How much vitamin D do we need?
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Vitamin D is a fat-soluble vitamin that has several important functions in our body. Getting into the winter months, it may be time to think about adding a vitamin D supplement. Studies show that approximately 40-50% of North Americans and about 1 billion people worldwide are deficient in vitamin D.
Vitamin D is primarily made in the stratum basale layer of our skin when we are exposed to UVB sunlight (below I made a diagram of the steps involved in its production). We can get some from consuming liver, eggs, oily fish, mushrooms, and fortified milk but food is only a minor source compared to sun exposure or supplementation. Fat-soluble vitamins can be stored in our liver so there is a supply to draw on for a period of time. If you had about 10-20 minutes of sun exposure a few days per week during the summer, you likely have enough vitamin D in your liver to last until around Christmas time. So then we might want to consider supplementing with a little extra to ensure that we have optimal levels to get us through to spring.
In our skin, cholesterol is converted into Provitamin D3, then UVB sunlight converts that into previtamin D3 and then the heat from the sun on our skin converts that into vitamin D3. This is then transported through the bloodstream to the liver and it converted into 25-hydroxyvitamin D (this is the main circulating form that is detected in a blood test measuring serum vitamin D levels). The last step is the conversion of 25-hydroxyvitamin D into 1,25 dihydroxyvitamin D in the kidneys when stimulated by parathyroid hormone (PTH), also called calcitriol, and this is the active form that binds to vitamin D receptors in almost every cell of the body.
Tanning beds produce both UVA and UVB rays that have the wavelength required for the production of vitamin D and they may be a beneficial way to make Vitamin D because the entire skin surface can be exposed for a very short period of time to produce a significant amount of vitamin D. Having very short exposure times means that the risk of skin cancer is quite low but excessive exposure can cause skin cancer. Health Canada provides exposure time regulations for artificial tanning clinics to prevent people from exceeding time limits. 10-15 minutes in a tanning bed only once per week can produce 10,000 IU of vitamin D.
Vitamin D testing and treatment – a review of current evidence
Meta-Analyses of Vitamin D intake and colorectal cancer risk
Preventative effect of Vitamin D on seasonal influenza
Vitamin D and MS – MS Society of Canada
High serum vitamin D may protect against multiple sclerosis
Summary of research articles evaluating impact of Vitamin D
Vitamin D and depression – A systematic review
How much sun is equivalent to Vitamin D supplementation
Sunbeds can produce physiological levels of vitamin D
I am currently in the Philippines with about 30 degree weather every day. It’s amazing to take in the sun for about 20 minutes of my day, but I have noticed I get a white dot pigmentation often times during the summer? Have any ideas what that could be?
Thanks Wendi!
Wow, great weather! White dots can happen when your melanocytes (the cells in your skin that make the brown pigment when you tan) stop making melanin. It shouldn’t be a concern but if it increases then talk to a doctor to see if anything else might be going on 🙂