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Vitamin D is a Hormone Not a Vitamin

Roughly 80% of the immune system resides in the gut.

Read that again.


Everything we do and put into your bodies affects the immune system (you are what you eat, right?). Here I share with you why Vitamin D is hailed one of the most important hormones to help strengthen and build a stronger immune system.

Did you know that Vitamin D is actually a hormone rather than a vitamin? In fact, the final product of Vitamin D conversion in the body is considered a hormone. We can obtain Vitamin D from some foods such as oily fish, egg yolks, mushrooms, fortified foods and soy, however 90% of the Vitamin D we get is made by our bodies. The body makes Vitamin D from direct sunlight (particularly UVB radiation) in the skin and the synthesis process continues in the liver and kidneys, until producing the final active form of the hormone.

Several different types of cells in the body, including immune cells, contain the receptor for Vitamin D, which means they can respond to Vitamin D molecules, triggering different reactions in the body. No wonder Vitamin D can affect so many aspects of health including bone health, cardiovascular health, immunity, autoimmune disease, type I diabetes, and mental health.

But because the cold season is upon us, I am here to share with you how Vitamin D affects the immune system by helping to keep that undesired cold at bay.

Can Vitamin D Help With Colds and Flu?

Absolutely! There is tonnes of scientific research backing up that a deficiency in Vitamin D increases the chances of infection.

A study has shown that individuals with low Vitamin D levels are more likely to develop upper respiratory tract infections than those with sufficient levels. And several studies have reported an association of lower Vitamin D levels and increased rates of infection, including influenza.

Find the study here.

How Does Vitamin D Support The Immune System?

The role of Vitamin D in the immune system has been recognised for about 35 years, however it was only in recent years that the implications of Vitamin D deficiency on the immune system have become clearer.

There are two types of immune system, equally important in fighting infections, the innate system (responsible for quickly fighting infections) and the adaptive system (which produces a slower response but is highly specialised, e.g. responsible for the production of antibodies).

Vitamin D seems to modulate both systems which explains why this hormone has such a wide effect on the immune system. In fact, Vitamin D is also known to play a role in autoimmunity. A prevalence of Vitamin D deficiency is observed in people with autoimmune disease, including multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease and lupus erythematosus.

How Can I Boost My Levels of Vitamin D?

Regular exposure to sunlight is the most natural and desirable way to get enough Vitamin D. In the UK sun, aiming for 10-20 minutes of exposure around midday several times a week is usually a good balance between adequate Vitamin D levels and avoiding the risk of skin cancer. During the spring and summer months we are more likely to cover our daily needs of Vitamin D from sunlight exposure.

Vitamin D is stored in the body for approximately 2 months. Therefore, the Vitamin D you stocked up during your much-loved sunny days back in the summer will start going away as the shorter and colder days of winter get closer. Since it is difficult to get enough Vitamin D from food alone, the best way to cover your daily requirements in the winter months is to take a supplement.

Supplements mainly come in two forms, Vitamin D3 or D2, with D3 being more efficient at raising Vitamin D levels in the body. Vitamin D3 is best taken in supplement form. My high dose formula of 3000IU helps to build up a stronger immune system, fight off colds and flu within the cooler months, plays an integral role in skin rejuvenation and protection and helps to destroy free radicals that can cause premature ageing. Check it out!

A balanced gut is also key to a healthy immune system – read about gut balancing foods here.


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