Age-Related Changes in Intramyocellular Lipid in Humans by in vivo 1H-MR Spectroscopy

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Abstract
It is considered that the increasing intramyocellular lipid (IMCL) affects health risks and muscle attenuation. Though body fat increases significantly with age in lean humans, it is not known whether IMCL increases or not. In this study, we investigated the changes with age in IMCL concentrations in skeletal muscles using (1)H-MR spectroscopy and studied them in relation to body fat percentage, waist-hip ratio, and blood components. Twenty-four lean young (age 21.2 +/- 1.9, BMI 21.5 +/- 1.8) and 23 lean old (age 70.9 +/- 2.4, BMI 21.7 +/- 1.3) subjects took part in the study. Subjects were grouped by gender into age- and BMI-matched young and old groups. The (1)H-MRS was obtained from the tibialis anterior (TA), medial gastrocnemius (MG) and soleus (SOL) muscles. The IMCL content in SOL and MG in the old was found to be higher (p < 0.01) than that in the young. No age difference in IMCL content in TA was found. IMCL concentrations in SOL were higher than those in MG and TA in the order of SOL > MG > TA (p < 0.01). IMCL content correlated significantly with waist-hip ratio in all skeletal muscles. A significant relationship was observed between percent body fat and IMCL in TA and MG (p < 0.05). However, no correlation was found between IMCL content in each muscle and BMI. The IMCL content in all skeletal muscles significantly correlated with HbA1c, triglyceride, total cholesterol and LDL cholesterol concentrations. These results suggest that increased IMCL in both lean older men and women might be related to body composition, blood lipids and lipoprotein profiles, and that this might affect muscle attenuation.