Influence of Vitamin D Supplementation and Exercise Therapy on Musculoskeletal Strength

Musculoskeletal health plays a pivotal role in maintaining functional independence, quality of life, and overall metabolic health across the lifespan. Muscle weakness and reduced physical performance are increasingly recognized as major contributors to disability, falls, fractures, and morbidity, particularly among middle-aged and elderly populations¹. Among the modifiable factors influencing musculoskeletal function, vitamin D status and physical activity have gained substantial scientific attention².

Vitamin D is a fat-soluble secosteroid hormone that exerts its biological effects through vitamin D receptors (VDRs), which are widely expressed in skeletal muscle cells³. Activation of VDRs regulates calcium homeostasis, protein synthesis, mitochondrial function, and muscle fiber differentiation⁴. Vitamin D deficiency has been associated with proximal muscle weakness, reduced muscle mass, impaired balance, and increased risk of falls⁵. Epidemiological studies indicate that hypovitaminosis D affects nearly one billion individuals worldwide, with higher prevalence in South Asian populations due to limited sun exposure, skin pigmentation, and dietary inadequacy⁶.

Exercise therapy, particularly resistance and weight-bearing training, is a well-established intervention for improving muscle strength, endurance, and neuromuscular coordination⁷. Regular physical activity stimulates muscle hypertrophy, enhances motor unit recruitment, and improves bone mineral density⁸. Despite the independent benefits of vitamin D and exercise, emerging evidence suggests a synergistic interaction between the two interventions⁹.

Experimental studies indicate that adequate vitamin D levels may enhance muscle responsiveness to exercise by improving muscle protein synthesis, calcium handling, and neuromuscular efficiency¹⁰. Conversely, exercise may upregulate VDR expression in skeletal muscle, thereby potentiating the biological actions of vitamin D¹¹. However, clinical studies evaluating the combined effects of vitamin D supplementation and structured exercise therapy on musculoskeletal strength have yielded inconsistent results¹².

Given the high prevalence of vitamin D deficiency and physical inactivity in developing countries, understanding the combined impact of these interventions has significant clinical and public health implications¹³. The present study was therefore designed to evaluate the influence of vitamin D supplementation and exercise therapy, individually and in combination, on musculoskeletal strength and functional performance in vitamin D–deficient adults.

This prospective, randomized interventional study was conducted in the Department of Physical Medicine and Rehabilitation at a tertiary care teaching hospital over a period of 12 months.

Study Population

Adults aged 30–65 years attending outpatient clinics were screened for serum 25-hydroxyvitamin D levels. Eligible participants were enrolled after obtaining written informed consent.

Inclusion Criteria

·       Age between 30 and 65 years

·       Serum 25-hydroxyvitamin D level <20 ng/mL

·       Sedentary or moderately active lifestyle

·       Ability to perform basic physical exercises

·       Willingness to comply with study protocol

Exclusion Criteria

·       History of metabolic bone disease or neuromuscular disorders

·       Chronic kidney disease, liver disease, or malabsorption syndromes

·       Use of vitamin D or calcium supplements within the last 6 months

·       Long-term corticosteroid or anticonvulsant therapy

·       Recent fractures or major orthopedic surgery

·       Pregnancy or lactation

Intervention Groups

Participants were randomized into three groups (n=40 each):

·       Group A: Vitamin D supplementation (cholecalciferol 60,000 IU weekly for 8 weeks, followed by monthly maintenance)

·       Group B: Exercise therapy (supervised resistance and balance training, 45 minutes/session, 5 days/week)

·       Group C: Combined vitamin D supplementation and exercise therapy

Outcome Measures

Musculoskeletal strength and function were assessed at baseline and after 12 weeks using:

·       Handgrip strength (dynamometer)

·       Lower limb strength (chair stand test)

·       Balance (Timed Up and Go test)

·       Physical performance (Short Physical Performance Battery)

Statistical Analysis

Data were analyzed using SPSS software. Continuous variables were expressed as mean ± SD. Paired and unpaired t-tests and ANOVA were used, with p <0.05 considered statistically significant.

Table 1. Baseline Demographic Characteristics

Baseline characteristics were comparable across groups.

Table 2. Serum Vitamin D Levels (ng/mL)

Significant improvement occurred in vitamin D–supplemented groups.

Table 3. Handgrip Strength (kg)

Greatest improvement was observed in the combined group.

Table 4. Lower Limb Strength (Chair Stand Test, seconds)

Table 5. Balance Performance (TUG Test, seconds)

Table 6. Physical Performance Score

The present study demonstrates that combined vitamin D supplementation and structured exercise therapy produces superior improvements in musculoskeletal strength and functional performance compared to either intervention alone. These findings highlight the synergistic interaction between nutritional and physical interventions in optimizing muscle health.

Vitamin D supplementation alone resulted in modest but significant improvements in muscle strength and balance. This observation is consistent with previous studies demonstrating that correction of vitamin D deficiency improves proximal muscle strength and reduces fall risk¹⁴,¹⁵. The presence of VDRs in skeletal muscle fibers supports the biological plausibility of these effects¹⁶.

Exercise therapy alone produced greater improvements than vitamin D supplementation alone, particularly in lower limb strength and physical performance. Resistance and balance training are known to enhance neuromuscular coordination, muscle hypertrophy, and motor unit recruitment¹⁷. Similar findings have been reported in randomized trials evaluating exercise interventions in middle-aged and elderly populations¹⁸.

Notably, the combined intervention group exhibited the greatest improvements across all outcome measures. This synergistic effect may be attributed to

improved muscle calcium handling, enhanced

protein synthesis, and increased VDR expression induced by exercise¹⁹,²⁰. Recent meta-analyses have also suggested that vitamin D supplementation enhances the adaptive response to resistance training in deficient individuals²¹.

Our findings align with studies by Bischoff-Ferrari et al. and Antoniak et al., which reported improved muscle performance when vitamin D supplementation was combined with physical training²²,²³. However, some trials have reported neutral effects, possibly due to differences in baseline vitamin D status, dosage, or exercise intensity²⁴.

The study underscores the importance of addressing both nutritional deficiencies and physical inactivity in clinical practice. Integrating vitamin D screening and structured exercise programs may represent a cost-effective strategy to improve musculoskeletal health and prevent disability.

Combined vitamin D supplementation and exercise therapy significantly improves musculoskeletal strength, balance, and functional performance in vitamin D–deficient adults. This integrated approach should be considered in preventive and rehabilitative strategies aimed at reducing musculoskeletal morbidity.

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