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Greater Adipose Tissue Infiltration in Skeletal Muscle among Older Men of African Ancestry

Department of Epidemiology (I.M., J.A.C., E.S., Y.S., C.H.B., L.H.K., K.A.F., J.M.Z.), Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania 15260; University of Minnesota (I.M., J.A.C., E.S., Y.S., C.H.B., L.H.K., K.A.F., J.M.Z.), VA Medical Center, Minneapolis, Minnesota 55417; Department of Radiology (M.A.P., K.E.E.), McMaster University, Hamilton, Ontario, Canada L8N 3Z5; Division of Endocrinology and Metabolism (C.L.G.), University of Pittsburgh’s Department of Medicine, Pittsburgh, Pennsylvania 15261; and Tobago Health Studies Office (B.H.G., A.L.P., V.W.W.), Scarborough, Tobago, Trinidad and Tobago

Address all correspondence and requests for reprints to: Iva Miljkovic, M.D., Ph.D., Department of Epidemiology, Center for Aging and Population Health, University of Pittsburgh, 130 North Bellefield Avenue, Room 542, Pittsburgh, Pennsylvania 15213. E-mail: miljkovici{at}edc.pitt.edu.

Context: There is substantial variability across ethnic groups in the predisposition to obesity and associated metabolic abnormalities. Skeletal muscle fat has been identified as an important depot that increases with aging and may contribute to the development of diabetes.

Objective: We tested whether men of African ancestry have greater calf intermuscular adipose tissue (IMAT), compared to Caucasian men, and whether IMAT is associated with type 2 diabetes (T2D).

Design: We measured fasting serum glucose, body mass index, total body fat by dual-energy x-ray absorptiometry, and calf skeletal muscle composition by quantitative computed tomography in 1105 Caucasian and 518 Afro-Caribbean men aged 65+.

Results: Compared to Caucasian men, we found greater IMAT and lower sc adipose tissue in Afro-Caribbean men at all levels of total adiposity (P < 0.0001), including the subset of men matched on age and dual-energy x-ray absorptiometry total body fat percentage (P < 0.001). In addition, IMAT was 29 and 23% greater, whereas sc adipose tissue was 6 and 8% lower among Caucasian and Afro-Caribbean men with T2D, respectively, compared to men without T2D (P < 0.01). Observed differences in intermuscular and sc fat, both ethnic and between men with and without T2D, were independent of age, height, calf skeletal muscle and total adipose tissue, and lifestyle factors.

Conclusions: Our analyses suggest that despite lower total adiposity, skeletal muscle fat infiltration is greater among African than among Caucasian ancestry men and is associated with T2D in both ethnic groups. Additional studies are needed to determine the mechanisms contributing to ethnic differences in skeletal muscle adiposity and to define the metabolic and health implications of this fat depot.