It sounds counterintuitive given the health risks of obesity, but up to a point, bigger thighs might mean a smaller risk of heart disease or premature death, researchers say.
In a study relesased Thursday, men and women whose thighs measured less than about 24 inches in circumference were found to have an increased risk for both heart disease and death, Dr. Berit Heitmann of Copenhagen University Hospital and colleagues reported online in the British Medical Journal.
"Smaller thighs are a disadvantage to health and survival for both sexes," the researchers said.
Physicians currently use several measures used to predict cardiovascular risk, including waist-to-hip ratio and body mass index (BMI). However, none is notably superior, so the researchers investigated another potential predictor -- thigh size.
The explanation: lower muscle mass in the lower body and in the legs has been linked to the development of type 2 diabetes. Some studies have reported that insulin resistance may be provoked in the leg muscle, and that low levels of subcutaneous fat in the thighs leads to adverse glucose and lipid, or fat, metabolism.
But some researchers are not convinced about this potential mechanism. Dr. Douglas Zipes, past president of the American College of Cardiology, said that "waist circumference and its possible relationship to metabolic syndrome and diabetes made sense as a risk factor. This does not.
"I would have predicted fat thighs to be a cardiovascular risk because of a relationship to obesity," Zipes added. "Further, some people are just big, and will have thick thighs, and others small. So I would be interested in the thigh sizes of some young -- and tiny -- women who are at low risk of cardiovascular disease."
He said further studies must replicate the results "before I become a believer and start measuring the thighs of my patients."
The researchers conducted a prospective study of 1,436 mean and 1,380 women participating in the Danish MONICA study (Monitoring Trends in and Determinants of Cardiovascular Disease).
Participants were followed for 10 years for cardiovascular and coronary heart disease, and for 12.5 years to track total deaths.
Over 10 years, 263 men and 140 women developed cardiovascular disease and 103 men and 34 women had coronary heart disease. After 12.5 years, 257 men and 155 women died.
The researchers found that small thigh circumference was associated with an increased risk of cardiovascular and coronary heart disease and total mortality in both men and women, especially as thigh circumference dropped below about 22 inches.
"Above this threshold," they said, "there did not seem to be any further benefit of having larger thighs."
Even controlling for other variables such as body fat, height, BMI, and waist circumference, smaller thigh circumference was independently related to total death, cardiovascular disease, and coronary heart disease for men.
The findings are in line with earlier observations of a threshold effect for a low total fat-free mass, they said, meaning risk might depend on too little muscle mass, rather than too little fat or small pelvic size.
However, the study was limited by the fact that it did not measure tissue composition of the thighs, so researchers could not test hypotheses about muscle mass.
In an accompanying editorial, Dr. Ian Scott of Princess Alexandra Hospital in Brisbane called for more research "to see whether measuring thigh circumference with a tape measure adds anything more to our clinical management than eliciting risk factors from the history, examining the cardiovascular system, and measuring serum lipids."