Sunny lifestyles may halve prostate cancer risk
- From Newscientist:
* 05:00 15 June 2005
* NewScientist.com news service
* Anna Gosline
A healthy dose of daily sunshine could chop the risk of prostate
cancer in half, suggests the largest study so far on UV exposure,
vitamin D and prostate cancer risk.
"Up until now the only things we knew about prostate cancer were
things you can't change: being old, being black and living in northern
latitudes," says Gary Schwartz at Wake Forest University in
Winston-Salem, North Carolina, one of the research team.
Back in 1990, Schwartz noticed that people at a high risk of prostate
cancer were similar to people at risk for vitamin D deficiency: they
often lived in northern latitudes, had darker skin and were old.
Vitamin D is produced in the skin as a reaction to ultraviolet light
and it subsequently metabolised in the liver and kidneys to form
"active" vitamin D.
Since then, numerous studies have unearthed a link between sunny
lifestyles and reduced prostate cancer risk. But most researchers
either relied on broad geographical trends or on subjects recalling
specific memories of sun exposure. "The problem is that if you have
disease, your recollection of things that might have affected your
disease can be very biased," Schwartz explains.
Sun on their faces
So Schwartz, along with a team led by Esther John at the Northern
California Cancer Center in Union City, attempted to measure sun
exposure objectively. They measured skin pigmentation of 450 white men
with cases of advanced prostate cancer and compared them with 455
matched controls without the disease.
The team calculated the difference in skin darkness between each
person's forehead and their inner arm - an area that rarely sees
sunshine. Recent research has suggested that the increased forehead
pigmentation reflects a lifetime's worth of sun, darkening with age.
They found that men with the darkest forehead - in relation to their
inner arm - were 49% less likely to develop prostate cancer than those
with the smallest increases in forehead pigmentation. Furthermore, the
reduction in risk was even greater for those men who carried
particularly "active" forms of the vitamin D receptor (VDR).
Cheap and easy
Richard Strange at Keele University, UK, also researches connections
between prostate cancer and vitamin D. In a smaller group of British
white men, he and his colleagues found that higher occupational sun
exposure reduced risk. "Many of us now spend a very large part of our
lives indoors. We don't have high enough levels of vitamin D to
protect against certain cancers," he says. "The public health
potential is enormous. Vitamin D is cheap and easy, either as
supplements or as cautious exposure to UV. That's got to be good news."
But the benefits of UV on vitamin D levels must be balanced against
its known skin cancer risks, warns Cancer Research UK spokesperson
Henry Scowcroft. "For most people, it usually takes just a few minutes
of sun-exposure for your skin to make a very large amount of vitamin D
- much less time than it takes for the skin to burn or even redden.
But exactly how long is needed will depend on skin type, age, location
and time of day and year."
Schwartz advocates the use of dietary supplements, though optimal
doses are unknown. While future controlled trials may resolve dosage
issues, Schwartz suggests that men might as well increase vitamin D
supplements now. "In the US there are 240,000 new cases of prostate
cancer diagnosed each year. If you can do something that is safe and
inexpensive, why not?"
Journal Reference: Cancer Research (vol 65, p 5470)