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SOME
Sun is Good For You Remember
how good it used to feel, hanging out in the sun, letting your face
acquire that nice, ruddy glow? Then
came all those depressing public health messages telling us that the sun
was dangerous, that we should feel guilty about even the slightest tan. Well,
fellow sun worshipers, the sad truth is that as a general rule, we
should still practice “safe sun” - including hats and sunscreen,
especially for little kids - much of the time. But
there’s a new ray of hope - dare we say “sunshine?” - in the form
of a modest but significant shift in medical thinking toward the view
that SOME unprotected sun exposure may actually be a good thing, like 15
minutes or so a day in the summer for adult Bostonians who tan well,
less for those burn easily. ”In
my opinion,” says Dr. Robert Stern, chief of dermatology at Boston’s
Beth Israel Deaconess Medical Center, “it’s probably true that for
people over 40, even people who have had a non-melanoma skin cancer, we
have oversold the idea of having to be sun-phobic. For them, modest
exposure has little risk.” For
kids, cautions Stern, it’s another matter - excessive childhood
exposure to sunlight has been linked to later basal and squamous cell
skin cancers, as well as to melanoma, a more serious form of skin
cancer. The
rationale for the some-sun-is-good point of view, supported by a number
of recent articles in medical journals, is that the vitamin D made in
the skin in response to ultraviolet B radiation may protect against
certain diseases, including cancer of the breast, colon and prostate. Other
diseases, most notably MS (multiple sclerosis), also show a “latitude
effect,” that is, they are less prevalent among people in sunnier
climes, though, as with cancer, whether this is truly due to vitamin D
or to some other factor that varies by region such as diet, behavior or
genetics is unclear. In
rodents, high doses of vitamin D can actually prevent MS. Sunlight
may even be an effective treatment for some diseases. In a recent study
published in the journal Lancet, Dr. Michael F. Holick, an
endocrinologist and leading vitamin D researcher at Boston University
School of Medicine and others showed that exposing people with mildly
high blood pressure to UV-B can lower blood pressure, perhaps by
correcting an underlying vitamin D deficiency. Before
we get in too deep here, let’s be clear. It’s vitamin D that has the
real benefit, not sunlight per se, which means you can take vitamin D
supplements, especially during the winter if you live at higher
latitudes and especially if you have dark skin (which makes less vitamin
D). By contrast, people in Florida
typically make plenty of vitamin D all year in their skin. It’s
very tough to get enough vitamin D from your diet unless you consume
lots of fish liver oil, the flesh of fatty fish like salmon and
fortified milk and cereals. Actually,
vitamin D is not a vitamin at all in the normal sense, but is really a
steroid-like hormone made, after exposure to the UV-B rays from
sunlight, from a precursor
of cholesterol in the skin. After an inactive form of vitamin D is made
in the skin, it is transformed in the liver and kidney to the active or
hormonal form called 1,25 dihydroxy vitamin D. Indeed, several teams of
researchers have recently found that the organs such as the breast,
prostate and colon in which vitamin D seems to reduce cancer risk can
also make their own stores of the vitamin’s active form, an important
finding. Like
other hormones, vitamin D works by fitting into specialized receptors on
cells in many organs of the body and has numerous biological effects,
the most important one being to aid in the absorption of dietary
calcium. When a person has enough vitamin D in his system, the
intestines can absorb 30 percent of the calcium available in the diet;
without enough vitamin D, this drops to 10 percent, notes Holick. The
consequences of insufficient vitamin D can be serious. When the body
can’t absorb enough calcium from the diet, it steals calcium from the
bones to restore proper levels in the blood, a process that weakens
bones, often leading to osteoporosis. Low levels of vitamin D can also
lead to weak and achy muscles, as well as generalized bone pain,
