Waisting Away: Waist Circumference and Mortality
Abstract & Commentary
By Russell H. Greenfield, MD, Editor
Synopsis: Results of this impressive observational trial suggest that waist circumference may be a more telling sign of mortality risk than BMI, especially among those whose BMI measures do not place them in the category of obesity.
Source: Jacobs EJ, et al: Waist circumference and all-cause mortality in a large U.S. cohort. Arch Intern Med 2010;170:1293-1301.
Body mass index (BMI) is being determined for most patients when they go to their doctor's office these days, but waist circumference (WC) often is not. The authors of this observational study sought to determine the association between WC and mortality within categories of BMI, and to examine the effects of a very large WC on mortality. They reviewed data from the Cancer Prevention Study II Nutrition Cohort (initial enrollment from 1992-93; n = 184,190), a large prospective study of primarily older adults.
Subjects completed a mailed questionnaire on enrollment that included demographic data, medical factors, and behavioral factors. A follow-up was completed in 1997 that included additional health-related data such as current weight and smoking status. At the same time, subjects were provided with tape measures and asked to measure and record their WC, instructions having been provided on the proper technique. BMI was calculated based on height measurements obtained from a later follow-up date (1982) and the weight measures from 1997. A total of 48,500 men and 56,343 women, mainly white, were included in the analysis. Subjects who had lost more than 10 pounds or gained more than 25 pounds from 1992-1997 were excluded from the final analysis, the former to reduce bias from disease-related weight loss. Participants younger than age 50 years in 1997 were also excluded.
WC was characterized using 5 cm increments, and a wide variety of variables, including hormone therapy in women and smoking status, were adjusted for in determination of hazard ratios.
At trial's end the data showed that subjects in the highest WC category were more likely than their smaller-waist counterparts to be less-educated, have a higher BMI, be physically inactive, be former smokers, and have a history of significant medical illness. No associations were found between any of the other variables studied, including hormone therapy and WC. Before adjustments for BMI, WC was associated with statistically significant increases in mortality only at levels of 110 cm or more in men and 95 cm or more in women. After adjustments for BMI, all levels of WC higher than the lowest level were associated with higher mortality, with RR estimates increasing approximately linearly. Among those with the highest WC's whose measurements placed them in the obese category there was an even higher risk of mortality (RR = 1.17 in men [95% CI, 1.10-1.23]; RR = 1.23 in women [95% CI, 1.14-1.32]). In both men and women, WC was positively associated with higher mortality rates across all BMI categories. Of note, higher WC levels in women were more strongly associated with mortality among those in the normal BMI category (18.5 to < 25) than among those who were overweight or obese. In men, the association between WC and mortality did not vary significantly by BMI. Within categories of BMI mortality rates increased with increasing levels of WC, but the obverse was not true within categories of WC mortality rates did not increase with increasing levels of BMI. The RRs associated with a 10-cm increase in WC ranged from approximately 15%-25% within the various BMI categories, with the strongest association observed among women in the normal BMI category. The overall association between WC and mortality was strongest for respiratory disease, followed by cardiovascular disease and cancer. The authors concluded that avoiding gains in WC may reduce risk of premature mortality regardless of body weight.
Commentary
Meaning no disrespect, but the "800-pound gorilla" in the room is the issue of overweight and obesity. Research strongly suggests that where fat accumulates in a person as they gain weight may be similarly important to the amount of added fat.
A large WC is representative of increased visceral adiposity. This is important because the abdominal fat depot appears to be very active, secreting inflammatory factors that promote insulin resistance, diabetes, and heart disease. Thus, it should not be surprising to see how mortality rates increase in tandem with growing WC measures. Results of a series of prior studies support this conclusion, but the findings of the current study suggest that larger WCs may have important adverse health consequences even among people with a BMI < 30.
According to WC guidelines a measurement > 102 cm (40 inches) in men and > 88 cm (35 inches) in women signifies obesity. The authors note that 50% of men and 70% of women in the United States between the ages of 50-79 years now exceed the WC threshold for abdominal obesity. One of the weaknesses of this trial, however, is the fact that subjects self-determined their WC. Although the authors acknowledge this concern, they note that self-determination of WC generally has been accepted. It is still a methodological weakness; however, the study's strengths (not the least of which is sample size) dwarf the few design flaws present.
BMI is considered by many to be the standard by which overweight and obesity is categorized, even though the limitations of the index are now well understood and accepted. This study points out that we may not be attending to a more obvious measure of risk, that being WC. As the obesity epidemic only seems to worsen despite individual and even international efforts to stem the tide, calls for systemic changes in at least access to healthy food and physical activity are growing louder. Public health officials and practitioners continue to strive to identify easy means for people to understand the dangers of becoming overweight, and spreading the message of WC may be another effective method. Perhaps we should be asking people to get a sense of how their clothes feel and measure their WCs even more than asking them to step on the scale. Certainly, we should be making WC part of the standard set of measurements determined at any office visit (a good reference on the proper technique and interpretation of waist circumference can be found at http://www.health.gov.au/internet/abhi/publishing.nsf/Content/factsheet-waist-measurement.
Results of this impressive observational trial suggest that waist circumference may be a more telling sign of mortality risk than BMI, especially among those whose BMI measures do not place them in the category of obesity.You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
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