Vitamin D study raises further questions
12 May 2009

A recent study revealing a link between low levels of vitamin D and severe asthma symptoms in children has highlighted conflicting research into the subject.

Vitamin D is essential for healthy bones and teeth. But while some researchers believe it can protect young children from developing asthma and allergies later in life, others cite vitamin D supplements as a possible reason why asthma rates have risen over the past few decades.

In this latest study, American researchers studied 616 children in Costa Rica and found that children with lower vitamin D levels were significantly more likely to have been hospitalised for asthma in the previous year. These children were also significantly more likely to have several allergies.

However, as other scientists point out, low vitamin D is intimately linked to poverty, poor diet and lack of healthcare, all of which might contribute to severe symptoms.

Previous studies also have found that vitamin D might offer some protection against asthma. Two studies published in 2007, one American and one from Aberdeen, both found that children of women with increased dietary intake of vitamin D during pregnancy are less likely to wheeze, suggesting that their risk of asthma might also be reduced. American researchers also discovered that the less vitamin D an individual has in their blood, the greater their risk of developing chest infections, a common cause of asthma attacks.

However, a recent UK research study found that children of women with high levels of vitamin D when they gave birth had a greater risk of eczema and asthma, which suggests vitamin D might in some way increase asthma risk.

Less controversially, there is evidence that vitamin D might increase the effectiveness of steroid treatments for asthma. An Asthma UK-funded study, led by Dr Catherine Hawrylowicz, is aiming to discover whether taking vitamin D tablets alongside steroids can help people with asthma keep their symptoms under control.

Dr Hawrylowicz, who is based at the MRC-Asthma UK Centre in Allergic Mechanisms of Asthma, said: ‘Research studies over the years generally suggest that vitamin D is likely to be beneficial for lung health. However, there is conflicting evidence over the amount of vitamin D that we need to stay healthy, and how vitamin D might impact on asthma. What we need now are clinical trials in which pregnant women, and people with asthma, are given vitamin D supplements to find out whether this is a useful way to prevent asthma or reduce asthma symptoms.’