Researchers call US RDA inadequate for nursing mothers to ensure optimal vitamin D levels in their infants
by Craig Weatherby
Vitamin D is produced in the skin when it is hit by sunlight, but this provides optimal blood levels only among people living in sunny, tropical latitudes.
Researchers now concur that the current US dietary recommendations for vitamin D intake—400 international units (IU) per day—are woefully inadequate.
Most believe that people dwelling in the world's temperate zones (i.e., much of America and Europe) should be taking 1,000 to 2,000 IU of vitamin D3 per day, and about twice as much during dim winter months.
And the results of a study conducted in nursing women suggests that they should probably be taking ten times the US RDA in order to ensure that their infants get enough of this critical nutrient.
As the researchers said, “The daily recommended intake for vitamin D during lactation has been arbitrarily set at 400 IU/day. This recommendation is irrelevant with respect to maintaining the nutritional vitamin D status of mothers and nursing infants, especially among darkly pigmented individuals.”
Inadequate vitamin D may worsen children's future health
Researchers from the Medical University of South Carolina conducted the study because they knew that mothers who consume only the US RDA (400 IU)—especially darker-skinned women—cannot sustain vitamin D blood levels adequate to ensure prevention of rickets (malformed bones) in their nursing infants.
In fact, the incidence of rickets may be on the rise in the US, especially among exclusively breast-fed African-American children.
According to a 2001 report by the US Centers for Disease Control and Prevention, which found seven cases in Georgia, “There are no national rates for rickets because it is not a reportable public health disease, and there are no surveillance systems that capture information about it. The Georgia cases probably represent only part of the true prevalence of rickets, as the study only reviewed cases of children who were hospitalized.”
But we now know that vitamin D plays a much bigger role in preventive health, beyond preventing rickets.
In addition to evidence that higher vitamin D levels help prevent heart disease, osteoporosis, cancer, flu infections, and diabetes in adults (go to our newsletter archive and search for vitamin D), studies from sunlight-deprived Finland also link vitamin D supplementation in childhood with reduced risk of diabetes in adulthood.
This new understanding implies that intake levels among children and adults alike should be raised well above the minimal, US RDA levels needed to prevent rickets.
Findings indicate higher vitamin D intakes needed
To test the effects of higher maternal intake levels on the vitamin D levels of nursing infants, a team from the Medical University of South Carolina recruited 18 nursing mothers.
They divided the nursing mothers into two groups and gave them differing amounts of supplemental vitamin D for three months, beginning one month after they'd given birth:
- The lower-dose group received 2,000 IU per day (400 IU as vitamin D3 and 1,600 IU as vitamin D2).
- The higher-dose group received 4,000 IU per day (400 IU as vitamin D3 and 3,600 IU as vitamin D2).
Note: Vitamin D3 is the form found in fish and a few other animal foods, and it is the most effective kind. Vitamin D2 is a less effective form of the vitamin, yet it is the kind used in many supplements.
Both supplementation regimens increased the vitamin D levels of the mothers and infants, but the higher-dose group showed correspondingly higher, healthier blood levels.
In addition, the “anti-rickets” activity of milk from the higher-dose group was substantially higher than milk from the lower-dose group.
The South Carolina team concluded that nursing mothers need to take at least 2000 IU per day, and that it would be ideal for them to take 4,000 IU per day, to raise vitamin D levels in their nursing infants to optimal levels.
And this intake level would be perfectly safe. As they noted, studies among normal adults demonstrate that vitamin D intakes of up to 10,000 IU per day for 5 months are safe, with no evidence of toxicity.
As they said, this step “…could achieve substantial progress toward improving both maternal and neonatal nutritional vitamin D status.”
- Hollis BW, Wagner CL. Assessment of dietary vitamin D requirements during pregnancy and lactation. Am J Clin Nutr. 2004 May;79(5):717-26. Review.
- Hollis BW, Wagner CL. Vitamin D requirements during lactation: high-dose maternal supplementation as therapy to prevent hypovitaminosis D for both the mother and the nursing infant. Am J Clin Nutr. 2004 Dec;80(6 Suppl):1752S-8S.
- Hypponen E, Sovio U, Wjst M, Patel S, Pekkanen J, Hartikainen AL, Jarvelinb MR. Infant vitamin d supplementation and allergic conditions in adulthood: northern Finland birth cohort 1966. Ann N Y Acad Sci. 2004 Dec;1037:84-95.
- Hypponen E, Laara E, Reunanen A, Jarvelin MR, Virtanen SM. Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study. Lancet. 2001 Nov 3;358(9292):1500-3.
- McGrath J, Saari K, Hakko H, Jokelainen J, Jones P, Jarvelin MR, Chant D, Isohanni M. Vitamin D supplementation during the first year of life and risk of schizophrenia: a Finnish birth cohort study. Schizophr Res. 2004 Apr 1;67(2-3):237-45.
- US Centers for Disease Control and Prevention. CDC identifies nutritional deficiencies among young children. Accessed online January 4, 2006 at http://www.cdc.gov/OD/OC/MEDIA/pressrel/r010330.htm