As you are probably aware, exposure to sunlight causes vitamin D₃ to be made in your skin. In fact, it's recommended that you get 15 - 20 minutes of sun exposure, with approximately 40% of your skin exposed, 3 or 4 times per week to make adequate vitamin D₃ levels.

But which type of sunlight is important? All the way through medical school and training, I was taught that everyone needs to have a sun blocker on their skin to help prevent skin cancers. Not all sunlight is dangerous. The portion of the solar spectrum which is important to make vitamin D is the UVB spectrum and this wavelength does not cause cancer. Malignant melanoma has been increasing at an exponential rate in indoor workers since before 1940. The reason for this is the fact that glass blocks the penetration of UVB light due to the shorter wavelength. Glass does not block UVA and it can pass through the glass.

UVA light is the light responsible for causing cancerous mutations. It can also break down the vitamin D₃ formed after outdoor UVB exposure. We also know that vitamin D₃ is a potent defense against melanoma as these cells convert it to calcitriol. Calcitriol inhibits melanoma cell growth and programmed cell death both in vitro and in vivo preparations. Recent studies have shown that melanoma is promoted when there are increased UVA exposure and inadequately maintained skin levels of vitamin D₃.

So what do we know about sunlight exposure and/or vitamin D?

• Sunlight has 2 ultraviolet types of light, UVA and UVB.
• UVA light promotes Malignant Melanoma cells to grow by causing oxidative stress and UVB light helps to inhibit growth and makes vitamin D₃ in our skin.
• 50% of adults and approximately 30% of children are deficient in vitamin D.
• UVA light destroys vitamin D production in our skin and promotes photo-aging of skin, while UVB makes vitamin D in our skin.
• Glass blocks the safe UVB waves from reaching us, but allows the passage of UVA rays because they are a longer wavelength and can penetrate ordinary glass.