Vitamin D supplementation reduced risk of acute respiratory tract infection (adjusted OR 0.88, 95% CI 0.81–0.96); greatest benefit in those with baseline deficiency (<25 nmol/L) and those receiving daily or weekly dosing rather than bolus doses.

Vitamin D at 700–800 IU/day reduced hip fracture risk by 26% (RR 0.74) and any nonvertebral fracture by 23% (RR 0.77); no significant benefit was observed at 400 IU/day.

Vitamin D insufficiency is prevalent among athletes, particularly indoor athletes and those in northern latitudes in winter. Insufficiency is associated with reduced muscle strength, power, and endurance; supplementation of 2,000–6,000 IU/day recommended to maintain 25(OH)D >40 ng/mL.

Magnesium citrate produced the greatest mean serum Mg concentration following both acute and chronic 300 mg/day supplementation, demonstrating superior bioavailability over magnesium oxide and amino-acid chelate preparations.

Magnesium supplementation (median 368 mg/day for 3 months) reduced systolic BP by 2.00 mmHg (95% CI 0.43–3.58) and diastolic BP by 1.78 mmHg (95% CI 0.73–2.82) vs placebo; 300 mg/day for ≥1 month sufficient to raise serum Mg and lower BP.

Strong evidence that 3–6 mg/kg caffeine improves endurance, strength, and power; benefits consistent but moderated by genetics and habituation.

Caffeine prolongs sleep latency, reduces total sleep time and efficiency; clinically meaningful disruption occurs with 400 mg within 8–12 h of bedtime.

Caffeine significantly improves reaction time (g=0.28) and accuracy (g=0.27) on attention tasks; dose ≥200 mg shows larger effects.

Consistent improvements in strength, power, and training volume; safe for long-term use (up to 30 g/day for 5 years studied). Loading optional; maintenance commonly 3–5 g/day.

Oral creatine may improve short-term memory and intelligence/reasoning in healthy individuals; effect on other cognitive domains unclear.