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Boston 2002 Friday, 15 February, 2002, 20:53 GMT
Sunshine 'prevents cancer'
AAAS Boston 2002, BBC

A small amount of sunshine can help reduce the risk of breast, colon and prostate cancers, according to US scientists.

Sunlight is a key source of vitamin D, and scientists told the American Association for the Advancement of Science annual meeting in Boston the vitamin plays a crucial role in regulating the production of cells, a mechanism which is absent in cancer.

The suggestion that we should get out in the sun may at first seem at odds with the advice on guarding against the risk of skin cancer, but Professor Michael Holick, an endocrinologist from the Boston University School of Medicine, stressed that he was advocating moderation, and not denying the harmful effects of sunburn.

To get the vitamin D from the sun, but protect against skin cancer, he suggests Caucasians spend five to 10 minutes in the sun, unprotected, two to three times a week. Sun creams should then be used if people spend any further time in the sun.

Key chemical

People with darker skins need to spend longer in the sun to get the necessary amount of vitamin D; the pigmentation in their skins blocks UV absorption.

The sun gives out ultraviolet (UV) radiation. The benefits come from the UV B type.

Professor Holick believes his research could explain why people living in colder, northern climates who get less vitamin D from the sun have a higher risk of dying from colon, breast and prostate cancers.

He said more people than might be expected were vitamin D deficient. In Boston, he estimated 40 to 50% of adults over 50 were vitamin D deficient.

Professor Holick's team has isolated a key enzyme, or body chemical, which is involved in the processing of vitamin D. It was found in the colon. He said if the body did not take in enough vitamin D then the enzyme would not be activated and the body would not be able to turn the vitamin into a form it could use.

The active form of vitamin D prevents colon cells from proliferating and prompts them to change into more mature cells which are less capable of becoming cancerous.

North and South

The Boston researchers have found the same process occurs in breast, skin and prostate cells.

Professor Holick said: "The most beneficial effect of exposure to sunlight is vitamin D protection. Moderation is really the answer. We were born and evolved in sunlight and so sunlight is probably important for good health."

Dr William Grant, an independent researcher from Virginia, has examined the difference in cancer rates dependent on where people live.

Dr Grant's US work, using data from the Atlas of Cancer Mortality, found death rates for breast, colon and ovarian cancers in Boston and New England were almost twice as high as they were in the southwest from 1950 to 1994.

He found the same link, with varying increased risk, for 13 cancers including bladder, kidney, stomach and non-Hodgkin's lymphoma.

He estimates there have been 23,000 deaths from cancer per year - taking the difference in UV radiation between northern and southern states - which could have been prevented if people had had enough vitamin D. He suggests this year, the figure could be 30,000.

Based on his US findings, he estimates a quarter of breast cancer deaths in the UK are as a result of vitamin D deficiency.

He told BBC News Online: "I believe my research should be considered a clarion call for more investigation by the health establishment on the benefits of solar radiation and UV B."

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Prof Michael Holick
It very much depends on the time of year and the latitude
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