In the musical world, everyone could see which Beatles song was the world’s most popular one when their catalog became available on iTunes in November 2010. During the first month of availability, ‘Here Comes The Sun’ was the most requested song.
In the medical world, some–but not excessive– sun exposure is needed for the body to make vitamin D from a cholesterol derivative in the skin. A popular medical question that has come up over the past 10+ years, especially with the Chicago winter upon us, is whether we need even more vitamin D to prevent more illnesses than just to prevent bone fractures. Or, do we rely on George’s lyrics, plus Paul’s lyrics and just “follow the sun”?
Vitamin D’s speculated role in allergic diseases first received prominent attention in a 2007 study that showed higher EpiPen prescriptions in regions further from the Equator. The suggestion was made that if there is less UVB light further away from the Equator, then there is less natural vitamin D being made in the body to prevent allergic reactions. Subsequent studies showed that babies born in autumn and winter have lower vitamin D levels in their bodies and have a higher risk of food allergy.
In 2011, the Institute of Medicine concluded that higher vitamin D levels have not shown more health benefits beyond those for protecting the bones. But, their statement did include that more targeted research is needed. Around then and since then, many observational reports have been published about associations between vitamin D and symptoms. We all need to be aware, though, that associations don’t necessarily mean causes. If people choose to walk their dogs only during the day, there can be an association between dogs being walked and daytime TV shows; but, the TV shows did not cause the dogs to be walked. Similarly, vitamin D could just be a marker of other nutrients and other habits that are the actual causes for the health effects we see.
There are some basic facts to keep in mind when hearing about these vitamin D studies. First, the vitamin D status is best assessed with a blood test that measures its metabolite called 25-hydroxyvitamin D. Then, there is a distinction between being vitamin D insufficient and vitamin D deficient. Vitamin D insufficiency is a blood level between 20 and 30 (ng/ml). Vitamin D deficiency is a blood level less than 20 (ng/ml). There are also many factors that influence interpreting the relevance of a study’s findings for a specific person, such as these: the age of the individual; the dose of vitamin D taken; the baseline vitamin D metabolite level; whether the individuals in the study lived closer to or further from the Equator.
Among the publications about vitamin D’s health benefits for allergic diseases, the topic most often and most rigorously studied has been in the area of asthma. Some, but not all, studies show associations between having a low vitamin D and having a higher risk of respiratory infections. Two studies about prenatal vitamin D supplementation to prevent asthma in young children were published last year in the high- profile medical journal JAMA. The study from Denmark was significant only for less episodes of lung symptoms for those children whose mothers took supplemental vitamin D. The United States study showed a trend for less asthma or less recurrent wheezing by age 3 for those children whose mothers took a higher vitamin D supplemental dose of 4,400 IU/day.
Other studies have been published about other allergic diseases in lesser numbers. There are reports that (a) lower vitamin D levels are associated with a higher occurrence of childhood nasal/eye allergies, (b) there is a benefit from supplemental vitamin D treatment in a randomized study of patients with chronic urticaria, (c) control of atopic dermatitis (i.e. eczema) can vary with the vitamin D blood level and (d) vitamin D insufficiency is present in patients with eosinophilic esophagitis. But, not enough confirmatory or rigorously designed studies exist for experts to make new recommendations.
The scientific literature from research laboratories strongly supports the concept that vitamin D acts on immune cell function. But, the mechanisms are complex to sort out for each medical condition. The medical literature over the past 10 years seems to indicate that vitamin D deficiency (less than 20) is related to more positive tests to allergens, a higher risk for flare-ups in those with mild to moderate asthma and to a higher likelihood of ongoing eczema. The studies provide suggestive but inconclusive evidence for vitamin D insufficiency (between 20 and 30) as a cause for asthma either developing or worsening in children. There is insufficient evidence to support using vitamin D either to prevent or treat food allergy.
The conflicting and evolving data prevent a specific nutritional guideline about vitamin D for allergic diseases. What should we do? First, I think all of us need to eat foods with the appropriate levels of nutrients and enjoy more time outdoors with sensible protection from excessive ultraviolet sunlight. If there are frequent asthma flare-ups or unexplained recurrences of other allergic diseases, checking a vitamin D blood test seems appropriate. If the result is less than 20–vitamin D deficiency–supplementation is needed from dietary sources but an exact dose of a synthetic vitamin D supplement is uncertain. If the result is between 20 and 30–vitamin D insufficiency–supplementation may need to be considered. Hopefully, we will have, sooner than later, more specific and definitive advice about the right amount of vitamin D to have for preventing and treating allergic conditions. Then, we can all say… or sing: “Here comes the sun, and I say it’s all right.”