causality, we excluded adults whose survival time was ≤2 years of follow-up after their initial BMI was recorded and those with prevalent cancer and/or CVD at baseline.

Methods: We used the BMI record obtained in the year of the NHIS survey. Total CVD mortality used the NHIS data linked to the latest National Death Index data from the survey inception to December 31, 2019. We performed multivariable Cox proportional hazards regression models to estimate adjusted hazard ratios (aHRs) and 95 % confidence intervals (CIs).

Results: The study included 425,394 adults; the mean (SD) age was 44 (16.7) years. During a median follow-up period of 11 years, 12,089 CVD-related deaths occurred. In older adults, having overweight was associated with a lower risk of CVD mortality (aHR 0.92 [95 % CI, 0.87-0.97]); having class I obesity (1.04 [0.97-1.12]) and class II obesity (1.12 [1.00-1.26]) was not significantly associated with an increased CVD mortality; and having class III obesity was associated with an increased risk of CVD mortality (1.63 [1.35-1.98]), in comparison with adults who had a normal BMI. Yet, in younger adults, having overweight, class I, II, and III obesity was associated with a progressively higher risk of CVD mortality. The nadir for CVD mortality is 28.2 kg/m in older adults and 23.6 kg/m in younger adults.

Conclusion: This U.S. population-based cohort study highlights the significance of considering age as a crucial factor when providing recommendations and delivering self-care educational initiatives for weight loss to reduce CVD mortality.