symptoms often misdiagnosed as fibromyalgia. Just as important as its effects on calcium and bone is the fact that vitamin D helps regulate many basic cell processes, notes Dr. David Feldman, an endocrinologist and vitamin D researcher at Stanford University School of Medicine. By acting on specific regions of DNA called vitamin D response elements, it helps control the biochemical signals that tell cells when to divide, when to stop dividing and when to die - all processes that are crucial in both normal and malignant cells. Vitamin D as a supplement has also been shown to be extremely effective at preventing Type I diabetes. A study by Finnish researchers published in Lancet last fall shows that vitamin D (2000 International Units a day) in infancy can reduce by 80 percent the risk of Type I diabetes 30 years later, perhaps because vitamin D slows the body’s immune attack on its own insulin-producing cells. This fits with data from mice showing that high doses of activated vitamin D will markedly reduce the risk of Type I diabetes. But perhaps the most intriguing evidence of vitamin D’s importance comes from studies of sun exposure and cancer. In the March 15 issue of Cancer,
William Grant, by day an atmospheric scientist at NASA’s Langley
Research Center in Hampton, VA and by night, an independent researcher,
published a study showing that the geographic distribution of many
cancers varies with UV-B exposure. Since the early 1980s, Grant notes, scientists have been gathering evidence that some types of cancer - most notably, cancer of the breast, colon, ovary and prostate, as well as non-Hodgkin’s lymphoma - are higher in Americans who live in the least sunny regions. ”What
I did was basically take two maps and put them together,” says Grant
of his latest study. This showed that in addition to the cancers already
known to vary with UV-B exposure, there appear to be many others
(bladder, esophagus, kidney, rectum, stomach and uterus) that also
increase as sunlight decreases. In
fact, more than 30,000 Americans die prematurely every year from cancer
that may be attributed to low levels of UV-B exposure, Grant estimates. Other
researchers, too, have found links between sun exposure and cancer.
In 1999, a team led by epidemiologist Esther M. John of the
Northern California Cancer Center in Union City reported on a study of
more than 5000 white women, 190 of whom developed breast between the
time they were first interviewed by government researchers in the early
1970s and 1992. The
team correlated various measures of sun exposure and found that the
women with the highest levels of sun exposure were the least likely to
get breast cancer. This
March, researchers from the National Cancer Institute led by Dr. Michal
Freedman, an epidemiologist, found that Americans living in sunny areas
were significantly less like to die from (not just get) cancers of the
breast, ovary, prostate and colon. Not surprisingly, her team found,
high levels of sun exposure were also linked to the milder
(non-melanoma) types of skin cancer, too. The
bottom line ? If you’re white, all it takes for your skin to make
enough vitamin D is about 15 minutes a day in the sun, without
sunscreen, at noon, says Holick. If
you’re black, it may take considerably more than that. How much sun
you should get depends on your skin type and sensitivity to sun – if
you burn readily, you may only be able to tolerate five minutes in the
sun, and that would be enough. And
if you’d rather just take vitamin D supplements? That’s fine – the
general guidelines are 200 IUs a day if you’re 50 or under, 400 if
you’re between 50 and 70, and 600 IUs if you’re over 70, says Tufts
University epidemiologist Susan Harris. Some researchers even recommend
800 to 1000 IUs a day. (Since there’s almost no vitamin D in breast
milk, Harris notes, breast fed babies living in less sunny regions of
the country should probably take baby vitamins. The
risks of overdosing are small, adds Reinhold Vieth, a biochemist and
vitamin D researcher at Mount Sinai Hospital in Toronto, who believes it
would take tens of thousands of IU s for long periods to become a
problem.. Still, to be on the safe side, many researchers suggest
limiting vitamin D intake to 2000 IUs a day. Judy
Foreman is Lecturer on
Medicine at Harvard Medical School and an affiliated
scholar at the
Women’s Studies Research Center at
Brandeis University.. Her column appears every other week. Past columns
are available on www.myhealthsense.com. SIDEBAR Vitamin
D and the Evolution of Skin Colors
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