We get about 90% of our vitamin D* via sunlight and the rest comes from diet—egg yolk, oily fish and vitamin D fortified dairy products. How, then, does one explain that more than half of people living in places where there's a lot of exposure to sunshine, like Hawaii, have lab values that declare they are deficient in vitamin D?

Regarding asthma (reactive airway disease) and allergies, observational studies are inconclusive. Here's one such study, but first and last, why there was no clear definition of what is a normal circulating vitamin D level, control group, control for socioeconomic status differences, or crossover design.

Serum vitamin D levels are inversely related to markers of allergies—serum total IgE levels and eosinophilia counts, and reactive airway disease manifestations—airway hyperresponsiveness, and/or hospitalizations for asthma, but not the gold standard, the mean forced expiratory volume in 1 second. How can that be?

Study Highlights

• The study participants were 616 asthmatic Costa Rican children between the ages of 6 and 14 years of age.

• Researchers adjusted the study results to account for potential confounders— body mass index, age, sex, and parental educational levels.

• 91% of participants had an unscheduled medical visit for asthma in the past year. Nevertheless, only 39% had received the mainstay of asthma treatment in the last year, which is the use of an anti-inflammatory medication.

• Findings: As defined above, 3.4% of participants had vitamin D deficiency; 24.6% were vitamin D insufficient.

• The more the serum vitamin D levels, the lower some of the markers of allergy: i.e., less airway hyperresponsiveness on methacholine challenge tests; less dust mite skin test reactivity; lower risk for hospitalization for asthma in the previous year; for each 10-ng/mL increase in 25(OH)D levels in an average male subject, serum total IgE levels fell by 25 IU/mL; eosinophil counts fell by 29 cells/m3

• Finally, in full confirmatory analysis, vitamin D levels were unrelated to the use of anti-inflammatory medications. Reference: Am J Respir Crit Care Med. May 1, 2009;179:739-742, 765-771.

^{[* Vitamin D deficiency herein was defined as levels of 25(OH)D less than 20 ng/mL, and levels between 20 and 30 ng/mL indicated insufficient vitamin D.]}

 

In the same Journal, Graham Devereux, MD (Aberdeen, UK) said: "Studies that supplement with the currently recommended doses of vitamin D, while unlikely to raise ethical or regulatory concerns, would fail to address the scientific evidence that larger vitamin D intakes (e.g., 2,000 IU/d) may be required for beneficial nonskeletal effects.... While these concerns may be satisfactorily addressed, it remains to be seen whether pregnant women, parents, or patients will be similarly convinced and participate in such studies. Ultimately, it is only by investigating the effects of vitamin D in doses at, and above those currently recommended, that decisions can be made on the optimal intake of vitamin D for health and the possible prevention and treatment of asthma."

Regardless, the final word about vitamin D is not in. Just remember, there's no free lunch, but judicious use of sunlight—why not?