October 26, 2009 02:37 PM ET | Nancy Shute

Is my child getting enough vitamin D to stay healthy this winter? That was my question in the early morning gloom as I scanned the label of our Dora the Explorer multivitamins. The 400 IU listed meets the recommended daily value for children. But that may not be enough, according to new research from Children's Hospital Boston. How could that be? I quickly called Jonathan Mansbach, a pediatrician and coauthor of the study, to get the scoop.
About one third of the children in his study, which looked at blood levels of vitamin D in about 5,000 children, were taking multivitamins. Most of those multis, like my family's, contained 400 IU of D. But of the children taking multivitamins, 62 percent had blood levels of vitamin D below 75 nmol/L, a level increasingly thought to be a better reflection of the amount of the nutrient needed to prevent disease than the 50 nmol/L recommended by the American Academy of Pediatricians. (Ten percent of the kids taking vitamins had a D level below the AAP's recommended level.) "The conclusion there is that 400 [IU] may not be enough," says Mansbach. Good to know, but what should I do? The doctor's next sentence was not what a mother wants to hear. "What is the correct amount is kind of hard to say."
Come on, research scientists, help us parents out! But the lack of clarity on "how much D is enough" is not the researchers' fault. Rather, it's because the sense of the target level of vitamin D is rapidly shifting, supported by increasing evidence that the nutrient may protect against heart disease, some cancers, respiratory infections, childhood wheezing, and eczema.
Last year, the AAP urged that breast-fed babies get a 400 IU vitamin D supplement daily because their mothers can't provide them with enough D. Multivitamins with 400 IU of D, like the one I give my daughter, were recommended for older kids. Mansbach's research, which was published online today in Pediatrics, suggests that probably isn't enough. That's particularly true in winter, when the sun isn't strong enough for skin to make vitamin D if you're living anywhere north of Atlanta. And it's particularly true for children with darker skin, because the pigmentation that protects them from sunburn also blocks D-making rays. It's even true for pale kids like mine, because we keep them coated with sunscreen to protect them from skin cancer. Add in the fact that our children are all too often inside, in school, in day care, or watching TV, and there's no shortage of reasons why the children in the study came up so short on D. Even drinking milk doesn't fill the gap; a child would have to drink a quart of milk daily to get 400 IU. (Caveat eater: many yogurts aren't fortified with D, so check labels if yogurt is part of your vitamin D accumulation strategy.)
One of the best ways to get useful information out of a pediatrician is to ask: "What do you do for your own kid?" When I asked Mansbach that question, he said: "I give my kid 1,000 IU a day." That's for his 8-year-old, who he says has darker skin and is thus more likely to be deficient.
There's no apparent downside to giving a child 1,000 IU of vitamin D; it takes 10,000 IU a day to risk toxicity in adults. But it's still a guesstimate. "Honestly, it's really up in the air right now," Mansbach said. We won't know the answer until good randomized clinical trials are done on vitamin D dosing and its effect of disease. Some such tests are in the works. In the meantime, there's fierce debate in medical-land on whether the daily requirements for vitamin D need to be raised, for children and adults alike. In the meantime, here's a job for common sense. I'll keep dosing out the Dora vitamins but might add in some extra vitamin D—for the whole family.