Having a large waist circumference increases the risk of death -- even for people who are not overweight, researchers affirmed.
In a prospective study of more than 100,000 men and women over age 50, those with the biggest waistlines -- correlating with intra-abdominal obesity -- had an increased risk of dying within every category of body mass index (BMI), Eric J. Jacobs, PhD, of the American Cancer Society in Atlanta, and colleagues reported.
Even among men with a normal BMI (defined as 18.5 to <25), each increase of 10 cm (3.9 inches) in waist circumference raised their mortality risk 16% (95% CI, 1.09 to 1.23) compared with men with higher BMI categories, Jacobs' group reported in the Aug. 9/23 issue of the Archives of Internal Medicine.
For women with a normal BMI, each 10 cm/3.9 inch increase in girth increased their risk of dying by 25% (95% CI, 1.18 to 1.32) compared with heavier women, the researchers reported.
These results emphasize the importance of waist circumference as a mortality risk factor for all older adults, the investigators said.
"Regardless of weight, avoiding gains in waist circumference may reduce risk of premature mortality," they suggested in the paper.
Aside from consistent links to mortality in prior studies, a larger waist is also associated with inflammation, insulin resistance, type 2 diabetes, dyslipidemia, and coronary heart disease -- all independently of BMI.
The reason may be that a bigger waist is strongly correlated with fat deposited around the internal organs (visceral adipose tissue), "which is thought to be more pathogenic than subcutaneous adipose tissue," Jacobs and colleagues wrote in the paper.
The issue is critical, they added, because more than half of men and 70% of women age 50 to 79 in the U.S. exceed the abdominal obesity threshold -- 88 cm or around 35 inches for women and 102 cm or 40 inches for men.
Because extreme abdominal obesity is now common as well, the researchers analyzed the Cancer Prevention Study II Nutrition Cohort (CPS-II) for women whose waists measured 110 cm (43.3 inches) or more and men with girths of at least 120 cm (47.2 inches).
The study cohort of 48,500 men and 56,343 women age 50 or older was followed from 1997 through 2006.
After adjustment for BMI and other risk factors, these extreme waist circumferences more than doubled mortality risk compared with a normal waist circumference.
For men, a waist circumference of 120 cm/47.2 inches or more yielded a relative risk of 2.02 (95% 1.71 to 2.39) for mortality, compared with men who had a waist under 90 cm (35.4 inches). For women, the relative mortality risk reached 2.36 (95% CI 1.98 to 2.82) for a waist circumference of 110 cm/43.3 or greater compared with less than 75 cm (29.5 inches).
However, the association between waist circumference and mortality was linear (P<0.001), suggesting no clear threshold for risk.
Across the BMI categories, higher waist circumference appeared most strongly linked to mortality among women with normal BMI (P=0.03 for interaction with BMI category). The relative risks for a 10-cm increase in waist circumference were:
- 1.25 (95% CI 1.18 to 1.32) with normal BMI (18.5 to <25)
- 1.15 (95% CI 1.08 to 1.22) with overweight BMI (25 to <30)
- 1.13 (95% CI 1.06 to 1.20) with obese BMI of (30 or greater)
The same was not true for men, though, who had a fairly unvarying association between abdominal obesity and mortality. Each 10-cm increase in waist circumference was associated with relative risks of:
- 1.16 (95% CI 1.09 to 1.23) at a normal BMI
- 1.18 (95% CI 1.12 to 1.24) at an overweight BMI
- 1.21 (95% CI 1.13 to 1.30) at an obese BMI
The associations with waist circumference were strongest for mortality caused by respiratory disease, followed by cardiovascular disease and then cancer.
The researchers cautioned that their study was limited by self-measured and self-reported waist circumference, "undoubtedly introducing some measurement error." Limitations also included the study's observational design, which may have led to an overestimate of the findings due to confounding by factors associated with both waist circumference and mortality, they wrote.
Also, the study included only individuals age 50 and older, nearly all of whom were white, which may limit its generalizability, the researchers added.
The researchers reported having no financial conflicts of interest to disclose.
Zalman S. Agus, MD Emeritus Professor
University of Pennsylvania School of Medicine and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
Archives of Internal MedicineSource Reference: Jacobs EJ, et al "Waist circumference and all-cause mortality in a large U.S. cohort" Arch Intern Med 2010; 170: 1293-1301.