Vitamin D, 25-OH

In men who are deficient (<30 ng/mL), correcting vitamin D modestly raises testosterone — usually by 50–100 ng/dL. In men who are already replete, additional vitamin D has no T-raising effect.

25-OH vitamin D, or 25-hydroxyvitamin D, is the storage form of vitamin D that circulates in your blood, and it's the standard test for assessing your vitamin D status. It's used because it has a long half-life and reflects your combined intake from sun, food, and supplements over the preceding weeks. When a lab reports "vitamin D," this 25-OH test is almost always what they mean.

They're two different forms. 25-hydroxyvitamin D (25-OH) is the storage form and the correct test for checking whether you have enough vitamin D. 1,25-dihydroxyvitamin D is the active hormone the body makes from it, tightly regulated by the kidneys, and its level can stay normal or even rise while you're actually deficient — so it's the wrong test for gauging vitamin D status and is reserved for specific problems like certain kidney or calcium disorders. If you want to know your vitamin D level, order the 25-OH test.

Reference ranges aren't sex-specific — the same targets apply to men and women. Below 20 ng/mL is generally considered deficient, 20–30 ng/mL insufficient, and roughly 30–80 ng/mL sufficient, with many clinicians favoring 40–60 ng/mL as optimal. The units are ng/mL in the US; some labs report nmol/L, where you'd multiply by about 2.5.

It depends on which threshold you use, and there's genuine debate. Some bodies consider 20 ng/mL adequate for the general population, while the Endocrine Society and many clinicians prefer 30 ng/mL or higher for sufficiency. A value of 25 ng/mL therefore falls in a gray zone — above the deficiency line but below the more conservative sufficiency target — and many practitioners would suggest supplementing to get comfortably above 30.

If you're on TRT and your 25-OH vitamin D is below about 40 ng/mL, a common approach is 2,000–5,000 IU daily, often paired with vitamin K2 for cardiovascular protection. Retest after a couple of months to confirm you've reached your target rather than dosing blindly, and confirm the plan with your physician.