Early prevention of sarcopenia could be an important strategy for muscle retention, but most studies have focused on subjects aged 65 or older. Therefore, in this study we investigated the effects of leucine-enriched protein supplementation on muscle condition in a sample including late middle-aged adults. A 12-week intervention was performed for 120 healthy community-dwelling adults by providing either leucine-enriched protein supplement [protein 20g(casein 50%+ whey 40%+ soy 10%, total leucine 3000 mg), vitamin D 800IU(20 ug), calcium 300 mg, fat 1.1 g, carbohydrate 2.5 g] or isocaloric carbohydrate supplement twice per day. Appendicular skeletal muscle mass (ASM) and lean body mass (LBM) were measured by dual-energy X-ray absorptiometry. A total of 111 participants completed the study, with a dropout rate of 9.2%. LBM normalized by body weight (LBM/Wt) was significantly increased (p < 0.001) in the intervention group (0 wk: 63.38 ± 0.85 vs. 12 wk 63.68 ± 0.83 in the intervention group; 0 wk: 63.85 ± 0.82 vs. 12 wk: 63.29 ± 0.81 in the control group). In subgroup analyses, significant differences remained only in subjects between 50 and 64 years of age. We concluded that leucine-enriched protein supplementation can have beneficial effects by preventing muscle loss, mainly for late middle-aged adults.

As the proportion of the elderly population increases rapidly, interest in musculoskeletal health is also emerging. Here, we investigated how antioxidant vitamin intake and musculoskeletal health are related. Adults aged 50 to 80 years with a body mass index (BMI) of 18.5 to 27.0 kg/m 2 were included. Bone mineral density (BMD), lean mass (LM), appendicular skeletal muscle mass index (ASMI) were measured using dual-energy X-ray absorptiometry (DXA), and the grip strength and knee extension using hand dynamometer. Nutrient intakes were measured using a 24-hour recall questionnaire. A total of 153 adults (44 men and 109 women) participated in this study. A partial correlation analysis showed a significant positive relationship between vitamin E and BMD and between vitamin C and LM/Height. Participants were classified into three groups according to whether their vitamin E and C intake met the recommended intake for Dietary Reference Intakes for Koreans (KDRIs). The prevalence of having low T-score (< −1.0) and low ASMI (< 7.0 for men and < 5.4 for women) was 51.3% and 15.4% in the group with vitamins C and E intakes below KDRIs. After adjusting for sex, smoking status and energy, protein, vitamin D, and calcium intake, the group with vitamins C and E both below the KDRIs displayed a significantly lower BMD at all test sites and LM/Height compared with vitamin C and/or E intake above the KDRIs groups. We conclude that sufficient intake of vitamin E and C is important for maintaining BMD and lean mass in Korean adults over 50 years of age.

Early prevention of sarcopenia can be an important strategy for muscle maintenance, but most studies target subjects at slightly pre-sarcopenic state. Our previous paper describes the effect of protein supplements rich in leucine and vitamin D on muscle condition, and in this paper, we performed a sub-analysis to evaluate who benefitted the most in terms of improvement in muscle health. A 12-week randomized clinical trial of 120 healthy adults (aged 50 to 80) assigned to an intervention group (n = 60) or control group (n = 60) were analyzed. Subjects in the intervention group received, twice per day, a protein supplement containing (per serving) 800 IU of vitamin D, 20 g of protein (3 g of total leucine), 300 mg of calcium, 1.1 g of fat, and 2.5 g of carbohydrate. The subjects were classified into ‘insufficient’ and ‘sufficient’ groups at 25-hydroxyvitamin D (25[OH]D) value of 30 ng/mL. The skeletal muscle mass index normalized to the square of the skeletal muscle mass (SMM) height (kg/m 2 ) increased significantly in the ‘insufficient group’ difference value of change between weeks 0 and 12 (Δ1.07 ± 2.20; p = 0.037). The SMM normalized by body weight (kg/kg, %) was higher, but not significantly, in the insufficient group (Δ0.38 ± 0.69; p = 0.050). For people with insufficient (serum 25[OH]D), supplemental intake of protein and vitamin D, calcium, and leucine and adequate energy intake increases muscle mass in middle-aged and older adults and would be likely to exert a beneficial effect on muscle health. Trial Registration Clinical Research Information Service Identifier: KCT0005111