Vitamin B12 — found in poultry, meat, fish and dairy products — helps the body produce and maintain healthy nerve cells. It is also used to make red blood cells and DNA. A new study from Fudan University in China found that its levels in both men and women before conception are associated with a lower risk of birth defects. Authors of the study argue that these findings highlight the importance of both paternal and maternal nutrition before conception and during early pregnancy. For mothers, the risk of birth defects decreased steadily as their vitamin B12 levels increased. For fathers, the risk dropped as B12 levels increased initially but then levelled off once they reached moderately high vitamin levels.Such findings demonstrate what previous studies overlooked: the father’s vitamin B12 deficiencies around the time of conception may also impact the risk for birth defects, researchers said. The study, published in the journal Annals of Internal Medicine, included over 3,000 couples who provided blood samples within 4 months before conception, alongside 17,765 women tested at four months’ gestation or earlier.  The researchers measured vitamin B12 and B9 (folate) levels and examined their relationship with birth defects in live births, stillbirths and pregnancies ending because of foetal abnormalities.  They found that predicted prevalence of birth defects fell from 49.6 to 16.2 cases per 1,000 pregnancies between mothers with the highest and lowest B12 levels, with a similar but smaller effect for fathers. Mothers with adequate red blood cell levels of vitamin B9 in early pregnancy also showed a lower predicted prevalence of birth defects. Earlier research has also identified benefits later in life for children whose mothers had adequate B12 levels during pregnancy.A separate 2026 systematic review of 22 studies concluded that adequate maternal B12 status is consistently associated with better language, memory and cognitive performance in children.