BODYDATA
Supplements

Vitamin D

Evidence ratingModerate

A fat-soluble vitamin synthesized in the skin from sunlight. Involved in bone metabolism, immune function, and muscle function. Deficiency is common in indoor lifestyles and low-sunlight environments. Athletes show high deficiency rates, and associations with muscle strength, immunity, and bone density are well-researched.

An ingredient with growing research

Buy

(PR)
View on AmazonView on iHerb

The links below include affiliate links (PR).

Effects reported in research

Improved muscle strength and power in deficient individuals (confirmed with supplementation)

Maintained bone density and reduced fracture risk (effective combined with calcium)

Support for immune function (associated with lower infection risk)

Support for testosterone production (association suggested when correcting deficiency)

Dosage & timing

  • 1,000–4,000 IU (25–100 μg)/day.
  • Take with dietary fat for improved absorption.
  • Supplementation is particularly effective when serum 25(OH)D is below 30 ng/mL.

Cautions

  • •Fat-soluble, so excess accumulation is possible.
  • •Long-term intake above 10,000 IU/day may cause hypercalcemia.
  • •Periodic blood level monitoring is recommended.

Supporting research

Meta-analysis

Effects of vitamin D supplementation on muscle strength in athletes: A systematic review

Journal of Science and Medicine in Sport, 2015

A systematic review of vitamin D supplementation and muscle strength in athletes and physically active adults. Supplementation may improve strength in deficient athletes, but results were inconsistent across studies and depended on baseline deficiency status. With few included trials and high heterogeneity, additional benefit is likely limited when vitamin D is already sufficient.

View study details

Last checked: 2026-06-23