The Women’s Health Initiative (WHI) study has caused controversy regarding how being overweight relates to health risks.  It followed more than 90,000 women for 7 years resulting in researchers reporting that obesity, but not overweight, was linked to increased risk of death from all causes.

Some people have taken these findings a step further to suggest that there may even be a health advantage to being overweight.  How can this be?  Examining the data more closely can help explain what appears to be a paradox.

It has been well known for years that being slightly overweight may provide a small health advantage among older women, ages 70 to 80+.  The WHI study included approximately 22,000 women aged 70 or older.  It is expected that this group would have the highest mortality; therefore, when all ages are included in the analysis, researchers found that being overweight (indicated by having a BMI of 25-29.9) showed no increase in mortality rates.

Yet when you examine each age group, overweight women in the 50-59 and 60-69 age groups both showed increased mortality rates compared to women in the healthy weight range (indicated by having a BMI <25). The lower mortality in the overweight (BMI of 25-29.9) group was only found in the women over 70. However, all age groups showed increased mortality rates in the obese group (indicated by having a (BMI of 30+).

In fact, researchers found that obese women (BMI of 30+) were twice as likely to die from coronary heart disease as women in the healthy weight range (BMI <25). Obesity increased the risk of diabetes by 4 to 10 times and more than doubled the risk for hypertension. Overall, obesity increased the risk of death from any cause by 30-60% in the moderately obese women, and increased mortality rates by 2-3 times in the very obese (BMI of 35-40+).

It should be noted that most of the excess mortality due to obesity resulted from increased high blood pressure, high blood lipids, and diabetes among the obese women.

The Bottom Line:

Being overweight moderately increases health risks for women younger than 70; however, the primary increase in mortality is found among women in the obese range, especially those with a BMI of 35-40 or higher.

Source: McTigue, et al. (July 2006). Mortality and Cardiac and Vascular Outcomes in Extremely Obese Women. Journal of the American Medical Association, 296:79-86.