Vitamin D3: Best Time For Sun Exposure
Cutaneous malignant melanoma (CMM) is the most serious form of skin cancer, accounting for about three-quarters of all skin cancer deaths. New research now supports that avoiding the sun at mid-day will actually increase your cancer risk. This recommendation is based on work in England and Norway and the United States that the optimal time to be in the sun for vitamin D production is near to solar noon as possible - between 10:00am and 2:00 pm. There are 2 reasons for this:
1) You need a shorter exposure time near solar noon because the UVB is more intense.
2) When the sun goes down towards the horizon, the UVB is filtered out much more than the UVA. It’s the long wave of ultraviolet called UVA, which runs from about 320 to 400 nanometers, is highly correlated with melanoma -- whereas the UVB is the one that produces the vitamin D, and that’s from 290 to 315 nanometers. If you want to get out in the sun to maximize your vitamin D production, and minimize your risk of malignant melanoma, the middle of the day is the best time and safest time to go.
Squamous cell carcinoma is linked to lifetime ultraviolet B sun burning, whereas melanoma is linked to lifetime ultraviolet A sun burning. By telling people to put on sunscreen and avoid the mid-day sun, dermatologists were actually giving recommendations that may have led to increased melanoma. Both UVA and UVB can cause tanning and burning but UVA penetrates your skin more deeply than UVB, and is thought to be a much more important factor in photoaging, wrinkles and skin cancers.Getting about 2,000 IU to 4,000 IU a day of vitamin D can help you to reduce your cancer risk by up to 50 percent! About 30 percent of cancer deaths -- which amounts to 2 million worldwide and 200,000 in the United States -- could be prevented each year with higher levels of vitamin D. However, most people only get 250-300 IU a day from their diet, so another source -- ideally the sun -- is essential.
Another common myth, aside from that of avoiding the mid-day sun, is that occasional exposure of your face and hands to sunlight is "sufficient" for obtaining healthy vitamin D levels. For most of us, this is a miserably inadequate exposure to move vitamin levels to the healthy range. You need to expose large portions of your skin to the sun and you need to do it for more than a few minutes. In Caucasian skin, an equilibrium occurs within 20 minutes of ultraviolet exposure. It can take three to six times longer for people with dark skin to reach the equilibrium concentration of skin vitamin D.
So, bearing in mind that you need to gradually increase your time, starting in the spring, you should be aiming toward exposing large areas of your skin to the sun, anywhere from 20 minutes at a time to two hours at a time, depending on your skin type and environmental factors. Longer exposures will be needed if sunbathing occurs at off-peak times for ultraviolet light (before 12 noon or after 3 p.m.) or at the beginning or end of the summer (April or September).In the winter months, a vitamin D3 supplement (cholecalciferol), the type of vitamin D found naturally in foods like eggs, organ meats, animal fat and fish, can be used.
Source: Advanced Experiments in Medical Biology 2008; 624: 86-88
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