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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 ultraviolet radiation. In southern latitudes, there is a selection for black skins able to prevent up to 95% of the incident 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 country such as the UK. My client list comprises a diverse 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 meaning 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 produced 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. Therefore measuring the total 25(OH)D level is the best test to assess levels of vitamin D (Kurt A. Kennel).
I routinely 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.
Deficiency 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.