BCAAs & Vitamin D: Boost Muscle & Mobility?

Clinical Evidence

The randomized controlled trial investigated whether a combined intervention of a high‑protein food supplement containing branched‑chain amino acids (BCAAs) and vitamin D, together with a structured exercise program, could improve soft lean mass (SLM) and physical function in older adults with reduced functional capacity. Participants were community‑dwelling elderly (mean age ≈ 78 years; 55 % female) who exhibited decreased gait speed or grip strength at baseline. Over a 12‑week period, the intervention group (n ≈ 80) received the BCAA‑vitamin D‑enriched high‑protein food (providing 6 g BCAAs and 800 IU vitamin D per serving) twice daily, alongside thrice‑weekly supervised resistance and balance training. The control group (n ≈ 80) performed the same exercise regimen but received an isocaloric placebo without BCAAs or vitamin D.

The primary outcome, change in SLM measured by dual‑energy X‑ray absorptiometry (DXA), showed a mean increase of 0.9 kg in the supplement group versus 0.2 kg in controls (between‑group difference = 0.7 kg; 95 % CI 0.3–1.1 kg; p = 0.001). Secondary functional outcomes included the Short Physical Performance Battery (SPPB) and hand‑grip strength. The SPPB score improved by 1.4 points in the intervention group versus 0.5 points in controls (difference = 0.9 points; 95 % CI 0.4–1.4; p = 0.002). Hand‑grip strength increased by 2.3 kg versus 0.8 kg (difference = 1.5 kg; 95 % CI 0.5–2.5; p = 0.004). No significant differences were observed in body weight or fat mass. Adherence to supplement intake was >90 % in both groups, and no serious adverse events were reported.

Mechanisms of Action

BCAAs (leucine, isoleucine, valine) stimulate muscle protein synthesis (MPS) primarily via activation of the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, enhancing translation initiation in skeletal muscle. In older adults, anabolic resistance attenuates MPS responses to protein; the high leucine content (≈ 3 g per dose) is intended to overcome this resistance. Vitamin D may augment muscle function through genomic regulation of calcium‑handling proteins and non‑genomic activation of phosphatidyl‑inositol‑3‑kinase (PI3K)/Akt pathways, potentially synergizing with BCAA‑driven mTORC1 activation. The combined nutritional and exercise stimulus is hypothesized to augment net protein balance, leading to modest gains in SLM and functional performance.

Safety Profile

The trial reported no serious adverse events attributable to the supplement. Mild gastrointestinal discomfort (e.g., bloating) was reported by 5 % of participants in the supplement group, comparable to the control group (4 %). No significant changes in serum creatinine, liver enzymes, or calcium levels were observed, suggesting no renal or hepatic toxicity at the administered dose. Participants with severe renal impairment (eGFR < 30 mL/min/1.73 m²) were excluded, limiting generalizability to this population. No drug‑interaction assessments were reported; however, BCAA supplementation may theoretically interfere with medications affecting amino‑acid metabolism (e.g., levodopa) and high vitamin D doses may interact with thiazide diuretics or hypercalcemia‑prone conditions.

Dosage Information

The intervention provided 6 g of BCAAs (approximately 2 g each of leucine, isoleucine, and valine) and 800 IU of vitamin D3 per serving, administered twice daily (total 12 g BCAAs and 1,600 IU vitamin D per day) mixed into a high‑protein food matrix (≈ 30 g protein per serving). The supplementation period lasted 12 weeks, concurrent with supervised resistance and balance training three times per week.

Evidence Quality Assessment

This investigation is a single, double‑blind, placebo‑controlled RCT with a moderate sample size (≈ 160 participants) and a well‑defined elderly cohort. The study demonstrates statistically significant improvements in SLM and functional outcomes, supporting a causal relationship between the BCAA‑vitamin D supplement plus exercise and modest functional gains. However, the single‑study nature, limited duration (12 weeks), and exclusion of participants with renal disease constrain the generalizability. The lack of long‑term follow‑up and limited reporting on biochemical markers further limit the robustness. Overall, the evidence provides moderate-quality support for the efficacy of BCAA‑vitamin D supplementation combined with exercise in improving lean mass and physical function in older adults, but additional larger, longer‑term trials are needed to confirm durability and safety across broader populations.