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My blog continues this week on the subject of immune optimisation, and discusses the crucial role of Vitamin D and immune status.
Vitamin D : Delving Deeper
Traditionally, Vitamin D has always been associated with bone health due to its ability to increase dietary calcium absorption in the intestines and its consequent promotion of bone mineral density. However, since the mid-1990s, science has unveiled Vitamin D’s diverse and multiple effects on a whole host of body cells and systems which marks this out as a remarkable nutrient.
Vitamin D’s potent influence on immunity is increasingly being understood, although scientists believe they are only scraping the surface of their understanding of its huge impact on immune regulation. Every human immune cell has what is called a Vitamin D Receptor (VDR) which means each and every immune cell in our body is directly influenced by the “instructions” which Vitamin D expresses. However, before I expand on what this actually means in terms of immune function, let’s take a quick look at how we obtain Vitamin D through dietary and lifestyle practices.
Vitamin D: The Sources
Vitamin D can be produced both naturally in human skin cells, and obtained through dietary ingestion.
Vitamin D is synthesised in human skin cells by the action of UVB light from the sun’s rays. The skin reacts to UVB exposure by converting a form of cholesterol resident in our skin cells to an inactive form of vitamin D. This inactive form then travels in our bloodstream firstly to the liver, and then to the kidneys where it undergoes certain metabolic processes to produce the active form of Vitamin D.
Unfortunately, due to the widespread use of sunscreens and sun avoidance, this form of natural synthesis is very much underused. The UK’s distance from the equator also contributes to an increasing epidemic of Vitamin D deficiency which has resulted in UK government guidelines for Vitamin D supplementation for “at risk” groups including all pregnant and breastfeeding women, children from 6 months-5 years (excluding formula-fed infants), the over 65s (the efficiency of subcutaneous Vitamin D manufacture decreases with age), individuals with dark skin (dark skin makes less Vitamin D on exposure to sunlight) and adults who routinely cover up in the sun.
Safe sun exposure is suggested at anywhere between 5 and 30 minutes (depending on skin type) in direct sunlight on arms and legs until the skin turns very lightly pink. Undertaking this type of sun exposure three times per week between 11am and 2pm in spring, summer and autumn should provide sufficient Vitamin D stores to last through the winter months.
Vitamin D-rich Foods
In addition to subcutaneous manufacture, Vitamin D can be obtained through dietary intake, although sources are limited. Foods containing Vitamin D include oily fish (e.g. salmon, sardines, mackerel, herring), fortified dairy products, fortified breakfast cereals, fortified breads and eggs from grass-fed hens. Although cod liver oil is a good source of Vitamin D, it also contains high levels of Vitamin A which is an antagonist to Vitamin D and therefore decreases its bioavailability.
Vitamin D : Vitamin or Hormone?
The quick answer is both! The inactive form of Vitamin D is exactly that, a vitamin. But once metabolised to its active form in the liver and kidneys, it fulfils the definition of a hormone, in that “it is a chemical messenger released by a cell, gland or an organ (in the case of Vitamin D, the skin, our largest organ) in one part of the body which affects cells in other parts of the organism” (1) where it produces a physiological effect.
Vitamin D and Immune Regulation
Scientists first started investigating the effects of Vitamin D on upper respiratory tract infection (e.g. tonsillitis, laryngitis, sore throat, sinusitis, ear infections, the common cold) based on population-based observations that outbreaks of these infections tend to occur predominantly during months associated with lower sun exposure. Several reputable trials have since concluded a strong association between Vitamin D deficiency and increased risk of upper respiratory tract infection. Further studies conducted on Vitamin D-deficient subjects have revealed a strong correlation between reduced flu and cold infections and Vitamin D administration (2, 3, 4). The reason Vitamin D plays such a crucial role in this context is understood to be primarily due to its ability to increase the activity of T cells, which are a type of immune cell involved in attacking and destroying invading viruses and bacteria. As a result, Vitamin D-replete subjects display greater reactivity to invading bugs and are able to repel them with greater efficiency.
Furthermore, Vitamin D’s influence on T cell activity also plays a key role in its ability to modulate autoimmune disease (e.g. Rhematoid Arthritis, Multiple Sclerosis, Crohn’s Disease, Type 1 Diabetes). Again, scientists were first alerted to the effect of Vitamin D on autoimmune disease through population-based studies that revealed a higher incidence of autoimmune disorders in countries with increasing latitude (and hence less sun exposure). Autoimmune disease is characterised by the body’s own immune cells mistakenly attacking its own body cells believing them to be harmful invaders. Conversely to above, in the autoimmune context, Vitamin D acts to block the production of T cells involved in this self-destructive activity thereby diminishing the autoimmune response. It also decreases the number of another type of immune cell called the B cell which produces harmful chemicals which destroy native cells (5, 6).
Research into Vitamin D and its role in immune function is on-going but a strong association between Vitamin D deficiency and immune dysfunction is clear and individuals should seek to maximise their lifestyle and dietary exposure to Vitamin D sources to achieve optimum levels.
A Word of Caution
Before rushing out and stocking up on Vitamin D supplements, please seek advice from your GP or from a qualified Nutritionist. Excess levels of Vitamin D can also be harmful, so it is important to get your blood levels checked first to establish your current status, and supplement in an educated fashion. A qualified health practitioner will advise the type, quantity and timeframe of Vitamin D supplementation to establish optimum blood levels.
Juliet Schaffer from Evolve Nutrition is a fully qualified and accredited Nutritional Therapist with a Bachelor of Science degree in Nutritional Medicine. If you are seeking nutritional advice regarding a specific health concern, or would like guidance for achieving and maintaining a health-promoting diet, take the option of a free 20 minute telephone consultation to see how professional nutritional advice can benefit you. Check out Evolve Nutrition’s website at
www.evolve-nutrition.co.uk for contact details or phone 01279 726640 to book a free initial telephone consultation.
Juliet Schaffer, Nutritionist, Evolve Nutrition