In a prospective study, men and women whose thighs measured under 60 cm (23.6 inches) in circumference had a significantly increased risk for both heart disease and death, Berit L. Heitmann, MD, 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 metabolism.
But some researchers are not convinced about the potential mechanism. Douglas P. Zipes, MD, 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, despite a similar observation in COPD patients."
"I would have predicted fat thighs to be a cardiovascular risk because of a relationship to obesity," Zipes said. "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."
So the researchers conducted a prospective cohort 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 55 cm.
"Above this threshold," they said, "there did not seem to be any further benefit of having larger thighs."
In regression models that controlled for body fat, height, BMI, and waist circumference, smaller thigh circumference was independently related to total death, cardiovascular disease, and coronary heart disease for men.
It was also linked to total death for women in these models. But associations with cardiovascular disease and coronary heart disease became weaker as more confounders were added, the researchers said -- although that may be attributable to small study size and a lack of statistical power.
Thresholds of thigh circumference existed for all endpoints:
- 62 cm for men and women for total mortality
- 56 cm for cardiovascular disease and coronary heart disease for men
- 68 cm for cardiovascular disease in women
- 60 cm for coronary heart disease for women
Above these thresholds, the protective effect of having larger thighs was no longer related to thigh size, whereas below the threshold the risk was greatly increased, the researchers said.
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.
Also, lack of subcutaneous fat might negatively impact glucose and lipid metabolism.
The researchers concluded that thigh circumference "might be a relevant anthropometric measure to help general practitioners in early identification of individuals at an increased risk of premature morbidity and mortality."
However, the study was limited by its lack of statistical power and because it did not measure tissue composition of the thighs, so researchers could not test hypotheses about muscle mass.
In an accompanying editorial, Ian A. Scott, MD, of Princess Alexandra Hospital in Brisbane, said it would "seem logical that having bigger thighs would be a reflection of greater adiposity, and that this would increase the risk of heart disease. However, the authors cite studies suggesting that too little muscle or subcutaneous fat in the lower limbs may predispose to adverse glucose and lipid metabolism."
Scott 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."
He added that "randomized trials are needed to test whether interventions that increase thigh muscle mass through increased physical activity ... decrease cardiovascular risk more than current practice."
The study was supported by the Danish Medical Research Council.
Neither the researchers nor the editorialists reported any conflicts of interest.
- Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, RN, BC-ADM, CDE, Nurse Planner
British Medical JournalSource Reference: Heitmann BL, et al "Thigh circumference and risk of heart disease and premature death: Prospective cohort study" BMJ 2009; DOI: 10.1136/bmj.b3292.
British Medical JournalSource Reference: Scott IA "Thigh circumference and risk of heart disease and premature death" BMJ 2009; DOI: 10.1136/bmj.b3292.