Friday, April 8, 2011

Sun UV to trigger Vitamin D and skin cancer: intensity matters?

I've never read a report about this but I have had this suspicion for a long time. On the one hand, we need to expose our skin to the sunlight, preferably on a daily basis, in order to let the body synthesize enough vitamin D. On the other, we don't want so much exposure as to cause skin cancer. All reports or articles I know simply advise moderation in exposure time. But I have a hypothesis that intensity, or rather, local intensity multipled by time of exposure, matters more. Suppose the UV light coming to your skin is x lux's in intensity and it lasts y seconds. The chance of you getting skin cancer on that spot is proportional to x*y. If this hypothesis is true, then we have a good strategy to achieve both goals at the same time, getting enough UV and avoiding skin cancer: alternate the part of your body exposed to the sun, and never let the sun light come to one small part of the skin for an extended period of time.

Also see

Is there too much radiation from X-ray exams?


Yong Huang said...

Vitamin D's benefit is even expanded to human reproduction: Vitamin D is positively associated with sperm motility and increases intracellular calcium in human spermatozoa

S. Kiihne said...

Yes, you're right! I've been researching this for a while. My current approach is: maximize cover on face and hands as they are usually exposed. Minimize clothes for about 10 min around noon to get vitamin D. Both vitamin synthesis rates and DNA damage rates (i.e. skin cancer risk) depend on the duration of exposure and the intensity. There's no good public health message because intensity varies sooo much: latitude, ozone, clouds, season. And then there's skin color. The darker your natural (untanned) skin color, the slower the rates.

Yong Huang said...

Thanks for the comment. If you're a researcher, I'd love to know if there's scientific study on this, i.e. given the same total exposure, it's better to scatter it around your body than to focus on a small part.

Your comment on the skin color is good. I think I read articles on that before. Need to dig them out.