Is Vitamin D Deficiency Linked to Allergies?

Vitamin D serves multiple important functions in the immune system. For instance, it acts to stimulate the immune system against various infections, such as tuberculosis and may help prevent certain types of cancer, or even autoimmune diseases like multiple sclerosis (although, this is all still being studied). 

In addition, studies suggest that vitamin D may play an important role in the prevention of various allergic diseases.

Allergies and Vitamin D

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.

To support this link, scientific evidence shows that food allergies and anaphylaxis occur at much higher rates in areas with less sun exposure (higher latitudes).

In addition, asthma, eczema, and atopy have been associated with low vitamin D levels, particularly for people who have mutations in their vitamin D receptor genes. Also, vitamin D supplementation given to pregnant women significantly reduced the occurrence of asthma and recurrent wheeze in young children.

Furthermore, research shows that vitamin D can activate certain regulatory immune system cells that prevent the release of chemicals that cause and worsen allergic diseases. So a deficiency in vitamin D may inhibit this regulatory mechanism, which may worsen or trigger allergic disease.

This all being said, it's important to not over-simplify the development of diseases, including allergic diseases, which are likely complex, involving both a person's genes and environment. Instead, the big picture here is that a vitamin D deficiency may play a role in a person's allergies, although exactly how much, still leaves experts scratching their heads. 

Why Does Vitamin D Deficiency Exist?

Many studies suggest that vitamin D deficiency is extremely common, not necessarily to the degree that bone health is affected (vitamin D prevents bone diseases like rickets and osteomalacia), but to the extent that the immune system is affected.

The reasons for widespread vitamin D deficiencies in various populations are not completely understood. Many researchers attribute vitamin D deficiency to modern lifestyles that include more time spent indoors with less sunlight exposure, as well as the widespread use of sunscreen (due to a concern for skin cancer). Remember, vitamin D is made in the skin with sunlight exposure—so sunscreen and an indoor lifestyle will prevent vitamin D synthesis.

Diet may be another explanation for the deficiency. Vitamin D is an important nutrient but is found naturally in only a few foods (for example, oily fish, cod liver oil, egg yolks). That being said, many foods are fortified with vitamin D, including breakfast cereals, milk, and other dairy products. Still, even with fortification, many people still do not get enough vitamin D.

How Much Vitamin D Do You Need?

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.

While there is still debate among experts on what a deficient vitamin D level is, after a review of research on vitamin D, the Institute of Medicine reported that the vast majority of people have sufficient vitamin D levels when the 25(OH)D level (this is a simple blood test) is greater than or equal to 20 ng/mL. The people most at risk for vitamin D deficiency are those with a level less than 12 ng/mL.

Supplementing with vitamin D, though, overall is complex, as a person's individual level, and how much they may require daily to maintain a normal vitamin D level depends on a number of factors. These factors include:

• Skin color
• Average sun exposure
• Diet
• Whether a person has any medical problems (for example, liver or kidney disease).

In addition, it is possible to overdose on vitamin D, with the main side effect being high circulating blood calcium (hypercalcemia), which can lead to nausea, vomiting, and muscle weakness, and increase the risk of developing calcium kidney stones. Therefore, it is important to talk with your healthcare provider before taking any vitamin D supplements.

Also, while tanning beds and excessive sun exposure are not recommended for obtaining adequate vitamin D due to the risk of skin cancer, some experts suggest that small amounts of sun exposure such as 5 to 30 minutes daily or twice a week may be fine. That said, its best to proceed with caution and try to limit sun exposure to the skin whenever possible.