Vitamin D3

What is vitamin D3?

Vitamin D is a fat-soluble vitamin that the skin makes when exposed to sunlight and that also comes from a few foods, such as fatty fish, fish liver oils, egg yolks and fortified milk and cereals. Vitamin D3 (cholecalciferol) is the form made in skin and the form most often used in supplements. The body converts it into active hormones that help absorb calcium and maintain bones, and that act on muscles, immune cells and many other tissues.

The NIH Office of Dietary Supplements (ODS) lists Recommended Dietary Allowances of 15 to 20 mcg (600 to 800 IU) per day for adults, depending on age, and a tolerable upper intake level of 100 mcg (4,000 IU) per day for adults (ODS vitamin D fact sheet).

What the research says

Vitamin D’s role in bone health and in preventing deficiency diseases such as osteomalacia is well established. Many older adults, people with darker skin, people who spend little time outdoors and people with obesity have lower vitamin D levels and may benefit from supplementation, ideally guided by a blood test.

The evidence for vitamin D and the prostate is mixed. The research cited by ODS includes observational studies and meta-analyses that reached different conclusions about circulating vitamin D and prostate cancer risk, including some that found a higher risk with higher vitamin D levels (ODS). We found no good clinical trials showing that vitamin D supplements improve urinary flow, prostate size or prostate symptoms in men. Among studies of so-called testosterone boosters, vitamin D (cholecalciferol) was the most studied ingredient, but most trials did not show a rise in total testosterone (Morgado et al., 2024).

In short, vitamin D is worth getting in adequate amounts for general health, not as a prostate remedy.

How it’s used in supplements

Vitamin D3 is found in multivitamins, calcium products and stand-alone capsules, commonly at 25 to 125 mcg (1,000 to 5,000 IU). A 50 mcg (2,000 IU) dose sits above the RDA but below the upper limit. People who already take a vitamin D supplement or multivitamin should add up the total so they stay below 100 mcg per day unless their doctor advises otherwise.

Vitamin D toxicity almost always comes from excessive supplement use and can cause high blood calcium. ODS notes that vitamin D can interact with orlistat, statins, steroids and thiazide diuretics (ODS). People with kidney disease, sarcoidosis or a history of high calcium or kidney stones should talk with a doctor before supplementing.