Introduction: Intracellular fat within muscle and visceral tissue has been suggested to adversely influence bone development.
Design: We aimed to compare associations between intramuscular and subcutaneous fat and cortical bone outcomes in young adults, in cross-sectional analyses based on the Avon Longitudinal Study of Parents and Children.
Method: Data were collected from a research clinic conducted at 17 years of age. Intramuscular fat (IMF; inverse of muscle density) and subcutaneous fat area (SFA) were estimated using Stratec XCT2000L pQCT, as were periosteal circumference (PC), cortical bone mineral density (BMDC) and cortical thickness (CT). Multivariable linear regression was used to assess the relationship between IMF/SFA and cortical bone outcomes. Interactions were examined with candidate metabolic pathways, i.e. insulin, C-reactive protein (CRP) and β-C-telopeptides of type I collagen (CTX), as measured on fasting blood samples.
Results: In analyses based on 3946 individuals (boys=1703), IMF was positively associated with PC (β=0.07; 95%CI 0.04, 0.1), BMDC (β=0.21; 0.17, 0.26) and CT (β=0.37; 0.33, 0.42) (adjusted for age, height, gender and muscle cross-sectional area). SFA was positively associated with PC (β=0.10; 0.07, 0.12), but no association was seen with BMDC (β=−0.01; −0.05, 0.02) or CT (β=0.01; −0.02, 0.04). In subsequent analyses (n=2085, boys=941) adjustments for insulin, CRP and CTX were made to assess candidate intermediary metabolic pathways. Similar associations were observed after adjustment for insulin and CRP, but adjusting for CTX attenuated the association between IMF and BMDC by 30% (β=0.14; 0.20, 0.08).
Conclusion: Although IMF and SFA were positively associated with cortical bone mass, the nature of these relationships differed in that IMF was predominantly associated with CT and BMDC, whereas SFA was mainly associated with PC. Other than a contribution of bone resorption to associations between IMF and BMDC, these relationships were independent of candidate metabolic pathways.
18 May 2013 - 22 May 2013