For decades, advice about preventing birth defects before pregnancy has focused overwhelmingly on women. Take folic acid. Get enough key nutrients. Avoid alcohol. But new research suggests the nutritional health of the father before conception may deserve more attention too.
In a large 2026 study, researchers found that lower levels of vitamin B12 and folate in both mothers and fathers around conception were associated with a higher prevalence of birth defects. The paternal findings are particularly interesting because fathers have historically received far less attention in research on preconception nutrition. Of the two nutrients, B12 showed the stronger association in fathers, but folate was part of the picture too.
Published in the Annals of Internal Medicine, the research followed thousands of parents through the Shanghai Preconception Cohort, measuring nutritional markers close to conception. That’s important because most previous research into vitamins and birth defects has concentrated on mothers rather than examining the nutritional status of both parents during this critical window.
The study doesn’t prove that low B12 or folate in fathers causes birth defects, nor does it mean men planning a family should start taking high-dose supplements. But it raises an intriguing possibility: a father’s nutritional status in the months before conception may matter more to a baby’s development than researchers once assumed.
What the Shanghai Cohort found
Researchers analyzed blood samples from 17,765 women during the first four months of pregnancy, along with a smaller group of 3,032 couples whose nutritional markers were measured within four months of conception. Across the study, researchers identified more than 400 confirmed birth defects.
Vitamin B12 produced some of the most striking results. Among the couples measured close to conception, fathers with B12 levels below 148 pmol/L had a predicted prevalence of 55.5 birth defects per 1,000 births. For mothers at similarly low B12 levels, the figure was 49.6 per 1,000. The predicted prevalence fell by more than half at B12 concentrations above 295 pmol/L.
Folate showed a relationship as well. Fathers with red blood cell folate concentrations below 453 nmol/L had a predicted birth defect prevalence of 26.4 cases per 1,000 births. For mothers in the same low-folate range, the figure was 28.3 per 1,000. The researchers found B12 had the stronger association, but the results suggest paternal folate status may also deserve further investigation.
The findings also weren’t limited to neural tube defects, the birth defects most famously associated with folate. More than half of the roughly 400 defects identified in the study affected the heart, leading researchers to suggest that B12 and folate could be relevant to a broader range of major structural birth defects.
Why paternal nutritional deficiencies could biologically matter
Sperm has traditionally been thought of as little more than a genetic delivery vehicle, but more recent science has complicated that picture. Fathers contribute not only DNA to an embryo but also epigenetic information that can influence how genes function.
Folate and vitamin B12 are both involved in one-carbon metabolism, a network of biological processes important for DNA synthesis and methylation. That has given researchers a plausible reason to investigate whether deficiencies in these nutrients could affect sperm before conception.
An editorial accompanying the new study pointed to animal research in which insufficient paternal folate altered the sperm epigenome and was associated with increased birth defects in offspring. That doesn’t establish that the same process occurs in humans, but it provides biological context for why researchers are now looking more closely at paternal nutrition.
Sperm cells are vulnerable to environmental and nutritional cues during spermatogenesis and epididymal maturation. Spermatogenesis, the process by which the testes continuously produce new sperm cells, takes approximately 64 to 74 days in humans, which is one reason nutritional status in the months before conception may be particularly relevant.
The Shanghai study itself does not establish a mechanism. It observed associations between parental B12 and folate levels and birth defect rates. Why those associations exist, and how much the father’s nutritional status directly contributes, remain open questions.
The folate picture is especially important
Folate and vitamin B12 work closely together in the body, but the evidence surrounding folate and pregnancy has a much longer history.
Maternal folate deficiency is one of the most consistently identified risk factors for neural tube defects, a category that includes spina bifida. The neural tube develops extremely early, typically before many people know they are pregnant.
According to the CDC, spina bifida affects about 1,300 babies a year in the United States, occurring in approximately 1 in 2,875 births. Folic acid supplementation has been a sustained public health priority, and mandatory folic acid fortification of enriched grains has contributed to a measurable decline in neural tube defects.
