Low birth-weight infants: the continuing ethnic disparity and the interaction of biology and environment.

African-American infants weigh on average 200-300 grams less at birth than do European-American infants, leading to a two-fold higher rate of low birth-weight (LBW) infants. This birth weight disparity has not changed significantly over the past 95 years. Numerous research studies have been undertaken to elucidate this disparity. While various factors have been found to be associated with increased risk for having a LBW infant, including maternal anthropometrics, health and age, prenatal care, and socioeconomic status, none have been found to entirely and adequately explain the continued birth-weight differential. Researchers have concluded that there is something different in the environment and/or genetics of African-American women compared to European-American women, but are at a loss to clearly define the factor other than to say it must relate to the racism suffered by African-American women leading to more stress during pregnancy. While racism is probably an additional factor, one genetic/environmental variable, which has been overlooked, is the interaction of heavy pigmentation with degree of latitude. Heavy pigmentation blocks ultraviolet B (UVB) radiation. At high latitudes, such as in the US region, inadequate exposure to UVB radiation prevents the conversion of the prohormone to the hormonal form of vitamin D. The resulting low levels of serum vitamin D in the pregnant woman disrupt calcium homeostasis leading to intrauterine growth retardation, premature labor, and hypertension: all risk factors for LBW infants.