Children Receive Well Over RDA
for Most Vitamins

The NIH Office of Dietary Supplements, working in concert with the National Library of Medicine, recently created the Dietary Supplement Label Database (DSLD) to allow researchers to access and analyze supplement label information to, among other research goals, ensure that the information on supplement labels is truthful and accurate.

Now the first published analysis using the database to look specifically at supplemental vitamins for infants and children one to four years old has found that children's supplements almost universally contain more than the recommended daily allowance for vitamins. The findings were published in January in JAMA Pediatrics.

Some 172 labels of vitamin supplements geared toward infants and children up to age four were compared with the Institute of Medicine (IOM) recommendations for vitamin intake. On average, supplements contained more than the recommended daily allowance of every vitamin except D and choline. The amount of biotin in supplements exceeded the recommended daily allowance or adequate intake level by five to 10 times, with the highest incidence discovered at an astonishing 936% of adequate intake level.

Based on this analysis, it's clear that much of pediatric vitamin supplementation is not based on IOM recommendations and represents an unsettling tendency toward oversupplementation. More testing and careful monitoring of supplemental vitamin dosage levels for two of our most vulnerable demographics—babies and very young children—needs to be mandated and is likely to follow.

Vitamin D can be a challenge, however. Interestingly, vitamin D was only one of two vitamins that did not exceed the recommended daily allowance/adequate intake level set forth by the IOM. Indeed, the National Center for Health Data, which compiles and dispenses statistics on the nation’s health, reported a few years ago that nearly one in three Americans has vitamin D blood levels below the threshold that the IOM says is needed for good bone health.

Vitamin D is a tricky nutrient to obtain through diet alone—few foods contain it naturally. Many doctors recommend taking 800 IU of vitamin D3 a day. But it’s also produced by the body in a complex process that starts when rays of ultraviolet B (UVB) are absorbed by the skin. The liver and kidneys are then involved in making available the form of vitamin D that the body can use. Now, a Swedish medical journal reports other factors that influence vitamin D level. Given that so many people are low in vitamin D, it’s worth looking closely at these factors.

Northern exposure. At higher latitudes, the amount of UVB light reaching the earth’s surface goes down in winter. This is because of the low angle of the sun. Short days combined with cold-weather clothing covering legs and arms make UVB exposure limited at best from November through February, which in turn results in low vitamin D levels.

Air quality. Burning fossil fuels and wood scatters UVB rays, as well as absorbs them, by producing carbon. This reduces the amount of vitamin D you manufacture. Interestingly, however, the ozone absorbs UVB, so holes in the ozone layer caused by pollution may enhance your vitamin D levels by letting more UVB through.

Sunscreen? Not really. Though it prevents UVB from penetrating your skin, studies of sunscreen’s effects in practice have shown that its adverse influence on vitamin D are minimal. Most people do not apply enough sunscreen to block all UVB, or they simply use it in an irregular way that allows some UVB exposure. An often-cited Australian study showed no difference in vitamin D between adults randomly assigned to use sunscreen and those given a placebo cream.

Skin tone. Melanin is the substance in skin that makes it dark. It “competes” for UVB with the substance in the skin that kick starts the body’s vitamin D production. As a result, dark-skinned people tend to require more UVB exposure than light-skinned people to generate the same amount of vitamin D.

Skin temperature. Warm skin is a more efficient producer of vitamin D than cool skin. This doubles down on summer’s effect on vitamin D production, since the sun’s rays are already more powerful and longer lasting during summer’s long days. The added heat facilitates the production of more vitamin D than temperatures on a cool day.

Body fat. One frequently overlooked factor is that fat tissue soaks up and stores vitamin D, making it a kind of rainy-day fund for the substance. But other research has shown that being obese is correlated with low vitamin D levels, and that being overweight may affect the bioavailability of vitamin D. It’s unclear how these factors ultimately play out in the balance of vitamin D production, but, much like sun block’s protection from melanoma, it goes without saying that there are myriad reasons beyond effect on vitamin D that merit keeping a healthy body weight.

Age. Older people have lower levels of the skin’s conversion substance for making vitamin D than do those under 40. There’s also experimental evidence that older people are less efficient vitamin D producers than younger people. Still, the National Center for Health Statistics data on vitamin D levels does little to buttress the conventional wisdom that older folks are any more vitamin D deficient than younger people. There just isn’t a statistical drop-off after 50 in the way you’d expect if there were a significant inadequacy by age.

Liver health. Some types of liver disease can reduce absorption of vitamin D because the ailing liver isn’t producing normal amounts of bile. With other types, steps essential to vitamin D metabolism occur incompletely or not at all. Kidney health matters too. Levels of the bioactive form of vitamin D tend to track with the health of the kidneys, so in someone with kidney disease, bioactive vitamin D levels decrease as the disease gets worse, and in end-stage kidney disease, the level is undetectable.

Consumption of fortified dairy products like milk, which has vitamin D added to it in part because of D’s role in calcium absorption, falls off after childhood. Given how chronically undernourished we are in vitamin D, a conversation with your doctor about whether supplementing vitamin D is appropriate is certainly one worth having.

JAMA Pediatrics, Research Letter, Jan. 27, 2014, http://archpedi.jamanetwork.com/article.aspx?articleid=1815477

Harvard Health Beat, Aug. 2011, http://tinyurl.com/4239l62

CDC&P, http://www.cdc.gov/nchs/

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