Intramuscular Fat and Associations With Metabolic Risk Factors in the Framingham Heart Study

OBJECTIVE: Intramuscular fat accumulates between muscle fibers or within muscle cells. We investigated the association of intramuscular fat with other ectopic fat deposits and metabolic risk factors. APPROACH AND RESULTS: Participants (n=2945; 50.2% women; mean age 50.8 years) from the Framingham Heart Study underwent multidetector computed tomography scanning of the abdomen. Regions of interest were placed on the left and right paraspinous muscle, and the muscle attenuation (MA) in Hounsfield units was averaged. We examined the association between MA and metabolic risk factors in multivariable models, and additionally adjusted for body mass index (BMI) and visceral adipose tissue (VAT) in separate models. MA was associated with dysglycemia, dyslipidemia, and hypertension in both sexes. In women, per standard deviation decrease in MA, there was a 1.34 (95% confidence interval, 1.10-1.64) increase in the odds of diabetes mellitus, a 1.40 (95% confidence interval, 1.22-1.61) increase in the odds of high triglycerides, and a 1.29 (95% confidence interval, 1.12-1.48) increase in the odds of hypertension. However, none of these associations persisted after adjustment for BMI or VAT. In men, we observed similar patterns for most risk factors. The exception was metabolic syndrome, which retained association in women even after adjustment for BMI and VAT, and low high density lipoprotein and high triglycerides in men, whose associations also persisted after adjustment for BMI and VAT. CONCLUSIONS: MA was associated with metabolic risk factors, but most of these associations were lost after adjustment for BMI or VAT. However, a unique association remained for metabolic syndrome in women and lipids in men.