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 intake400 international units (IU) per dayare 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 womencannot 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.

Fish have the most vitamin D;

Sockeye salmon top the rankings

Certain fish are the only substantial food sources of vitamin D, as well as being the only substantial food source of marine omega-3s, which are also critical to optimal heart health.

Among fish, Pacific sockeye salmon are the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:

Vitamin D per 3.5 ounce serving*

Sockeye salmon687 IU

Albacore tuna544 IU

Silver salmon430 IU

King salmon236 IU

Sardines222 IU

Sablefish169 IU

Halibut162 IU

*For our full test results, click here.

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.”


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  • US Centers for Disease Control and Prevention. CDC identifies nutritional deficiencies among young children. Accessed online January 4, 2006 at