Vitamin D and Sperm: Deficiency Is Common, Benefit Is Not Proven

On the evidence available now, no. The largest randomised trial of vitamin D in infertile men - 330 men with serum 25(OH)D at or below 50 nmol/L, treated for 150 days - found no change in sperm concentration, motility or morphology against placebo (Blomberg Jensen, Journal of Clinical Endocrinology & Metabolism, 2018). A 2026 systematic review pooling 11 studies, 8 of them randomised, in 1,168 infertile men, found small gains in progressive motility and testosterone but no significant effect on clinical pregnancy or live birth.

That is not the same as saying vitamin D does not matter. Deficiency is widespread in India, and correcting it has well-established value for bone and muscle health. What has not been shown is that correcting it makes a man more fertile. Those two sentences are both true at once, and most pages on this topic only print the first one.

This is the trial worth knowing about, because it measured what patients care about rather than a lab number. Blomberg Jensen and colleagues screened 1,427 infertile men and randomised 330 with 25(OH)D at or below 50 nmol/L to cholecalciferol plus calcium or placebo for 150 days. Blood levels rose as intended in the treated group, which confirms the supplement was absorbed and working biochemically.

The primary outcome - semen quality - did not move. Spontaneous pregnancy was higher in the treated group at 7.3% versus 2.4%, but the confidence interval crossed zero (-0.6% to 10.5%), so that result is compatible with no effect. One subgroup did show something: among oligozoospermic men, live birth was 35.6% versus 18.3% on placebo. The trial's own authors wrote that this finding "may be of clinical importance and warrant verification by others".

A subgroup result from a trial whose primary outcome was negative is a hypothesis, not a treatment. It is the single most promising signal in this literature, and eight years on it has not been replicated in a trial designed to test it.

Because the trials did not support it. NICE guideline NG257, recommendation 1.24.6 [2026], reads: "Do not offer supplements, antioxidants or medical treatments to improve sperm DNA integrity (fragmentation)." The same section also says not to offer androgens to treat semen abnormalities (1.24.3), which is worth knowing if a clinic has framed vitamin D as a testosterone strategy.

The cautionary precedent is the Folic Acid and Zinc Supplementation Trial, published in JAMA in 2020. It randomised 2,370 couples, and the two ingredients most commonly sold in male fertility supplements produced no difference in live birth - 34% versus 35% on placebo - and a small but statistically significant increase in sperm DNA fragmentation, 29.7% versus 27.2%. Supplements are not automatically neutral, and a micronutrient that looks protective in a laboratory can measure worse in people.

Very common, and no. A meta-analysis of 65 South Asian studies covering 44,717 participants put pooled deficiency in India at 67% (95% CI 61 to 73), with a weighted mean level of 19.15 ng/mL across the region. Deficiency was more prevalent in females than males. Living at a sunny latitude does not protect a population from this.

High prevalence is a reason to take deficiency seriously as a general health problem. It is not evidence that supplementation improves fertility - the trials tested exactly that and came back negative on semen parameters. A common deficiency and an effective treatment for infertility are two different claims, and the slide from the first to the second is the most frequent error on this subject.

Pooled deficiency was higher in females than males across the region, and the trial evidence on the female side is negative too - a 630-woman randomised trial of vitamin D before IVF found no improvement in clinical pregnancy. That is covered separately in vitamin D and fertility in women, because the outcomes measured there are different ones: ovarian reserve, IVF success and pregnancy loss rather than semen parameters.

The test itself is cheap, widely available in India and measures serum 25-hydroxyvitamin D. What it will not do is explain subfertility or predict whether treatment will work. Deciding whether to check it is reasonably framed as a general health question rather than a fertility one.

A low result would change three things, none of them a fertility intervention:

• It identifies a deficiency that has established consequences for bone and muscle health, which a prescriber can treat on that basis.
• It gives a baseline, so a repeat level later shows whether whatever was prescribed is actually being absorbed - the Danish trial confirmed levels rose, which is why its negative semen result is informative rather than ambiguous.
• It rules the question out, so attention moves to the things that do change outcomes: a properly performed semen analysis, the female partner's assessment, and the timing of treatment.

Thresholds are not agreed, which is itself useful to know. The Fertility and Sterility analysis used below 20 ng/mL as deficient; the Danish trial enrolled men at or below 50 nmol/L, which is the same cut-off in different units. Different labs and guidelines draw the line in different places, and no threshold has been validated against fertility outcomes.

Not on the basis of this page. Stopping a prescription is a conversation with whoever wrote it, and there are good reasons to be on vitamin D that have nothing to do with sperm. If the prescription was made for a documented deficiency, bone health or a musculoskeletal complaint, the trials described here say nothing against it.

What is worth asking is what the prescription is for. If the answer is "to improve your sperm" or "to reduce DNA fragmentation", that is the specific claim NICE NG257 1.24.6 advises against, and the specific claim the randomised evidence did not support. If the answer is "your level was low", that is a different and defensible reason. Dosing is a prescriber's decision and this page deliberately does not give one - the trial regimens quoted here were research protocols, not advice.

Written out plainly, because the gap between what is measured and what is claimed is wide on this topic:

• That vitamin D supplementation improves sperm concentration, motility or morphology in a way that changes whether a couple conceives. The randomised trials measured this and did not find it.
• That vitamin D protects sperm DNA. NICE NG257 1.24.6 [2026] advises against offering supplements or antioxidants for this purpose, and the folic acid and zinc trial measured fragmentation moving in the wrong direction.
• That the oligozoospermia subgroup result is real. It has not been replicated in a trial designed to test it, and the original authors called for verification.
• That vitamin D raises testosterone enough to matter for sperm production. The 2026 review found a small rise in serum testosterone alongside no change in clinical pregnancy or live birth, so the hormone number moved and the outcome did not.
• That a man's vitamin D level explains a miscarriage. One analysis of 154 men reported higher pregnancy loss below 20 ng/mL, adjusted odds ratio 9.0, but the 95% confidence interval ran from 1.3 to 61.3 - too wide to act on, from a secondary outcome in a single study.
• That there is a vitamin D threshold below which a man should be treated for fertility reasons. No cut-off has been validated against fertility outcomes.

If you have been taking vitamin D for a year in the belief that it was quietly helping, it is reasonable to feel let down reading this. The more useful reading is that it frees up the question - the thing that changes outcomes is usually a diagnosis, not a supplement.