Associations between body mass index and all-cause mortality: A systematic review and meta-analysis

Fasting insulin and c-reactive protein confound the association between mortality and body mass index. An increase in fat mass may mediate the associations between hyperinsulinemia, hyperinflammation, and mortality. The objective of this study was to describe the average associations between body mass index and the risk of mortality and to explore how adjusting for fasting insulin and markers of inflammation might modify the association of BMI with mortality. MEDLINE and EMBASE were searched for studies published in 2020. Studies with adult participants where BMI and vital status was assessed were included. BMI was required to be categorized into groups or parametrized as non-first order polynomials or splines. All-cause mortality was regressed against mean BMI squared within seven broad clinical populations. Study was modeled as a random intercept. beta coefficients and 95% confidence intervals are reported along with estimates of mortality risk by BMIs of 20, 30, and 40 kg/m(2). Bubble plots with regression lines are drawn, showing the associations between mortality and BMI. Splines results were summarized. There were 154 included studies with 6,685,979 participants. Only five (3.2%) studies adjusted for a marker of inflammation, and no studies adjusted for fasting insulin. There were significant associations between higher BMIs and lower mortality risk in cardiovascular (unadjusted beta -0.829 [95% CI -1.313, -0.345] and adjusted beta -0.746 [95% CI -1.471, -0.021]), Covid-19 (unadjusted beta -0.333 [95% CI -0.650, -0.015]), critically ill (adjusted beta -0.550 [95% CI -1.091, -0.010]), and surgical (unadjusted beta -0.415 [95% CI -0.824, -0.006]) populations. The associations for general, cancer, and non-communicable disease populations were not significant. Heterogeneity was very large (I-2 >= 97%). The role of obesity as a driver of excess mortality should be critically re-examined, in parallel with increased efforts to determine the harms of hyperinsulinemia and chronic inflammation.

Automated summary

The association between mortality and body mass index (BMI) is affected by fasting insulin and c-reactive protein. Increased fat mass may play a mediating role in the relationship between hyperinsulinemia, hyperinflammation, and mortality. This study aims to investigate the average associations between BMI and mortality risk and explore the impact of adjusting for insulin and markers of inflammation on this association.