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28
Jul
2015

Vitamin D - The Sunshine Vitamin

Kim Pearson graduated from Institute for Optimum Nutrition in 2008 and has worked in the field of and health for over ten years.

We’re constantly warned of the damaging and ageing effect of the sun’s rays on our skin, but in avoiding sun exposure, could we be doing ourselves more harm than good?

Exposure to UVB radiation provides the mechanism for more than 90% of the vitamin D production in most individuals (Norval M, 2009) but wearing a sunscreen with an SPF as low as eight reduces the skin's production of vitamin D by an incredible 95% (Reichrath J, 2008).

Why Is D So Essential?

Despite its name, vitamin D is actually a prohormone and is essential for numerous functions throughout the body. It plays a key role in calcium making it integral to bone health. (DeLuca HF, 2004). It’s also for healthy neuromuscular, cardiovascular and immune function, respiratory system function and cognitive function (Christakos S, 2013). Vitamin D is also vitally important to skin health as it is directly involved the and differentiation of keratinocytes. If adequate amounts of vitamin D are not available, epidermal cells cannot differentiate optimally. (Matsumoto K, 1991)

Deficiency – It’s More Common Than We Think

Vitamin D deficiency is more common than previously believed. The Centers for Disease and Prevention reported that the percentage of American adults with sufficient vitamin D levels (defined by 25(OH) D of at least 75 nmol/L) declined significantly between 1994 – 2001. Between , 60% of Caucasian Americans has sufficient vitamin D levels, this dropped to approximately 30% in and from approximately 10% to 5% in African Americans during this same time (Kennel KA, 2010). This means that from , an 70% of Caucasian Americans and 90-95% of African Americans were estimated to have insufficient vitamin D levels.

For a long time, we have been aware of the impact of severe Vitamin D deficiency which manifests as rickets. Rickets is a childhood disease characterised by growth retardation, deformities of the legs, bending of the spine, knobby projections of the ribcage, and weak and toneless muscles (Holick MF, 2006). A disease of the 19th Century, rickets was virtually eradicated half a century ago as diets improved in postwar Britain, however, there has been a re-emergence of the in recent years. In January 2011 Dame Sally Davies, the government's chief medical officer, recommended all children aged six months to five should be given vitamin D supplements, especially during winter months when the opportunity for sun exposure is reduced. Advice for children to wear a high factor sunscreen and remain covered up while outdoors is partly felt to be behind the reason for the re-emergence of rickets (Lowdon J, 2011)

Aside from rickets, epidemiologic evidence links vitamin D deficiency to autoimmune disease, cancer, disease, depression, dementia, infectious diseases, musculoskeletal decline, and more (Haines ST, 2012). Common manifestations of vitamin D deficiency are symmetric lower back pain, muscle weakness, muscle aches, and throbbing bone pain elicited by pressure over the sternum or tibia (Bordelon P, 2009).

More subtle signs of vitamin D deficiency may include fatigue and increased susceptibility to infection however an individual may be completely asymptomatic and still be deficient.

In addition to reduced sun exposure, being pregnant or breastfeeding can increase the risk of Vitamin D deficiency, as can wearing very covering clothing and/or spending a lot of time indoors. Babies and young under the age of five and older people aged 65 years and over are also at increased risk.

Vitamin D and Skin Type

An interesting point to note is that the darker a person’s skin type, the lower their ability to synthesise Vitamin D. Vitamin D3 is produced in skin through ultraviolet irradiation of 7-dehydrocholesterol. It is biologically inert and must be metabolized to 25-hydroxyvitamin D3 in the liver and then to 1alpha,25-dihydroxyvitamin D3 in the kidney before function (DeLuca HF, 2004).

An extract from the journal Science in 1967 states: In northern latitudes, there is a selection for white skins that allow maximum photoactivation of 7-dehydrocholesterol into vitamin D at low intensities of radiation. In southern latitudes, there is a selection for black skins able to prevent up to 95% of the ultraviolet from reaching the deeper layers of the skin where vitamin D is synthesized. (Loomis WF, 1967)

In a modern world where migration is common, people whose skin type has adapted to prevent excess vitamin D synthesis in their native, sunny environment are particularly prone to a deficiency when living in a sun-deprived such as the UK. My client list comprises a ethnic background. Muslim women who cover themselves for religious reasons are often found to be Vitamin D deficient. My Asian clients with Fitzpatrick IV-V skin type are also commonly deficient. That said, I have also seen plenty of Fitzpatrick Type I clients with low, or borderline vitamin D levels. Most of us spend a significant proportion of our time indoors that regardless of skin type, anyone can be affected.

How Do We Assess Vitamin D Levels?

Vitamin D levels can be easily assessed using a simple blood test. Ingested and cutaneously vitamin D is quickly converted to 25(OH)D, but in serum, only a small fraction of 25(OH)D is converted to 1,25(OH)2D, its active metabolite. measuring the total 25(OH)D level is the best test to assess levels of vitamin D (Kurt A. Kennel).

I test my client’s 25(OH)D levels through The Doctor’s Laboratory (TDL) but a number of laboratories offer this service. It can be done independently or as part of a more comprehensive vitamin and mineral screen. When possible I prefer to run a comprehensive micronutrient panel and then retest the specific deficient nutrients at two to three months post supplementation.

is defined as a serum 25(OH)D level of less than 50 nmol per L. Insufficiency is defined as a serum 25(OH)D level of 50 to 75 nmol per L (Bordelon P, 2009). Of the last 20 clients that I have tested, six were deficient, six had suboptimal levels and just eight had optimal levels. Those with optimal levels were usually either supplementing or spent a significant amount of time abroad. Two of those who tested deficient had levels below 10nmol per L.

How Should We Supplement Vitamin D?

The dosing strategy for correcting vitamin D deficiency differs from that for most other nutrients. Normally we take a