The reemergence in infants, and particularly in black infants, of the bone disease rickets has raised concerns about whether women at northern U.S. latitudes are getting adequate amounts of vitamin D during pregnancy. Vitamin D deficiency in utero or early in life can lead to soft bones, as well as increased risks of type 1 diabetes, asthma, and schizophrenia later in life. In addition, low levels during pregnancy may be linked to complications such as miscarriage, preeclampsia, and premature birth.

Researchers from the University of Pittsburgh and Magee-Women's Hospital evaluated 200 black and 200 white nulliparous women enrolled in the Pregnancy Exposures and Preeclampsia Prevention Study between 1997 and 2001. Blood was sampled before 22 weeks of pregnancy and just before delivery, and then a cord blood sample was taken. Although more than 90% of the women reported taking prenatal vitamins during the last trimester of pregnancy, 83% of black women and 46% of white women had inadequate levels of vitamin D at delivery. In addition, the cord blood samples showed that 92% of black infants and 66% of white infants had low vitamin D levels at birth.

Prenatal vitamins typically contain 400 IU of vitamin D. While lead author Lisa Bodnar said she feels that pregnant women should add 1,000 IU of vitamin D₃ (cholecalciferol) to their daily vitamin intake, she noted that "no studies directly evaluate this." Research is under way to determine whether taking 2,000 or 4,000 IU is safe and effective, she said.

The evidence suggests that black women may need to supplement with more vitamin D than white women do. Vitamin D is produced in the skin by sunlight, but this synthesis is reduced in people with dark skin. The latest U.S. National Health and Nutrition Examination Survey showed that in women of childbearing age, 42% of those who were black and 4% of those who were white were deficient in vitamin D. Nevertheless, said Bodnar, despite the lower levels, "We don't know from our data if black women have higher vitamin D needs per se."

Carol Potera

Figure. Colored X-ray of the legs of a child with rickets, a disease caused by insufficient calcium deposition in the bones (for which an adequate level of vitamin D is necessary). The result is weakened bone tissue and the characteristic bowing of long bones.