KIDS

Vitamin D and Childhood Asthma – New Research

By: Dr. Hilary Jones

March 11, 2017

When I was a medical student, few people gave vitamin D a second thought. Of course, we were taught to advocate a healthy balanced diet for adults and children alike, but the accepted wisdom was that you could get all the nutrients you needed from your food as long as you ate enough of the right foods in the right quantities.

Vitamin D challenged that thinking – when exposed to sunshine, about 90 percent of the vitamin D in the average human body is made in the skin. Concerns about skin cancer, reduced outside activities and air pollution have cut our exposure to sunshine, with the result that almost 50 percent of the world’s population has inadequate levels of vitamin D in their bodies[1].

Vitamin D has long been known to play a crucial role in bone formation – helping to prevent osteoporosis in older people [2] and rickets in children [3]. In the Western world, we assumed conditions like rickets, the softening and weakening of bones, were traditionally associated with poverty and had been consigned to history – yet cases have increased dramatically even in the developed world during the 21^st Century [4].

In recent years, more evidence has come to light for a possible role of vitamin D in protecting against heart disease [5] and even type 1 diabetes [6], but nowhere has there been more excitement than in the arena of asthma.

It has long been known that being exposed to potential allergens early in life can increase the risk of developing asthma [7,8]. As far as vitamin D goes, the theory is that because vitamin D has direct and indirect effect on the actions of various cells in our immune system, it may influence the way the immune system responds both to allergens and to respiratory tract infections [9]. This in turn may play a part in modulating the role allergens, viruses and bacteria have in triggering asthma, especially in children at high risk.

In 2007, a study in Massachusetts followed a group of 1,200 mothers and their children up to the age of 3, assessing the mothers’ vitamin D intake during pregnancy and comparing it to the likelihood of their child developing a recurrent wheeze by the age of 3 [10]. They found that mothers in the highest 25 percent for vitamin D intake had children with a lower risk of a wheeze than those in the lowest 25 percent. Furthermore, the study showed that a 100 International Unit (2.5microgram) increase, whether from diet or supplements, cut the risk of a wheezy child by nearly 20 percent.

Two years later, a Costa Rican study measured blood vitamin D levels among 6-14 year olds and compared them with markers for asthma such as levels of eosinophils (a type of white blood cell associated with allergy) and IgE (an antibody used by the immune system to neutralize pathogens that is linked to a wide variety of allergic conditions). They also looked at hospital admissions for asthma, tendency of the airways to go into spasm and the need for anti-inflammatory medication for asthma. In all cases, there was an inverse relationship between vitamin D levels and these markers of asthma severity [11]. In 2010, a study looking specifically at children with asthma compared their levels of skin-prick test response to air-borne allergens, levels of steroid medication they needed, lung function and blood markers of inflammation. Again, the lower the vitamin D, the worse the lung function and the more evidence they showed of allergy and inflammation [12].

This brings us to this latest study, which followed children at a high risk of allergy from birth to the age of 10 years. The children underwent blood tests for vitamin D levels at the ages of 0.5, 1, 2, 3, 4, 5 and 10. The blood tests were then compared to known markers for sensitivity to asthma. The lower the level of vitamin D, the more likely they were to have become sensitized at the ages of 0.5, 2 and 3 years. Being deficient in vitamin D was associated with a higher risk of asthma, wheezing and eczema by the age of 10. There was also an inverse relationship between vitamin D levels and the likelihood of growth of a bacterium called streptococcus known to be associated with a higher asthma risk. Finally, there was a direct link between vitamin D levels and the first age when the child experienced a significant infection of the lower respiratory tract, another asthma risk factor [13].

Does this study tell us anything revolutionary? Not really – we have known for years that vitamin D deficiency is rampant, even among Western populations, and that vitamin D may play a part in reducing development of asthma and eczema through its effect on the immune system. However, this study was well designed, thorough and long lasting – and it adds significantly to the existing weight of evidence suggesting that our youngsters need vitamin D.