There is very poor evidence that vitamin D supplements reduce the harm from having a low blood level of vitamin D (“Sunbathing, sunscreen and vitamin D”, May 10). This raises the question whether there are other benefits from sun exposure that aren’t detected from the vitamin D blood test. Dermatologists from Edinburgh showed that one reason why vitamin D supplements did not reduce blood pressure but sunshine did was that the skin exposed to UV also produced nitric oxide, a substance that is well known to reduce blood pressure. There could of course be other unknown benefits of sunshine.
Cancer Research UK is too cautious in recommending a few minutes a day without sun protection — white skin needs from 30 to 45 minutes before maximum vitamin D production is achieved and then turned off. It also forgets about DNA repair enzymes (the chief reason why even the worst known human carcinogen, ie, tobacco smoke, takes 40-50 years to cause cancer). Most of us, despite living all our life exposed to a multitude of carcinogens, don’t get cancer.
For more than 30 years radiotherapists have known that 90 per cent of DNA damage caused by a single dose of radiation is repaired within two hours. This is the basis of how they safely fractionate treatment to cure cancer and not cause more harm than good. I do not believe CRUK has the evidence to say it is not the same for UV and as a result I think it has probably been doing more harm than good for the past 20 years.
Professor Emeritus in Medical Oncology, QMUL
I was resting on a camping-bed this morning in the sunshine for 45 minutes ..