A large Chinese study expands preconception nutrition beyond the mother, but it does not prove that supplements prevent abnormalities.
SHANGHAI, CHINA
Higher vitamin B12 levels in both parents around conception were associated with a lower prevalence of congenital abnormalities, according to a prospective cohort study published in the Annals of Internal Medicine. The findings suggest that paternal nutrition may deserve greater attention alongside maternal health when couples prepare for pregnancy.
Researchers recruited participants from 29 sites across Greater Shanghai and analysed more than 30,000 completed pregnancies. The principal analyses included 3,032 couples whose blood was tested within four months before conception and 17,765 women tested before the fourth month of pregnancy. Investigators measured vitamin B12 and red-blood-cell folate, or vitamin B9, and recorded confirmed defects among live births, stillbirths and pregnancies terminated because of fetal abnormalities.
Among women tested before conception, the estimated prevalence of birth defects declined from 49.6 to 16.2 cases per 1,000 pregnancies between the lowest and highest B12 concentrations. The paternal pattern was similar but smaller, falling from 55.5 to 24 cases per 1,000. For fathers, the apparent benefit levelled off after concentrations became moderately high, meaning the results do not support the assumption that continually increasing B12 produces progressively greater protection.
Higher maternal folate levels during early pregnancy were also associated with fewer abnormalities. That finding is consistent with the established importance of folic acid in preventing neural-tube defects. Vitamin B12 contributes to DNA production, red-blood-cell formation and neurological function, and is naturally present in meat, fish, poultry, eggs and dairy products, as well as some fortified foods.
The study remains observational. It identifies an association but cannot demonstrate that low B12 caused the defects or that supplementation would have prevented them. Diet, socioeconomic conditions, health status, genetics and access to prenatal care may have influenced both vitamin levels and pregnancy outcomes. The predominantly Han Chinese population and the absence of mandatory folic-acid fortification in the study setting also limit how confidently the results can be applied internationally.
The findings therefore support better nutritional assessment before conception, including consideration of both parents, rather than indiscriminate supplementation. People following vegan diets or living with conditions that impair B12 absorption may face greater deficiency risks, but testing and treatment should be discussed with a qualified clinician. Established folic-acid recommendations remain essential and should not be replaced by unproven assumptions about B12.
Hechos que no se doblan. / Facts that do not bend.