Asthma is a chronic disease of the lung that causes inflammation and constriction in the airways. Affecting more than 300 million people across the world, this respiratory disorder causes recurring episodes of wheezing, coughing, chest tightness, and shortness of breath. The severity of these symptoms may range from mild to severe flare-ups (exacerbations may require immediate medical attention.)
Unfortunately, there is no cure for asthma. Conventional treatment mostly centres on providing quick-relief in severe attacks, preventing symptoms from becoming worse and reducing the frequency of severe attacks in the future.
Link between vitamin D levels and asthma
Can low levels of vitamin D increase your risk of asthma or allergies? Over the years, many studies have linked poor vitamin D status with increased risk of asthma attacks, reduced lung function, increased dependence on medication, and exacerbations in both adults and children.
This 2014 study revealed that “vitamin D deficiency was a strong correlate for asthma, allergic rhinitis and wheezing” in children. 
In addition, vitamin D deficiency in pregnant women is associated with a high risk of lower respiratory tract infection in infants during the first year of life. It also raises the risk of developing asthma, wheezing disorders, eczema, atopic dermatitis and allergies in young children.
Can taking vitamin D lower the risk of asthma attacks?
A 2015 review highlights the effect of vitamin D on lung development and the immune system, that may play an important role in the development and severity of allergic conditions such as asthma, eczema and food allergy. 
Vitamin D may help reduce the severity of asthma and allergies through a variety of mechanisms, including:
- Regulatory effects on the innate and adaptive immunity
- Preventing respiratory infections, like cold and flu, that can aggravate asthma symptoms
- Reducing inflammation
- Effects on lung function, development and growth
- Reduced the rate of exacerbations that require treatment with corticosteroids
- Decreased the risk of asthma attack requiring an emergency department visit or hospitalisation or both
A recent 2017 review of 25 randomised controlled trials found that: 
- Vitamin D supplementation prevents acute respiratory tract infections, such as cold and flu, known to trigger severe asthma attacks in patients. This strategy offers greater benefit to those with severe vitamin D deficiency
- daily or weekly supplements are helpful
The researchers believe that one of the mechanisms through which vitamin D protects against respiratory infections is by increasing the production of antimicrobial proteins in the lungs. These proteins work as natural antibiotics in the body.
In the past, other studies have also demonstrated that increased intake of vitamin D during pregnancy may reduce the risk of recurrent wheezing, asthma and food allergies in early childhood.   
It is true that more studies and evidence are required to establish the exact role of vitamin D on the development and severity of allergies and asthma. There is also not enough clarity on the optimal dose and level of vitamin D required to reduce the occurrence of these diseases.
However, the evidence so far gives a clear indication that vitamin D can work as a safe, effective strategy to manage and prevent recurring episodes of asthma. It is not recommended that you discontinue the traditional treatment entirely, but including vitamin D supplements as a part of the overall treatment strategy may have several benefits for asthma patients.
Always consult your healthcare practitioner before taking any nutritional supplement, especially if you are suffering from a long-term medical condition and are taking any prescribed medication.
- Bener et al. The impact of Vitamin D deficiency on asthma, allergic rhinitis and wheezing in children: An emerging public health problem. J Family Community Med. 2014
- Hooman Mirzakhani et al. Vitamin D and the development of allergic disease: how important is it? Clin Exp Allergy. 2015.
- Martineau et al. Vitamin D for the management of asthma. Cochrane Library. 2016.
- Martineau et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ, 2017
- Camargo CA Jr1, Rifas-Shiman SL, Litonjua AA, Rich-Edwards JW, Weiss ST, Gold DR, Kleinman K, Gillman MW. Maternal intake of vitamin D during pregnancy and risk of recurrent wheeze in children at 3 y of age. Am J Clin Nutr. 2007 Mar;85(3):788-95.
- Devereux G1, Litonjua AA, Turner SW, Craig LC, McNeill G, Martindale S, Helms PJ, Seaton A, Weiss ST. Maternal vitamin D intake during pregnancy and early childhood wheezing. Am J Clin Nutr. 2007 Mar;85(3):853-9.
- Finkel et al. Adequate Vitamin D3 Supplementation During Pregnancy: Decreasing the Prevalence of Asthma and Food Allergies. Matern Pediatr Nutr. 2015; 2(1): 105.