Over the past decade, researchers have identified a strong association with low vitamin D levels and increased risk for asthma development and exacerbation among children and adults. Low vitamin D levels have been associated with many other health conditions as well, such as depression, cancer, and heart disease, but the first rule of thumb for trying to determine sources of health conditions is knowing that a relationship between two events does not necessarily mean that one caused the other.
Not all research studies are created equal. Despite dozens of studies investigating whether vitamin D supplementation may prevent asthma attacks, only a few have been randomized controlled trials – which is the most rigorous way to determine true cause and effect. A recent review of these limited studies was published and has been making the headlines. The studies all differed according to many key factors, including: overall outcome measure, measurement of baseline vitamin D level, age of participants, dose of vitamin D and length of time, determination of asthma severity, and location.
What is vitamin D and what does it do?
Vitamin D is a vitamin that helps our bodies absorb calcium, promote bone and cell growth, and can reduce inflammation. For asthma, it is hypothesized that vitamin D may help reduce inflammation present inside the lower airways.
We get vitamin D through two main sources: absorption of sunlight through our skin and through foods naturally high in vitamin D or fortified with it, such as milk, orange juice, and cereals. The best way to measure vitamin D levels is through a blood test, but some disagreement remains regarding the definition of vitamin D deficiency levels.
People with darker skin, who live in urban cities, or who are obese have lower levels of vitamin D. These same individuals are at highest risk for having asthma, and poorly controlled asthma. Since asthma is the most common chronic pediatric condition and a leading cause of emergency room visits and hospitalizations, the link between vitamin D and asthma absolutely merits further study.
What do we know about Vitamin D and asthma?
The authors of the recent Cochrane review concluded that vitamin D is likely to reduce risk of severe asthma attack and need for emergency room use. However, there were no differences in long term asthma control or lung function. In addition, the data from children was very small and required additional evaluation. Unfortunately, without knowing the baseline vitamin D level and other key features such as level of asthma severity, it is nearly impossible to determine which patients may benefit and at what dose.
While there appears to be a strong link between low vitamin D levels and asthma exacerbation, there are many important factors that remain unknown before we recommend supplementation as an intervention for everyone. However, it is becoming commonplace to measure baseline vitamin D levels for anyone with poorly controlled asthma, particularly if they have had prior or frequent emergency visits, have darker skin, or live in urban environments. These are likely the patients that will benefit most from vitamin D supplementation. But at what dose and for how long? That question remains to be answered.
For more information on Nationwide Children’s Hospital’s Asthma Program, click here.