Should You Take Folate or B12 to Conceive?

If you could become pregnant, take folic acid — but take it for the baby, not to conceive faster. It prevents a serious birth defect in a pregnancy you go on to have. It has not been shown to help you get pregnant.

If you are the male partner and you bought it to improve a semen result, the honest answer is that it has been tested and it did not work. Two large randomised trials, one of 2,370 couples and one of 1,171 men, found no improvement in semen quality and no more pregnancies.

Vitamin B12 is the weaker half of the question. It has never been tested on its own for fertility outcomes at all.

The Folic Acid and Zinc Supplementation Trial (FAZST) enrolled 2,370 couples at four American fertility centres between 2013 and 2017. The male partner took either folic acid with elemental zinc, or an identical placebo, every day for six months. It was designed to settle exactly the question you are holding a bottle about.

Nothing improved. Sperm concentration, motility, morphology, volume and total motile count were all not significantly different at six months. Live birth was not different either. Two things did change, and both went the wrong way: sperm DNA fragmentation was higher on the supplement, and stomach upset was more common — abdominal discomfort or pain in 66 men (6%) on the supplement versus 40 (3%) on placebo, with nausea and vomiting also more frequent.

The trial carries a published correction (JAMA 2020;323(12):1194). Two rows were transposed in the baseline characteristics table. The results above are unaffected.

The trial authors' own conclusion: these findings "do not support the use of folic acid and zinc supplementation by male partners in the treatment of infertility".

This is the closest anyone has come to testing it. The SUMMER trial, published in 2025, randomised 1,171 men across 21 Dutch hospitals and fertility clinics to a daily supplement or an identical placebo for six months. The supplement contained folic acid and vitamin B12 together with zinc, betaine, cystine, niacin, vitamin B6 and vitamin B2 — much the same mixture sold as a men's fertility multivitamin.

Ongoing pregnancy within six months was 33.8% on the supplement versus 37.5% on placebo, a difference that was not statistically significant. In the four-to-six-month window the investigators call the window of optimal treatment effect, because that is when a full cycle of sperm production would have been exposed to the supplement, the supplement group did worse: ongoing pregnancy 15.5% versus 21.5%. No secondary outcome, including semen parameters and DNA fragmentation, differed between the groups.

Two limits matter when you read that. It tested a combination, so nothing in it can be pinned on B12 specifically. And a single significant result inside a subgroup window is not proof that a supplement causes harm — the main result is simply that it did not help.

As for B12 alone: a PubMed search on 30 September 2026 found no randomised trial testing vitamin B12 by itself against semen quality or live birth. Not a negative trial — no trial. Anything you read asserting that B12 raises sperm count is not resting on one.

None of the above touches the one folate claim that is settled. A Cochrane review of five randomised trials covering 6,708 births found that daily folic acid before and around conception reduced neural tube defects — spina bifida and anencephaly — with a risk ratio of 0.31 (95% CI 0.17 to 0.58). Cochrane rated that high-quality evidence, its top grade. Among women who had already had an affected pregnancy, the reduction in recurrence was similar, risk ratio 0.34 (95% CI 0.18 to 0.64) across 4 randomised trials and 1,846 births.

NICE's maternal and child nutrition guideline (NG247, 2025) puts the timing plainly in recommendation 1.1.3: folic acid should be started before trying for a baby, ideally three months before, or as early as possible after a positive test, and continued for at least the first 12 weeks of pregnancy. It also says to keep taking the supplement even where flour and other food is fortified.

Read the outcome that review measured, because it is the whole distinction on this page. It counted birth defects in babies who were conceived. It did not count how many women conceived. The same review found no clear effect on cleft lip, cleft palate, congenital heart defects, or miscarriage.

Do not stop a prescription because of a web page, including this one. Ask which of three different reasons it was given for, because the evidence above only speaks to one of them.

• To prevent neural tube defects, for someone who could become pregnant. Keep taking it. This is the use the Cochrane evidence supports and NG247 recommends.
• To correct a measured deficiency — a low folate or low B12 blood result, pernicious anaemia, coeliac disease, or after bariatric surgery. That is treatment for the deficiency, and it has its own reasons that have nothing to do with the trials on this page.
• To improve a semen result. This is the use FAZST and SUMMER tested and did not support, and the use NICE NG257 recommendation 1.24.6 [2026] advises against: "Do not offer supplements, antioxidants or medical treatments to improve sperm DNA integrity (fragmentation)."

If it is the third reason, a fair question to your doctor is what result is expected to change and when it will be checked. A supplement with no review date is hard to stop.

One abnormal semen analysis is not a diagnosis. NICE NG257 recommendation 1.17.3 says to offer a repeat confirmatory test when the first result is abnormal, and 1.17.4 sets the interval: "Undertake repeat confirmatory tests ideally 3 months after the initial analysis to allow time for the cycle of spermatozoa formation to be completed."

Three months is not arbitrary. When researchers labelled sperm DNA directly with a stable isotope in 11 men with normal sperm concentrations, labelled sperm first appeared in the ejaculate after 64 days on average, give or take 8, ranging from 42 to 76 days. Anything you change today shows up in a result taken about three months later, whether that is a supplement, an illness, a fever or stopping smoking.

Two more things worth knowing before you spend money. NG257 1.17.6 says not to carry out testing for sperm DNA integrity (fragmentation) at all — so a fragmentation test sold alongside a supplement is measuring something the guideline does not ask for. And if the real question is whether you are actually deficient, the answer comes from measuring folate or B12 in blood, not from taking a supplement and hoping.

Related: whether foods or supplements actually improve sperm quality, zinc and sperm health, and what the male fertility supplement evidence adds up to.

Several things on this page are genuinely unsettled, and a few common claims are weaker than they look.

• That antioxidant supplements improve live birth in men. The 2022 Cochrane review of 90 studies found an odds ratio of 1.43 (95% CI 1.07 to 1.91) for live birth across 12 randomised trials and 1,283 men — but rated it very low certainty, and when the trials at high risk of bias were removed the signal disappeared: Peto odds ratio 1.22 (95% CI 0.85 to 1.75) across 8 randomised trials and 827 men. The benefit rests on the weakest studies.
• That vitamin B12 does anything for fertility. There is no randomised trial of B12 alone with a fertility outcome to cite, in either direction.
• That folic acid is useless for every man. FAZST tested one dose pairing, for six months, in couples already seeking fertility treatment. It does not tell you what happens in a man with a documented folate deficiency, which no trial has addressed separately.
• That the higher DNA fragmentation in FAZST harmed anyone. The difference was small, live birth did not fall, and NG257 1.17.6 does not recommend measuring fragmentation in the first place.
• That folic acid prevents miscarriage. The Cochrane review looked: risk ratio 1.10 (95% CI 0.94 to 1.28) across 5 trials and 7,391 pregnancies, moderate-quality evidence. No effect either way.
• That any of this is a substitute for finding the cause. Sometimes the answer is testing, timing, or a simpler treatment than IVF — and sometimes IVF is not indicated at all.

It is worth saying the obvious thing about why supplements are so hard to put down. When you are waiting, a bottle is often the only part of this that feels like it is in your hands. That is a real feeling, and it is not a reason the evidence changes.