The American College of Obstetricians and Gynecologists recommends that most women of reproductive age take a daily supplement containing at least 400 mcg of folic acid. That guidance applies regardless of whether pregnancy is planned because the neural tube closes before most people realize they have conceived.
What makes the new study interesting is that it moves the folate conversation beyond mothers. The paternal association doesn’t establish that fathers should follow the same supplementation recommendations, but it adds evidence to the broader idea that folate status before conception may matter on both sides of a pregnancy.
What vitamin B12 is and where it comes from
Vitamin B12, also called cobalamin, is involved in DNA synthesis and the production of red blood cells. The recommended dietary allowance for adults is 2.4 micrograms per day.
Vitamin B12 is naturally found primarily in animal-derived foods such as meat, fish, eggs, and dairy. People who eat little or no animal products, including strict vegetarians and vegans, can be at greater risk of inadequate intake. Certain medications, including proton pump inhibitors and metformin, can also interfere with B12 absorption over time.
For anyone curious about their own B12 status, common symptoms of B12 deficiency can range from fatigue and tingling in the hands or feet to more gradual neurological changes, though deficiency can also be present without obvious symptoms, particularly in the early stages.
A 2026 systematic review published in Frontiers in Neuroscience concluded that adequate maternal B12 status is consistently associated with better language, memory, and cognitive performance in children, suggesting the nutrient’s importance may extend beyond structural birth defects into long-term neurodevelopment. Whether paternal B12 similarly influences cognitive outcomes in offspring has not yet been studied in sufficient depth to draw conclusions.
The study’s real limits
The Shanghai findings are observational. Parents were not randomly assigned to different B12 or folate levels, which means the research cannot prove that deficiencies in either nutrient caused higher rates of birth defects. Other variables, including overall diet quality, socioeconomic factors, genetics, and environmental exposures, could contribute to the associations.
The study also involved a Chinese population. How well the findings generalize to populations with different diets, environmental exposures, genetic backgrounds, or baseline rates of nutrient deficiency remains an open question.
Perhaps most importantly, the findings don’t establish a new supplementation recommendation for prospective fathers. While the evidence supporting maternal folic acid supplementation is extensive, paternal B12 and folate supplementation for preventing birth defects hasn’t been established by clinical trials.
The researchers themselves acknowledged that unmeasured genetic and biological factors could have contributed to the results. The study therefore gives researchers a strong reason to investigate paternal nutrition further, rather than providing proof that changing a father’s B12 or folate intake will prevent birth defects.
Read More: Signs of vitamin B12 deficiency you should never ignore
What this means for both parents
For generations, preconception nutrition has focused primarily on the person who will carry the pregnancy, and for good reason. Evidence supporting maternal folic acid and other nutritional recommendations is extensive, while research into paternal nutrition remains comparatively young.
That isn’t changing because of a single study. What is changing is the assumption that the father’s health before conception has little biological relevance.
The Shanghai research is particularly interesting because it examined nutritional markers in both parents close to conception. Both B12 and folate were associated with birth defect prevalence, with B12 showing the stronger paternal relationship. That gives researchers a clearer reason to investigate whether correcting deficiencies in prospective fathers could eventually become part of preconception care.
For now, the practical advice remains much more established on the maternal side. The American College of Obstetricians and Gynecologists recommends that people who can become pregnant consume at least 400 mcg of folic acid daily, ideally beginning before conception, because neural tube development occurs extremely early in pregnancy. Nothing in this study establishes a comparable supplementation recommendation for prospective fathers.
Instead, the bigger takeaway is about where the science is heading. Pregnancy may begin in one person’s body, but the months leading up to conception involve the biology of both parents. Understanding how much a father’s nutrition contributes to a child’s development is a question researchers are only beginning to answer.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.
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