Moms-to-Be: Getting Enough D May Prevent Kids’ Asthma

May 3, 2007—Asthma rates in the northeastern part of the United States are the highest in the nation—and vitamin D deficiency may be one reason, new research shows.

The body can make vitamin D, but only when skin is exposed to sunlight. Pregnant women who live in areas where sunlight is scarce are at a higher risk of vitamin D deficiency, and their children may suffer for this lack later on.

Regarding the effect of maternal diet in pregnancy on the risk of childhood asthma, Carlos A. Camargo, MD, DrPH, associate professor of Medicine & Epidemiology at the Harvard Medical School, and lead author of the new study said, “A few years ago we noted similarities between risk factors for vitamin D deficiency and risk factors for asthma. Vitamin D has many effects on the immune system, so we hypothesized that higher maternal vitamin D intakes might be protective against the development of childhood asthma.”

Camargo and colleagues studied nearly 1,200 mother–child pairs from the northeast United States. Using questionnaires, researchers assessed how much vitamin D mothers got during pregnancy. Compared with mothers with the lowest daily intake (averaging 356 IU per day), those with the highest intake (averaging 724 IU per day) had a 61% lower risk of having a child with recurrent wheezing at age three.

Vitamin D inadequacy is common in the United States, especially in northern states, due, among other reasons, to low amounts of D in the diet and low sun exposure (either because of lifestyle or overuse of sunscreen). Between November and March, people living in northern climes do not get sufficient exposure to ultraviolet (UV) rays from the sun. Studies suggest that people cannot drink enough milk to compensate for this lack. So unless they take a supplement, vitamin D deficiency is likely.

Vitamin D is also needed for calcium absorption, and is thus important for strong bones. Furthermore, it plays an important role in immune function. Several studies in recent years have shown that having adequate vitamin D levels may help prevent health conditions, including multiple sclerosis, pancreatic cancer, osteoporosis, falls in seniors, and asthma.

The officially recommended amount of dietary and supplemental vitamin D is 200 IU per day for people under 50 years old, 400 IU per day for people from 51 to 70, and 600 IU per day for people over 70. However, for individuals at higher risk of deficiency (such as those who live in northern latitudes), a daily supplement of 800 to 1,000 IU may be more appropriate. No adverse effects of vitamin D have been found in healthy people who consume up to 2,000 IU per day.

According to Dr. Camargo, more studies are needed to confirm these preliminary findings—studies he feels are warranted. “The relatively low cost and safety of vitamin D–containing foods and supplements could provide a very attractive intervention for the primary prevention of asthma.”

(Am J Clin Nutr 2007; 85:788–95)

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Jeremy Appleton, ND, CNS, is a licensed naturopathic physician, certified nutrition specialist, and published author. Dr. Appleton was the Nutrition Department Chair at the National College of Naturopathic Medicine, has served on the faculty at Bastyr University of Natural Health Sciences, and is a former Healthnotes Senior Science Editor and a founding contributor to Healthnotes Newswire. He has worked extensively in scientific and regulatory affairs in the supplement industry and is now a consultant through his company Praxis Natural Products Consulting and Wellness Services.

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