Asthma is a common illness of the lung airways, which prevents proper air entry and may cause long-term distress and death. Both children and adults are affected. The difficulty in breathing can cause alarm in both adults and children, and rarely, asthma can be fatal. A longstanding goal of asthma researchers has been to avert or prevent acute exacerbations of asthma.
Recently, researchers have pointed to the role of vitamin D deficiency in this condition.
What is vitamin D?
Vitamin D is a fat-soluble vitamin. There are two forms in the body, vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol).
Vitamin D3 is synthesized in the skin on exposure to sunlight, but can also be absorbed from oily foods or foods fortified with vitamin D, or from vitamin D supplements. Vitamin D2 is obtained from the diet, mainly in mushrooms.
Both forms of vitamin D are converted by enzymes in the body to the active form.
Vitamin D levels are therefore likely to be low during the winter in temperate countries, because of reduced sunlight exposure. Of course, the latter may happen if the skin is never exposed to sunlight, but always covered up.
What is the role of vitamin D in asthma?
Vitamin D could help in many ways to prevent asthma. For one, it is a powerful immune modulator, and also enhances antimicrobial defences in the body. Thus it could reduce the frequency of colds and other upper respiratory infections that trigger acute or severe exacerbations of asthma. In addition, it could reduce the intensity of airway inflammation that causes the wheezing and reduced air entry characteristic of this condition.
To test this, many observational and randomized trials have been carried out in a variety of settings. These were systematically reviewed, and the results show that oral vitamin D supplementation cuts the risk of severe asthma attacks which require hospital care or emergency room consultation by half, from 6% to 3%. The researchers took the rate of severe asthma attacks requiring oral steroid therapy as a proxy for asthma severity. Vitamin D brought this down from an average of once in two years to once in four years. On the other hand, there is no evidence that vitamin D improves daily symptoms or lung function, or time off from work or school. Its use is not associated with any adverse effects.
More research will be needed to extend the study findings to patients with more severe asthma, and whether vitamin D is just as effective in patients whose initial levels are normal. Moreover, the recommended dosage is still not clear. Public Health England recently advised that UK residents would benefit from taking 10 micrograms of vitamin D daily, but this is not based on scientific research. In fact, some studies used much larger doses. It might be helpful if we got our vitamin D levels tested so we could better decide whether or not to take vitamin D supplements.
For the present, asthmatics on medication should not discontinue it, even if they add vitamin D supplementation. Until further studies are available, a dose of over 100 micrograms is not advisable because excessive vitamin D can cause enhanced calcium absorption, which can damage the kidneys and the heart.
What is the mechanism of action of vitamin D in asthma?
Several mechanisms are suggested. One, lung tissue produces active form of vitamin D when it is inflamed or infected, which points to an anti-inflammatory and immune strengthening role for the vitamin. Secondly, since most asthma attacks are triggered by simple viral infections of the upper airway, such as the common cold, vitamin D may help prevent them by reducing the rates of such infections or tempering the resulting inflammatory response. In fact, both may occur as a result of vitamin D activity.
- Cochrane.org. High quality evidence suggests Vitamin D can reduce asthma attacks. www.cochrane.org/…/high-quality-evidence-suggests-vitamin-d-can-reduce-asthma-attacks
- Nhs.uk. (2016). Vitamin D 'protects against severe asthma attacks'. www.nhs.uk/…/
- The conversation (2019). Vitamin D may protect against severe asthma attacks and hospitalization. theconversation.com/vitamin-d-may-protect-against-severe-asthma-attacks-and-hospitalisation-64478
- Litonjua A. A. et al., (2007). Is vitamin D deficiency to blame for the asthma epidemic? Allergy and Clinical Immunology. https://doi.org/10.1016/j.jaci.2007.08.028
- Pfeffer P. E. et al., (2018). Vitamin D in Asthma. Chest. https://doi.org/10.1016/j.chest.2017.09.005
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Last Updated: Jul 1, 2019
Dr. Liji Thomas
Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.
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