Nutritional supplements are widely advertised with amazing health claims but few have been able to show true effects beyond placebo or control groups. In regards to strength training, two have been studied scientifically to draw conclusions on their effectiveness. Creatine has been shown to improve strength gains and muscle growth among users who are concurrently strength training. In addition, vitamin D has also been studied to determine its' effectiveness on muscle strength.
A recent systematic review in the Journal of Strength and Conditioning Research examined the evidence behind vitamin D supplementation and muscle strength (Chiang et al. 2017). 4/5 of the included trials were deemed to have excellent quality. The trials lasted from 4 to 24 weeks with dosages ranging from 600 to 5000 IU per day. Vitamin D3 showed the most positive impact on muscle strength with effects ranging from 1 to 19%. Interested patients, are encouraged to speak to their physician before beginning any supplementation.