- Vitamin D is a micronutrient that contributes to bone health and calcium metabolism.
- A previous Cochrane review indicated that vitamin D might help reduce the risk of asthma exacerbations.
- Data from the 2023 Cochrane review indicates that vitamin D doesn’t help reduce the risk of asthma exacerbations.
- Further research is warranted to confirm the review’s findings.
Vitamin D is a nutrient that is a critical component of health. Researchers are still working to understand the full benefits of vitamin D and how taking the vitamin impacts various areas of health.
Previously, researchers thought that vitamin D helped protect against asthma attacks.
However, the latest review published in the Cochrane Database of Systematic Reviews found that taking vitamin D likely doesn’t help improve asthma symptoms or reduce the risk for asthma attacks.
This review does not negate the other health benefits of vitamin D.
Lisa Richards, nutritionist and creator of the Candida Diet, who was not involved in the study, elaborated to Medical News Today why vitamin D was rising in popularity:
“Vitamin D is becoming popular because of its immune support benefits that have been observed. The active form of vitamin D will help to mitigate the body’s inflammatory response and boosts the body’s immune cell production.”
“Vitamin D is essential to allowing your body to use the calcium it is given to support bone growth and health. When vitamin D levels are low, this process is not as efficient, and our bones can become weak,” she added.
Researchers have been interested in studying a variety of the health effects of vitamin D. For example, there has been research on vitamin D and its potential role in preventing adverse health outcomes like cancer,
One area of interest is how vitamin D may benefit people with asthma.
In a 2016 Cochrane review, the results from several studies suggested that vitamin D could help protect against asthma attacks.
New data has emerged since this review, and researchers sought to re-evaluate the research and how it compared to previous findings.
Researchers in this current review sought to see if vitamin D helped reduce risks of asthma exacerbations or helped improve control of asthma symptoms. Asthma exacerbations meant that symptoms were bad enough to require treatment with systemic corticosteroids. The analysis was similar to the review conducted in 2016.
Review author Adrian Martineau, professor of respiratory infection and immunity at the Blizard Institute, Queen Mary University of London, noted that they used the “Same methodology, but [the] latest review includes data from more trials so we can be more confident in the result.”
Researchers included double-blind, randomized, placebo-controlled trials that studied vitamin D in children and adults with asthma. They included a total of twenty studies in their analysis involving over 2,225 people with asthma.
A single study that looked at a form of vitamin D called calcidiol indicated that calcidiol could help with asthma control. However, for the majority of studies, findings indicated that vitamin D doesn’t help prevent severe asthma attacks or help control asthma symptoms when compared to a placebo. This contradicts the results of the previous review.
The review authors concluded the following:
“This updated review does not find evidence to support a role for vitamin D supplementation or its hydroxylated metabolites to reduce risk of asthma exacerbations or improve asthma control.”
Similar to the previous review, the current review has limitations and encourages continued research. Researchers note that it may be beneficial to conduct more research into calcidiol to see if this particular form of vitamin D truly has protective factors.
The studies included in the analysis did not include many participants who had severe asthma or very low vitamin D levels before taking supplements. Therefore, it’s unclear how taking vitamin D may benefit people in these groups.
Professor Martineau also offered a few potential reasons for the differences between the findings of the two reviews.
He said it could’ve been a type 1 error, where the original was a chance finding or there were improvements in asthma treatments and vitamin D intake.
“[It could be due to] improvements in background vitamin D status (more supplement use, more vitamin D-fortified foods – which elevate vitamin D status in all participants, thus fewer deficient patients at baseline who may benefit the most, thus loss of signal) [or] improvements in asthma treatment / better adherence to asthma treatment — thus less room for improvement as a result of a nutritional supplement,” he told MNT.
Lastly, he said, it could be publication bias.
“[E]arly on in the hypothesis, null trials [are] less likely to get published than positive ones. Funnel plot ([a] formal way of investigating this) did not suggest this, though,” he added.
The results of this review do not indicate that people should stop taking vitamin D or that vitamin D doesn’t offer other benefits.
People taking vitamin D can discuss its implications with their doctor and explore the potential benefits of continued use.
“[The] Implication is that vitamin D supplements don’t reduce risk of asthma attacks. If someone with asthma was taking vitamin D for this indication alone, then [the] latest review suggests this is unlikely to be justified,” said Prof. Martineau.
He also pointed out to MNT that many people with asthma take vitamin D as prevention against medication side effects.
“[A] lot of people with asthma take vitamin D to protect bone mineral density if they are taking steroid inhalers or tablets. They should not stop taking supplements on [the] basis of this review, which only examines efficacy for preventing asthma attacks and doesn’t address question[s] of bone health.”
— Prof. Adrian Martineau