Age-related different relationships between ectopic adipose tissues and measures of central obesity in sedentary subjects

Abstract

Accumulation of fat at ectopic sites has been gaining attention as pivotal contributor of insulin resistance, metabolic syndrome and related cardiovascular complications. Intermuscular adipose tissue (IMAT), located between skeletal muscle bundles and beneath muscle fascia, has been linked to physical inactivity, ageing and body mass index, but little is known about its relationship with the other AT compartments, in particular with increasing age. To address this issue, erector spinae IMAT, epicardial (EAT), intraabdominal (IAAT) and abdominal subcutaneous adipose tissue (SAT) were simultaneously measured by Magnetic Resonance Imaging (MRI) and related to waist circumference measurements and age in 32 sedentary subjects without cardiovascular disease (18 men; 14 women; mean age 48.5 ± 14 years). Fasting glucose, triglycerides and HDL-cholesterol were also assessed. We observed that, after dividing individuals according to age (≤ or > 50 years), IMAT and EAT depots were significantly more expanded in older subjects (63.2 ± 8.3 years) than in the younger ones (38.4 ± 5.2 years) (p < 0.001). Overall, both IMAT and EAT showed stronger positive associations with increasing age (β = 0.63 and 0.67, respectively, p < 0.001 for both) than with waist circumference (β = 0.55 and 0.49, respectively, p < 0.01 for both) after adjusting for gender. In addition, the gender-adjusted associations of IMAT and EAT with waist circumference and IAAT were significant in individuals ≤ 50 years only (p<0.05 for all) and not in the older ones. In contrast, no age-related differences were seen in the relationships of IAAT and SAT with waist circumference. Finally, serum triglycerides levels turned out not to be independently related with ectopic IMAT and EAT. In conclusion, the expansion of IMAT and EAT in sedentary subjects is more strongly related to age than waist circumference, and a positive association of these ectopic depots with waist circumference and IAAT amount can be postulated in younger individuals only.

Figure 1. MRI measurements of adipose tissue depots.

(A) Volumetric assessment of EAT. The contours of EAT were outlined in end-diastolic images of short-axis views covering the whole left and right ventricle. (B) IMAT of the erector spinae muscles at L3–L4 disk level. IMAT is visible between muscle groups (white arrow) and beneath the muscle fascia (black arrow). Abdominal L3–L4 (C) and L4–L5 (D) MRI scans with representation of IAAT and SAT respectively (black arrows). The black arrow head indicates the fascia trasversalis dividing SAT into a deep and a superficial layer.

Figure 2. Adipose tissue depots amounts according to age.

Erector spinae IMAT area (A), EAT total volume (B), IAAT (C) and SAT (D) areas in subjects ≤50 years and >50 years. *p<0.001, **p<0.05.

Figure 3. Correlations of adipose tissue depots with waist circumference according to age.

Correlations of IMAT area (A), EAT total volume (B), SAT (C) and IAAT (D) areas with waist circumference. Solid lines represent correlations in younger subjects (≤50 years): IMAT: β = 0.46, p = 0.03; EAT: β = 0.63, p = 0.005; SAT: β = 0.81, p = 0.0001; IAAT: β = 0.51, p = 0.02 (gender-adjusted correlation coefficients). Dashed lines represent correlations in older subjects (>50 years): IMAT: β = 0.14, p = ns; EAT: β = −0.13, p = ns; IAAT: β = 0.54, p = 0.09; SAT: β = 0.76, p = 0.002.

Figure 4. Correlation of IMAT with EAT according to age.

Correlations between IMAT area with EAT total volume. Solid lines represent the correlation in younger subjects (≤50 years) (β = 0.6, p = 0.007). Dashed lines represent the non significant correlation in older subjects (>50 years) (β = −0.3, p = ns).