Is Vitamin D Deficiency Tied to Asthma and Allergies?

Man blowing nose at home on couch
Not getting enough vitamin D can worsen allergies and asthma. Paul Bradbury/OJO Images/Getty Images

Vitamin D is an important nutrient and hormone that is found naturally in only a few foods (oily fish, cod liver oil, egg yolks) but is also made in the skin with sunlight exposure. Many foods are also fortified with vitamin D, including breakfast cereals, milk, and other dairy products. Vitamin D serves many important functions, particularly bone health (for the prevention of rickets and osteomalacia).

Vitamin D also appears to serve multiple important functions for the immune system. It acts to stimulate the immune system against various infections, such as tuberculosis, and may help prevent such diseases as colon, prostate, and breast cancer, as well as autoimmune diseases such as multiple sclerosis and type 1 diabetes mellitus. Recent studies suggest that vitamin D plays an important role in the prevention of various allergic diseases, by activating certain regulatory immune cells that prevent the release of chemicals that cause and worsen allergic diseases.

Allergic diseases of nearly all types, including asthma, allergic rhinitis, food allergies, eczema and even anaphylaxis have become much more common over the past few decades. This could be partially explained by the hygiene hypothesis, but some experts think that this is also related to vitamin D deficiency. Many studies suggest that vitamin D deficiency is extremely common; not necessarily to the degree that bone health is affected, but to the extent that the immune system is affected.

The reasons for widespread vitamin D deficiencies in various populations are not completely understood, but researchers think this is due to modern lifestyles that include more time spent indoors with less sunlight exposure, as well as the widespread use of sunscreen. These habits, along with the concern for ultraviolet radiation from sunlight (leading to skin cancers), have led to the decreased production of vitamin D in the skin of many people.

It appears that there is a relationship between low levels of vitamin D and the occurrence of allergic diseases. Anaphylaxis to various triggers (such as foods, medicines, and insect stings) occurs at much higher rates in areas with less sun exposure (northern climates). Asthma, eczema, and atopy have been associated with low vitamin D levels, particularly for people who have mutations in their vitamin D receptor genes. Vitamin D supplementation given to pregnant women significantly reduced the occurrence of asthma and other allergic diseases in young children.

It is not known exactly how much vitamin D is needed for good immune function, but most people in developed countries get enough vitamin D for healthy bones. It is possible to overdose on vitamin D, with the main side effect being kidney stones, so it is important to talk with your doctor before taking any vitamin D supplementation. Vitamin D might be best obtained by getting a reasonable amount of sun exposure, such as 15 minutes a day for two to three days a week (as suggested by some experts).

One thing is for sure: Humans were not meant to spend their entire lives indoors, so get outside and enjoy some sunshine on a regular basis. But like anything else, moderation is key, so don’t overdo it.


Taback SP, Simons ER. Anaphyalxis and Vitamin D: A role for the sunshine hormone? J Allergy Clin Immunol. 2007;120:128-130.

Litonjua AA, Weiss ST. Is Vitamin D Deficiency to Blame for the Asthma Epidemic? J Allergy Clin Immunol. 2007;120:1031-5.

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