Human breast milk itself is not inherently deficient in the hormone known as Vitamin D. However, a lactating mother who has low levels of the hormone, through a combination of inadequate sun exposure and low dietary intake, may produce breast milk with low levels of Vitamin D.
Risk Factors for Vitamin D Deficiency in Breastfed Babies
- Baby gets little exposure to sunlight. People who spend little time outdoors, use high-SPF sunscreen, or live in northern latitudes with limited sunlight may have lower levels of Vitamin D.
- Mother and baby have dark skin pigmentation. People with darker skin have more natural protection from solar radiation and, thus, may require more exposure to sunlight for adequate Vitamin D synthesis.
- Mother has a low level of Vitamin D, especially during pregnancy. The baby's initial store of Vitamin D is provided by the mother's body during gestation.
- Mother and baby are exposed to lead, which inhibits Vitamin D synthesis (The FDA released a study that found lead in most supplements for women and children [J. Agric. Food Chem. 2008, 56, 6892-6896].)
Sunlight for Vitamin D Synthesis
According to Cynthia Good Mojab, MS, IBCLC, RLC, Vitamin D is not actually a vitamin, but a steroid hormone produced in the body after direct exposure of the skin to ultraviolet B (UVB) radiation in sunlight [LEAVEN, Vol. 39 No. 4, August-September 2003, pp. 75-79].
Ms. Mojab identifies exposure to sunlight as the biologically normal means for humans of all ages to obtain sufficient Vitamin D, and therefore does not consider human milk to be deficient. She posits that when there are no underlying organic causes, such as premature birth or liver or kidney disease, "Vitamin D deficiency" is actually a case of sunlight deficiency.
Food Sources of Vitamin D
Vitamin D occurs naturally in only a few foods, including liver, egg yolk, and fatty fish (salmon, mackerel, sardines, herring, and cod liver oil). Because only a few foods outside of fortified foods contain significant levels of Vitamin D, it is unusual for people to obtain adequate levels of the hormone through dietary sources alone.
Although human milk typically contains less Vitamin D than fortified infant formulas, the Vitamin D in breast milk is highly bioavailable. Breast milk contains substances that facilitate and enhance the absorption of nutrients.
Breastfeeding in itself is not a risk factor for Vitamin D deficiency rickets in babies. However, through a combination of inadequate exposure to sunlight and food sources of Vitamin D, lactating mothers may produce breast milk with low levels of the hormone. Additionally, infants require regular exposure to UVB radiation in sunlight for synthesis of their own Vitamin D.
