Who needs more vitamin D?

A question from Allison: “I just read that 40% of children are thought to be vitamin D deficient. How can we figure out if our child falls into that 40%? Should we give vitamin D supplements just in case? What should we do to make sure they stay vitamin D healthy?”

The honest, insider answer to these excellent questions is: we don’t know. We don’t know how much vitamin D a child ought to ingest every day, and we don’t even know what the “normal” blood levels of vitamin D should be!

Vitamin D is essential to normal bone health and normal calcium metabolism. In the most severe form, inadequate vitamin D cause rickets, with severe problems with bones and growth. We know that in the 19^th century, lack of adequate vitamin D led to widespread rickets in Europe and the United States. Vitamin D is found in very few foods; the only “natural” way for people to get enough vitamin D is through sun exposure. Human breast milk is a very poor source of vitamin D. Children at the highest risk for vitamin D deficiency are breastfed babies, children who get little sun exposure, or children with dark skin—in fact, most babies who get rickets have all three of these risk factors. Fortification of cow’s milk, along with a shift towards bottle-feeding babies with fortified infant formulas, virtually erased rickets from the United States by the mid-1900’s. However, increased rates of of breastfeeding coupled with less sun exposure has led to a resurgence. The prevalence of rickets is far lower than it was years ago, but it is increasing.

Although our understanding of the role of vitamin D is incomplete, we know that higher levels of this vitamin seem to protect against diabetes, hypertension, and some cancers. The “sunshine vitamin” is important to many body systems, not just the bones.

You would think that we’d have a good understanding of exactly how much vitamin D is needed. But studies of this issue have not revealed a consistent answer. Because some vitamin D is made by the skin when exposed to sunlight, it is difficult to judge just how much needs to be ingested, given different skin tones and sunlight exposure times, plus the effect of cloudy days, seasons, or different climates. Also, ingested vitamin D occurs in a variety of forms that are absorbed and metabolized differently; and further processing in the body is needed to activate vitamin D. There are also different ways of measuring blood levels of the various forms of vitamin D, which makes it difficult to compare studies.

As with other fat-soluble vitamins, too much vitamin D is bad for your health. Increasing the intake beyond what is needed may not be a good thing. However, the exact “toxic” dose of vitamin D is not known; it is certainly much, much higher than the amount that is found in foods or ordinary vitamin D supplements.

The 40% figure Allison quoted comes from a June, 2008 article from Archives of Pediatrics. (The publisher will allow only access to the abstract to non-subscribers.) The authors looked at 365 infants and toddlers in Boston, drawing blood and performing x-rays to determine bone density. Of these kids, 12% were found to have vitamin deficiency. 40% were found to have vitamin D levels that were “suboptimal”—that is, below an “acceptable optimal threshold.” However, the blood levels chosen to define “deficient” and “suboptimal” were quite arbitrary, based on a sort of average of other similar studies. They found through x-rays that 7.5% of the children who were “deficient” in vitamin D had rickets—which, put another way, means more than 90% did not have rickets. In the same issue of that journal, a different article reviewed the many studies and controversies that have looked into vitamin D deficiency, and found that published estimates of vitamin D deficiency, depending on the definition, ranged from 1% to 78%!

The current US recommended daily allowance for vitamin D in children is 200 IU/day. There is certainly a need to reassess this figure, and perhaps adjust it upwards to 400 or even 1000 IU/day. However, at this time more information is needed to help make this decision.

Reasonable recommendations based on the best current evidence are:

• Children should get a reasonable amount of sun exposure by playing outside.
• For breastfed babies and children getting less than 16 oz of formula or milk a day, give a vitamin D supplement of 200-400 IU/day. This is especially important in situations where you can’t depend on the sun to help make vitamin D: in dark-skinned children, families who avoid sun exposure, families living in northern or cool climates, and in the wintertime.

As with other vitamin recommendations I have made, there is no reason to purchase any sort of special, name-brand, or premium vitamins. Choose one that is inexpensive, convenient, and tastes good. Since many children at risk for vitamin D deficiency are children who don’t consume milk, a combo vitamin D + calcium chocolate chewable is a good choice for many children.

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Tags: bone, calcium, mineral, rickets, sunshine, vitamin

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