Skeletal muscle index an important predictor of breast density

Skeletal muscle index (SMI) appears to be a significant correlate of breast density, a recent South Korea study has found.

Researchers conducted a cross-sectional analysis of 143,456 women who had undergone comprehensive examinations from 2012 to 2016. Breast density was measured using mammography, and SMI was assessed using bioelectrical impedance analysis.

Majority of participants (80.2 percent) were postmenopausal, while the remaining 19.8 percent were premenopausal. Women in the latter category were more likely to have dense breasts, which in turn was positively associated with SMI, height, and oestradiol levels, and negatively correlated with age, weight, body mass index (BMI), and vitamin D levels.

After categorizing the participants into quartiles of SMI, multivariate logistic regression analysis found that the likelihood of dense breasts was increased by more than two times in the highest (>40.1) vs lowest (<35.5) quartiles in both premenopausal (odds ratio [OR], 2.65, 95 percent confidence interval [CI], 2.52–2.79) and postmenopausal (OR, 2.39, 95 percent CI, 2.02–2.82; p<0.001 for both) women.

Similarly, each unit increase in SMI significantly raised the likelihood of higher mammographic density in both premenopausal (OR, 1.15, 95 percent CI,1.15–1.16) and postmenopausal women (OR, 1.13, 95 percent CI, 1.11–1.15; p<0.001 for both).

Subsequent analysis using the relative weights (RW) statistical package revealed that of all the factors assessed, SMI had the highest relative importance for predicting breast density (RW, 23.62). Other important predictors were age (RW, 22.74), menopausal state (RW, 15.02), and waist circumference (RW, 16.55).

“These results suggest that SMI is a measure to overcome the inconsistency in BMI observed in previous mammographic density-related studies; this could be explained by the strong relationship between skeletal muscularity and breast parenchymal tissue,” the researchers said.