Intermuscular adipose tissue rivals visceral adipose tissue in independent associations with cardiovascular risk

Abstract

Background: The metabolic implications of intermuscular adipose tissue (IMAT) are poorly understood compared to those of visceral adipose tissue (VAT) even though the absolute quantities of both depots are similar in many individuals.

Objective: The aim was to determine the independent relationship between whole-body IMAT and cardiovascular risk factor parameters.

Design: Whole body magnetic resonance imaging (MRI) was used to quantify total skeletal muscle (SM), total adipose tissue (TAT) of which IMAT, defined as the AT visible by MRI within the boundary of the muscle fascia, is a sub-component. Fasting serum measures (n=262) of glucose, total cholesterol (T-Chol), high-density lipoprotein cholesterol (HDL-Chol), triglycerides (TG), protein bound glucose (PBG, n=206) and insulin (n=119) were acquired in healthy African-American (AA, n=78) and Caucasian (Ca, n=109) women (body mass index (BMI) 26.5+/-5.7 kg/m(2); 44.4+/-16.4 years) and men (39 AA, 62 Ca; BMI 25.6+/-3.5 kg/m(2); 45.6+/-17.4 years). General linear models identified the independent effects of IMAT after covarying for SM, VAT, TAT, race, sex and two-way interactions.

Results: Significant independent associations were observed for IMAT with glucose (P<0.001), PBG (P<0.001) and T-Chol (P<0.05). The association of IMAT with cholesterol differed by race in such a manner that for a unit increase in IMAT, T-Chol increased more rapidly in Ca compared to AA (P<0.05). TG, HDL-Chol and insulin had no independent association with IMAT.

Conclusion: The strong independent associations of IMAT with fasting glucose and PBG suggest that IMAT may be related to glucose metabolism; however, IMAT is also associated with T-Chol in Ca.

Figure 1

Residual of PBG after adjustment for SM, VAT, TAT, race and sex according to the regression equation: PBG = 0.93 − 0.001(SM) + 0.01(VAT) − 0.002(TAT) + 0.04(AA) − 0.002(male), (s.e.e. = 0.09mg/g) as a function of IMAT (kg).

Figure 2

Residual of total cholesterol after adjustment for SM, VAT, TAT and sex according to the regression equation: T-Chol = 177.75 − 1.04(SM) + 2.98(VAT) − 0.49(TAT) + 13.52(male), (s.e.e. = 38.20 mg/dl) as a function of IMAT (kg) in Ca (●) and AA (△). Solid and dashed lines represent Ca and AA, respectively.