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On Vitamin D

Recently in the Twitter-sphere, a question was posed: why should we stay out of the sun during the day when your body needs vitamin D? Many times we hear to get out in the sun to fill our vitamin D ‘quota’ while also hearing to avoid direct sunlight to avoid getting skin cancer. And there are many myths out there on where we can get vitamin D and how long we need to stay out in the sun to get it. So this week’s blog is (hopefully) an answer to all your Vitamin D and skin cancer related questions.

Early in evolution, vertebrates “depended on the cutaneous synthesis of vitamin D for increasing the efficiency of intestinal absorption of scarce sources of dietary calcium.”[1] Vitamin D is often called the ‘sunlight vitamin’ because it is produced in your skin when exposed to sunlight, but specifically UVB rays, making it more correctly a hormone than a vitamin. The body can also get vitamin D from food, but it is rare in the human diet. While sun exposure should be limited, that doesn’t mean vitamin D isn’t important. It is actually quite the opposite. Vitamin D promotes calcium absorption in the gut and it’s needed for bone growth and bone remodeling. Vitamin D also has other roles as well, “including modulation of cell growth, neuromuscular and immune function, and reduction of inflammation. Many genes encoding proteins that regulate cell proliferation, differentiation, and apoptosis are modulated in part by vitamin D.”[2]

Without sufficient vitamin D, bones can become thin and brittle. Vitamin D also protects older adults from getting osteoporosis. And vitamin D insufficiency has become an epidemic in adults over the age of 50 years all over the world. A growing body of evidence shows that vitamin D plays a crucial role in disease prevention and maintaining a healthy body. There are about 30,000 genes in your body, and vitamin D affects nearly 3,000 of them.[3] So, yes Vitamin D is very important.

But while the sun is a main source of vitamin D, the sun also poses a very large and apparent health risk and that is skin damage leading to skin cancer. So too much sun can lead to skin cancer and too little sun could lead to vitamin D deficiency leading to other diseases affecting your health. So what’s the answer? “There must be a balance between some sun exposure to produce vitamin D and the need for sun avoidance or protection to reduce risks of skin cancer.”[4]

While that may seem like an ambiguous answer, finding the balance could be key. But how much vitamin D do we need? Well, that answer isn’t black and white either. Your risk of vitamin D deficiency depends on a number of factors including latitude, altitude, time of day, season of the year, cloud cover, skin pigmentation, and clothing.[5] So determining the amount of Vitamin D you need can be on an individual scale. Some caucasians only need about twenty minutes of sunlight to achieve the right amount of vitamin D while in some areas of the world, you need 10 minutes or 2 hours. So to figure out where you fit, talk to your doctor and determine how much sun you need to maintain healthy levels of vitamin D while also avoiding overexposure to UV rays.

References:

[1] Michael F Holick, Sunlight Dilemma: risk of skin cancer or bone disease and muscle weakness, The Lancet, Volume 357, Issue 9249, 6 January 2001, Pages 4-6, ISSN 0140-6736.

[2] ibid.

[3] Dixon, K.M., Sequeira, V.B., Camp, A.J. and Mason, R.S., 2010. Vitamin D-fence. Photochemical & Photobiological Sciences 9, 564570.

[4] Watson, Ronald R. "Vitamin D and Melanoma." Handbook of Vitamin D in Human Health: Prevention, Treatment and Toxicity. N.p.: Wageningen Academic, n.d. 418-42.

[5] ibid.

Misha Kaura