In pregnant women, a B₁₂ deficiency can substantially raise a woman's risk of giving birth to a child with a neural tube defect, such as spina bifida or anencephaly, according to a study conducted in Ireland by Molloy and colleagues. Investigators analyzed stored blood samples collected between 1983 and 1990 from 1,179 women in their early weeks of pregnancy. None had taken vitamin supplements. In 171 cases, the women had given birth to children with neural tube defects; in 107, they had a history of giving birth to a child with a neural tube defect although their current pregnancies were unaffected. The remaining 901 were control subjects whose pregnancies were unaffected.

Researchers measured the vitamin B₁₂ and folic acid (B₉) levels in the blood samples, comparing levels of the case subjects with those of the controls and using regression analysis to establish the role of B₁₂ independent of folate, which has long been known to protect against neural tube defects. Women who were extremely deficient in vitamin B₁₂, with blood levels of 149 ng/L or lower, had five times the risk of giving birth to a child with a neural tube defect, and women whose levels were deficient, with blood levels of 199 ng/L or lower, had 3.6 times the risk.

mother cares for her infant son, who has spina bifida, a birth defect involving the incomplete closure of the embryonic neural tube. A recent study found that women with extreme vitamin B

Epidemiologist James L. Mills, an author of the study and a senior investigator for the National Institute of Child Health and Human Development, said vitamin B₁₂ deficiency is more likely in "women who eat no animal products, or in those with problems that would interfere with absorption, like a recent gastrointestinal surgery or inflammatory bowel disease." Such women, said Mills, need to have their B₁₂ levels checked before considering pregnancy, since neural tube formation "is complete 28 days after conception, when many women are unaware that they're pregnant."

In older women, vitamins B₁₂ and B₉, along with B₆, may also protect against age-related macular degeneration (AMD). In a randomized, controlled trial of 5,442 female health care professionals with or at high risk for cardiovascular disease, Christen and colleagues found that daily supplementation with these vitamins reduced the relative risk of developing AMD or visually significant AMD (AMD in which best-corrected visual acuity is 20 over 30 or worse) by 34% and 41%, respectively.

Investigator Emily Y. Chew of the National Eye Institute, and a study coauthor, said that although the findings are interesting, "in this study, AMD was determined by self-report and confirmed by medical records." She suggests that future studies on the protective effects of B vitamins confirm AMD diagnoses by fundus photograph or ophthalmologic exam. "So stay tuned."

Maribeth Maher