A combined health promotion program of exercise with protein and vitamin D-enriched menu enhances skeletal muscle mass and strength in Japanese elderly men.

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• A short-term (10-day), structured exercise programme combined with a protein- and vitamin D-enriched meal plan improved muscle strength and mass in older men. However, longer-term studies are needed to confirm whether these benefits are sustained beyond this acute intervention period.

Introduction

This study aimed to assess the effectiveness of a combined health promotion programme on the prevention of frailty in older men. The programme incorporated exercise along with a menu enriched with protein and vitamin D.

Method

This was a randomised, crossover study involving seven healthy Japanese men aged 60-69 years. Participants were randomly assigned to a 10-day exercise programme with a protein- and vitamin D-enriched menu (ExN) or exercise alone (Ex), followed by a 10-day washout and crossover to the opposite programme.

Fasting blood and 24-hour urine samples were collected pre- and post-intervention (Day 1 and Day 11), alongside anthropometric measurements (bioelectrical impedance, calf circumference), muscle strength testing (timed up-and-go, grip strength), and dietary records. The study was conducted in winter to minimise sunlight-derived vitamin D synthesis as a confounder.

Results

• Physical activity: No significant between-group differences in energy expenditure or steps reported.

• Dietary intake: Ex group maintained stable dietary intake throughout the study; ExN group significantly increased intake of energy, protein (+30 g/day), fat, calcium (+527 mg/day), and vitamin D (+856 IU/day) post-intervention (p<0.05), with protein, calcium, and vitamin D intake also significantly higher than the Ex group at post-intervention (p<0.05).

• Vitamin D metabolites: Participants' baseline serum 25(OH)D3 levels (~53–57 nmol/L) fell within the adequate range (>50 nmol/L). In the ExN group, serum 25(OH)D3 rose by a modest 4.8 ± 2.8 nmol/L (p=0.003). 24,25(OH)2D3 and 3-epi-25(OH)D3 also increased significantly in ExN (p=0.046 and p=0.003, respectively).

• Urinary markers: 3-methylhistidine excretion was significantly higher in ExN than Ex post-intervention (p<0.05). Urine pH and creatinine increased significantly within the Ex group (p=0.009 and p=0.043). No other significant differences were observed.

• Muscle strength: In the ExN group, TUG time improved by 0.5 ± 0.5 s (p=0.037) and grip strength increased by 2.1 ± 2.3 kg (p=0.048); TUG was also significantly shorter in ExN than Ex post-intervention (p<0.01). Calf circumference increased modestly in the Ex group only (p=0.012).

• Body composition: In the ExN group, LBM increased by 0.6 ± 0.6 kg (p=0.045) and skeletal muscle mass by 0.3 ± 0.3 kg (p=0.025); ΔLBM was significantly greater in ExN than Ex (p<0.01). Body weight did not change significantly in either group (p=0.209). Body fat did not differ between groups.

Conclusion

A programme involving regular exercise and a nutritious meal plan, enriched with protein and vitamin D, may help reduce the risk of frailty even within a short intervention period.

• Combining resistance exercise with adequate protein and vitamin D intake may be considered when designing programmes to improve muscle mass, function and strength in older adults. However, the small cohort and short (10-day) duration make it unclear whether this reflects a genuine physiological adaptation or a transient response to an unfamiliar exercise stimulus.

• Larger-scale studies including women, alongside a broader range of frailty and activity levels, are needed to confirm these findings and improve generalisability. Longer-term follow-up (e.g., 6, 12, or 24 weeks) would help establish whether the observed benefits are sustained over time.

• Further research is needed to examine the optimal protein intake for the elderly population, as well as to determine whether an upper limit exists for this population.

• Future studies should consider other methods of assessing dietary intake to help minimise inaccuracies in the quantification of nutrient amounts.

• Further work should clarify the mechanistic basis for the protein–vitamin D combination's effect on muscle mass and strength, and test whether a similar intervention confers benefit in summer months, when higher endogenous vitamin D synthesis from sunlight may reduce the relative impact of dietary supplementation.