Should I take vitamin D?
For your health if you are short of it, not for your lifting: topping up a deficiency is sensible, but it does not add strength or muscle.
Vitamin D matters for bone health and immune function, and in northern countries most people run low in winter because the sun sits too low to make any. That is a health reason to supplement, and the usual advice is 10 to 25 micrograms (400 to 1,000 IU) a day in the dark months, or whatever your doctor advises after a blood test.
What it is not is a performance supplement. Even in people who started deficient, correcting it did not add strength or muscle beyond the training itself.
Compare
Sources
2
- Zhang, L. et al. (2019). Effect of vitamin D supplementation on upper and lower limb muscle strength and muscle power in athletes: a meta-analysis. PLoS One 14(4). 8 trials, 284 athletes: no effect on overall strength or jump power, with a small signal for lower limb strength only.
- Savolainen, L. et al. (2024). Vitamin D supplementation does not enhance gains in muscle strength and lean body mass or influence cardiorespiratory fitness in vitamin D-insufficient middle-aged men engaged in resistance training. Nutrients 16(19). 12 weeks of lifting with 8,000 IU a day in men who started insufficient: the same strength and lean mass gains as placebo.