A review of studies published in September 2016 suggests that taking vitamin D supplements and maintaining specific levels of vitamin D may help to reduce severe asthma attacks. The Cochrane Review, a collaboration of an international network of researchers who review medical evidence, found compelling evidence from a number of randomized trials to support the recommendation.
The review of international trials involving countries including the U.S., Canada, India, Japan, Poland, and Great Britain found that vitamin D supplements reduced the number of severe asthma attacks that required hospital treatment to around three to six percent. This finding applied only to patients with mild to moderate disease, but it did not apply to patients with more severe forms of asthma.
Another finding was that vitamin D supplementation reduced the rate of asthma attacks needing treatment with oral steroids. Vitamin D did not improve day-to-day asthma symptoms.
This was a review of seven trials that involved 435 children and two trials with 658 adult patients who were followed over a period of six to 12 months.
The research review established the finding that low blood levels of vitamin D has been associated with increased risk of asthma attacks. Unlike previous large studies of asthma, this review included studies that involved many different ethnic groups.
So taking vitamin D supplements in addition to standard asthma treatments ** seems to reduce severe asthma attacks in mild to moderate adult asthmatics, who have low levels of vitamin D**, without causing any negative side effects.
What’s not clear, however, is whether these benefits (from taking vitamin D supplements) occur only in those with a pre-existing deficiency of vitamin D. Your body makes vitamin D when it is exposed to sunlight (and a precursor in your skin is converted into D3). You also can obtain vitamin D if you eat foods that naturally contain vitamin D or are fortified with vitamin D, or by taking vitamin D supplements. Vitamin D is typically ample in the western diet (thanks to fortified foods). Many people, however, do not consume adequate vitamin D and live in countries with winter seasons that offer scant sunlight, so they are especially prone to low levels of vitamin D.
Health care providers have only recently started to check for Vitamin D levels in patients, and a large number of individuals have been found to have lower than normal levels, in spite of taking supplements.
Should you check your vitamin D level?
Vitamin D is important for the regulation of calcium and phosphorous absorption, maintenance of healthy bones and teeth, and it may protect against multiple diseases and health conditions. It’s important to be aware of your vitamin D level, but unfortunately it is a more expensive test that is not always covered by insurance, so it’s not done routinely. The test measures 25(OH)D. If your doctor has reason to suspect low levels, he or she can order the test, and insurance will most likely then cover the cost.
How is vitamin D linked to asthma?
As mentioned, vitamin D is involved in the absorption of calcium, so a deficiency will impact the integrity of the musculoskeletal system and growth in general. There is a theory that vitamin D has an effect on aspects of the immune system, which might be relevant in the primary prevention of asthma. This theory was confirmed by studies that showed that individuals, with mild to moderate asthma that is “poorly controlled,” were found to have reduced vitamin D levels.
Other findings in the Cochrane Review showed that lower levels of vitamin D were also associated with high BMI (body mass index) and obesity.
Those with low levels of vitamin D also had higher levels of inflammation, shown by elevated levels of nitrous oxide inhalation and sputum eosinophils, known markers of airway inflammation. Eosinophils are found to be elevated in a number of conditions that have an inflammatory component including allergies, parasitic infections, and some pneumonias.
Vitamin D metabolism is also influenced by melanin content of the skin, which may help to explain the worse outcomes of asthma in African-Americans.
Obesity has been demonstrated to increase asthma risk, and one of the most significant effects of obesity in asthma is that it seems to impair response to steroids (a hallmark treatment in asthma). On the other hand, higher levels of vitamin D are associated with an improved response to steroids.
Some cautionary points to consider
Always discuss use of supplements with your doctor.
The Cochrane Review only showed improvement in adults with mild to moderate disease. Individuals who have severe disease should discuss any possible merits of vitamin D supplementation with their doctor until more research is done.
Taking excess vitamin D can have serious consequences. Unlike other water soluble vitamins, where excess gets dissolved in the urine and excreted, vitamin D is a fat-soluble vitamin, which means excess is stored in the body. Excess can result in side effects, including kidney stones. Always check your vitamin D level to be sure that you either need vitamin D or to make sure you are taking the appropriate dose.
Most dermatologists recommend a few 20 minute exposures to sunlight weekly without the use of sunblock (which prevents the synthesis of vitamin D). Given the risk of skin cancer and the risk of oxidative stress from excessive sun exposure, check with your doctor to make sure this level of sun exposure is safe. In this case, “more is not better” when discussing sun exposure, given the risk of skin cancer.
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Eli Hendel, M.D. is a board-certified Internist and pulmonary specialist with board certification in Sleep Medicine. He is an Assistant Clinical Professor of Medicine at Keck-University of Southern California School of Medicine, and Qualified Medical Examiner for the State of California Department of Industrial Relations. His areas of expertise in private practice include asthma, COPD, sleep disorders, obstructive sleep apnea, and occupational lung diseases.