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Carrying extra belly fat -- that is, having an "apple" body shape -- was tied to higher mortality risk for postmenopausal women, researchers reported.

Compared with women of normal weight as defined by BMI category -- and possessing no central obesity as measured by waist circumference -- those with normal weight who did have central obesity had about 30% increased risk for all-cause mortality (HR 1.31, 95% CI 1.20-1.42), Wei Bao, MD, PhD, of the University of Iowa, and colleagues wrote in .

In addition to all-cause mortality risk, normal-weight women with central obesity also had significantly elevated risk for cancer mortality (HR 1.20, 95% CI 1.01-1.43), as well as cardiovascular mortality (HR 1.25, 95% CI 1.05-1.46).

Central obesity was also associated with increased all-cause mortality in women who were overall overweight or obese, versus normal-weight women without central obesity:

• Obesity + central obesity: HR 1.30 (95% CI 1.27-1.34)
• Overweight + central obesity: HR 1.16 (95% CI 1.13-1.20)

On the other hand, women with overweight (HR 0.91, 95% CI 0.89-0.94) or obesity (HR 0.93, 95% CI 0.89-0.94) without central obesity saw slightly reduced all-cause mortality risk, playing into the idea of the "obesity paradox."

"[W]omen with overweight based on BMI may have a greater amount of gluteofemoral adipose tissue associated with an improved metabolic and cardiovascular risk profile, which could partially explain the obesity paradox," the researchers explained.

The "findings challenge the current paradigm that measurement of abdominal fat is not recommended for individuals with normal BMI," the group wrote.

An by David Allison, PhD, of Indiana University Bloomington, and colleagues underscored how this reinforces the notion that "the scale is not everything."

"We all intuitively know that BMI, which is calculated as weight in kilograms divided by height in meters squared, is a function of total mass and not just fat mass, but we may be mistaken into thinking that those with low BMI are ipso facto fit and at low risk," they commented.

In addition, the study "highlights not only that factors such as cardiovascular fitness, lean muscle mass, or metabolic indicators (such as various hormones and metabolites) provide important additional information about risk but also that simple anatomic distribution may be predictive."

For the analysis, Bao's group drew upon the Women's Health Initiative study, including over 156,000 postmenopausal women from 40 U.S. centers between the ages of 50 and 79. These women were recruited between 1993 and 1998.

Waist circumference used to determine central obesity was measured at enrollment. Central obesity was considered a waist circumference over 88 cm. Obesity was defined by classic BMI categories: normal weight (18.5-24.9), overweight (25-29.9), or obesity (30+).

Among the entire cohort, about 2.6% of all women of normal weight possessed central obesity. These women tended to be older, nonwhite, and with less education and income. These women were also less likely to use menopausal hormones and to exercise.

Several mechanisms may underlie this elevated mortality weight in normal weight women with central obesity, the researchers explained. One may be the harmful combination of visceral fat and lack of protective muscle mass.

"Previous studies have shown that excessive visceral fat is associated with insulin resistance, hyperinsulinemia, dyslipidemia, and inflammation, which are risk factors for [cardiovascular disease] and several types of cancer, including breast cancer and colon cancer," the researchers noted.

"Future research is needed to develop and test the effectiveness of interventions to reduce risk owing to excess body fat among people with normal weight central obesity," they suggested.

Despite these interesting findings, the commentators highlighted that this study was exclusive to postmenopausal women, and therefore cannot be generalized to men or younger women.

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