New thinking on UV rays and vitamin D

This is where the controversy begins. conventional wisdom on UV exposure is being challenged in light of its contribution to vitamin D production.

Scientists across a range of specialties argue that small and controlled amounts of UV rays on unprotected skin for a very short time might be beneficial for both our general health and specifically, to make our skin stronger. And they hope that in the near future we’ll be able to control our sun exposure better, allowing just the right dose of UV light to come through.

Professor Newton-Bishop, Professor of Dermatology at Leeds University, conducted a study published in 2010 that showed how the relationship between sun exposure and risk is complex. For example, some studies have suggested that occupational sun exposure, like that which gardeners face, might actually be protective against melanoma. Continuous sun exposure (not associated with severe sunburn) can induce photoadaptation (i.e. increased melanisation and epidermal thickening) — a possible reason why sun exposure might actually protect against skin cancer.

[pull_quote align=”right” ]Scientists across a range of specialties argue that small and controlled amounts of UV rays on an unprotected skin for a very short time might be beneficial for both our general health and specifically, to make our skin stronger[/pull_quote]

Dr Frank R. de Gruijl, Associate Professor in Skin Research at the Leiden University Medical Center, says that if we completely shy away from the sun, the risks of sun allergy — known as polymorphic light eruption in medical terms — will increase; one out of three women with skin type I are reported as having a mild form of sun allergy, experiencing a rash several hours after sun exposure.

Indeed, we might be losing our own natural defence against sunlight. Melanin protects us from the sun by increasing our level of pigments, and the outer layer of our skin gets thicker when exposed to light. These natural processes could happen in the spring to prepare our skin for summer. In other words, in some cases sunlight in the right dose seems have a preventive effect for future photodamage, helping the skin protect itself from sun radiation.

When you expose your skin to sunlight with UVB, two things happen simultaneously: on the one hand, you get skin damage, and on the other, you make vitamin D. Dr Mason found that when you make vitamin D in the skin, it is converted to other vitamin D compounds, which might play a role in protecting skin from sun damage. She believes that the damage from sunlight is less than what would occur if you didn’t make vitamin D, and the sun damage would be worse if vitamin D and its metabolites, including those from over-irradiation products, were not formed in the skin.

Endocrinologist and Professor of Medicine and Dermatology Veterans Affairs Medical Center and University of California, San Francisco, Dr Daniel D. Bikle, has also found that vitamin D is photoprotective. It has been proven in mice that vitamin D receptors (VDR), which are available in many cells in the body, such as keratinocytes, can protect against skin cancer. However, it is yet to been proven in humans.

VDR in combination with 1,25-dihydroxyvitamin D (calcitriol) enhances the differentiation of keratinocytes and inhibits proliferation. On a daily basis, UVB causes mutation in the DNA. This is actually a very common and natural process, and the epidermis knows how to repair these mutations, but in the absence of epidermal vitamin D, DNA mutations are not getting repaired — permitting unregulated proliferation of these cells, which might result in skin cancer.

Is there such a thing as a safe sun exposure dose?

The question about the threshold of sun exposure — the healthy dose of UV per skin type before we start damaging our skin — hasn’t been properly studied as yet. Some experts such as Dr Bikle feel confident saying that a healthy dose of sun exposure could be measured at level one on the minimum erythema dose (MED) scale, which means avoiding any reddening of the skin. (For skin type one, level one means no sun exposure at all because the skin is so sensitive that it burns immediately.)