People who are, at some point in adulthood, obese or overweight have an increased risk for death due to CVD, cancer and other causes. Examining maximum BMI, as opposed to a single baseline BMI, may reverse the association between excess weight and increased mortality, according to recent findings published in Annals of Internal Medicine.
“Several prior studies have investigated risk for death by using maximum lifetime BMI, and the results. This method is advantageous because it identifies persons who maintained a normal BMI over time as opposed to entering the normal category due to illness-induced weight loss,” Edward Yu, MS, from Harvard T.H. Chan School of Public Health, and colleagues wrote. “However, previous studies assessed maximum weight by recall and analyses were limited to never smokers... [and] information on cause-specific mortality was not reported.”
To investigate the controversial relationship between BMI and mortality, researchers assessed risks for all-cause and cause-specific death associated with overweight and obesity in three previous cohort studies: Nurses’ Health Study I and II and Health Professionals Follow-Up Study. They measured maximum BMI over 16 years of weight history and subsequent mortality for 225,072 participants, then assessed deaths that occurred over a mean of 12 years of follow-up.
The results showed that participants with a maximum BMI in the overweight (HR = 1.06; 95% CI, 1.03-1.08), obese I (HR = 1.24; 95% CI, 1.2-1.29) and obese II (HR = 1.73; 95% CI, 1.66-1.8) categories were at increased risk for all-cause death. The researchers observed a consistent pattern of excess mortality risk with a maximum BMI above the normal rate across all categories regardless of smoking status, sex and age; however, the excess risk was highest among those aged younger than 70 years and never-smokers. They also found that the lowest risk for death occurs among persons with a maximum BMI of 18.5 to 24.9 kg/m2 at all ages. In contrast, when BMI was defined using a single baseline measurement, they saw a significant inverse association between overweight and mortality (HR = 0.96; 95% CI, 0.94-0.99). Maximum overweight was also linked to increased cause-specific death, notably from CVD and coronary heart disease. Participants who had significant drops in weight experienced the greatest risk for death, most likely reflecting unintentional weight loss cause by illness.
“Compared with using BMI data from one baseline questionnaire, use of extended weight histories revealed stronger associations with risk for death and reversed the paradoxical association between overweight and mortality that previous analyses have reported,” Yu and colleagues wrote. “These significant elevations in risk are important from a public health perspective because about one-third of adults in the United States and more than one-quarter of the world population is overweight.”
In an accompanying editorial, Jean-Pierre Després, PhD, from the Québec Heart and Lung Institute research center and the Université Laval in Canada, wrote that these findings prove that future research needs to go beyond a single BMI measurement to refine the assessment of risk for death associated with BMI category.
“Adding waist circumference to the BMI may represent a simple by key step in the introduction of a new and relevant ‘vital sign’ in clinical practice,” he wrote. – by Savannah Demko
Disclosures: Yu and colleagues report primary funding from NIH. Després reports personal fees from Torrent Pharmaceuticals Ltd.