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People with mild to moderate asthma experience fewer severe asthma attacks if they take vitamin D supplements.

This review found that the average number of asthma attacks was equivalent to about one every four years in those taking vitamin D, compared to nearly one every two years in those taking a placebo. Half as many people attended hospital for asthma treatment each year when taking vitamin D (3%) compared with those not taking vitamin D (6%). These reductions were clinically and statistically significant.

There are a few unknowns still. It’s not clear if these results apply to everyone or just those with low levels of vitamin D. Also, these results apply to adults with mild to moderate asthma when taken alongside their usual asthma medication. The effects are less clear for children and those with severe asthma. As the trials used widely varying dosages of vitamin D, the optimum dose is not known.

There is currently no specific guidance for people with asthma on whether to take vitamin D, however they seem to offer the potential for reducing treatment costs.

Why was this study needed?

In the UK, 5.4 million people have asthma. This long-term condition affects children and adults and costs the NHS about £1 billion each year. Asthma attacks can be life-threatening and many people end up being admitted to hospital for treatment.

Vitamin D is an essential nutrient that keeps muscles and bones healthy. It can be obtained from food and made in the skin from exposure to sunlight. About 22% of children over 11 years and adults of all ages have low levels of vitamin D in their blood. This is not the same as having a deficiency, with symptoms, but signifies people at greater risk of developing a deficiency. Public Health England report that low levels of vitamin D are common  and recommends that everyone in the UK (including those without asthma) considers taking a 10microgram dose of vitamin D daily, especially in winter.

This review aimed to get a clearer picture of how vitamin D supplements could help manage asthma symptoms by reviewing the strongest evidence available.

What did this study do?

This was a Cochrane systematic review of nine double-blind, randomised, placebo-controlled trials of 1093 people that measured the effects of vitamin D on asthma. Vitamin D was taken alongside normal asthma treatment for between four and 12 months.

The reviewers pooled the results of similar trials for each outcome.

This was a high quality review and the trials had a low risk of bias. However, there were several differences between the trials, which limit direct applicability. The majority of participants had mild to moderate asthma, with variable regular use of inhaled steroids. Vitamin D doses also varied between trials with some using daily regimes and others monthly injections. Baseline vitamin D levels were not recorded in most trials so we do not know how many people had a deficiency or whether there was a stronger effect for those that did.

What did it find?

  • Vitamin D supplements reduced the average number of asthma attacks requiring oral steroids from 0.44 per year to 0.28 per year (three trials, 22 children and 658 adults). This equates to a reduction from nearly one every two years to about one every four years (rate ratio [RR] 0.63, 95% confidence interval [CI] 0.45 to 0.88).
  • Fewer people taking vitamin D supplements had an asthma attack severe enough that they visited an emergency department or were admitted to hospital or both (odds ratio 0.39, 95% CI 0.19 to 0.78, seven trials, 307 children, 658 adults). Over a period of eight months, vitamin D reduced the rate from 6 in 100 people to 3 in 100 people (95% CI 1 to 5). Results were mostly based on adults as there were few events in the child trials.
  • Lung function and daily symptoms were unchanged by vitamin D supplements.
  • Vitamin D did not cause any increase in serious adverse events.

What does current guidance say on this issue?

The British Thoracic Society 2016 guideline on the management of asthma does not include advice on vitamin D.

NICE advises health professionals to recommend vitamin D supplements for people at risk of deficiency. This includes children under the age of five, pregnant and breastfeeding women, people with low skin exposure to the sun and those with darker skin.

From July this year (2016) Public Health England advise that everyone needs vitamin D equivalent to an average daily intake of 10 micrograms to protect bone and muscle health. This, they say can come from, natural food sources, fortified foods (including infant formula milk) or supplements.

What are the implications?

Preventing asthma attacks not only improves quality of life but reduces the risk of serious consequences, including death. This review of the best available evidence suggests taking a vitamin D supplement alongside usual medication can reduce the number of exacerbations or attacks.

However before clinical recommendations can be made, it would be nice to know the optimum dosage of vitamin D supplements and who is likely to benefit most, taking into consideration age, severity of asthma, and baseline vitamin D levels.

Citation and Funding

Martineau AR, Cates CJ, Urashima M, et al. Vitamin D for the management of asthma. Cochrane Database Syst Rev. 2016;9:CD011511.

Cochrane UK and the Cochrane Airways Group are supported by NIHR infrastructure funding.


BTS. British guideline on the management of asthma: A national clinical guideline. London. British Thoracic Society and Scottish Intercollegiate Guidelines Network.

NHS Choices. Vitamins and minerals – vitamin D. London: Department of Health; 2015.

NICE. Vitamin D: Increasing supplement use in at risk groups. PH56. London. National Institute for Health and Care Excellence; 2014.

NICE. NICE support for commissioners and others using the quality standard for asthma. QS25. London: National Institute for Health and Care Excellence; 2013.

SACN. Vitamin D and health. London: Public Health England, Scientific Advisory Committee on Nutrition; 2016.

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All studies in this review administered oral vitamin D3 (cholecalciferol) to participants in the intervention arm. The vitamin D dosage regimens differed between trials:

  • Four studies used exclusively daily dosing regimens ranging from 500 IU/day to 1200 IU/day.
  • One study used weekly dosing
  • One study used monthly dosing
  • One study used two-monthly dosing
  • Two studies gave a bolus dose at the start of the study, followed by daily dosing

Ten micrograms is equivalent to 400 IU vitamin D3 (international Units), so these trials used supplementation that was more than the current reference nutrient intake (RNI).


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