June 17, 2003

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Sun

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Medicine
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PERSONAL
HEALTH

A Second Opinion on Sunshine: It Can Be Good Medicine After
All
By JANE E.
BRODY

an sunshine, now shunned by so many who fear skin cancer
and wrinkles, save many more lives than it harms? Most definitely,
says a leading expert in the field, Dr. Michael F. Holick, a
professor of medicine, dermatology, physiology and biophysics at the
Boston University School of Medicine.

Dr. Holick, who discovered the active form of vitamin D, has
pulled together an impressive body of evidence in support of his
advice that no one should be, as he puts it, a "sunphobe" or, for
that matter, a sun worshiper.

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He has concluded that relatively brief but unfettered exposure to
sunshine or its equivalent several times a week can help to ward off
a host of debilitating and sometimes deadly diseases, including
osteoporosis, hypertension, diabetes, multiple sclerosis, rheumatoid
arthritis, depression and cancers of the colon, prostate and
breast.

In other words, Dr. Holick says, sunshine is good medicine.

But like all medicines, the right dosage is critical to reaping
the rewards that sunlight has to offer without suffering unwanted
consequences.

Dr. Holick elaborates on these research-based ideas in a small
but important book, "The UV Advantage," written with Mark Jenkins, a
health writer. Though originally scheduled for publication next
month, the book fell victim to a publishing world shake-up and will
not come out until the fall or winter.

But given the arrival of the sunshine season, people should have
the opportunity to benefit from the doctor's insights without
further delay.

A Ubiquitous Hormone

Dr. Holick's argument that controlled exposure to sunshine can
have powerful health benefits stems from decades of research into
the many roles played by vitamin D in the body. The main source of
this essential nutrient is neither food nor dietary supplement. It
is sunshine.

Vitamin D is made in the skin when it is exposed to the
ultraviolet B (UVB) rays in sunshine, as well as those from tanning
machines. But the amount of vitamin D formed in a given period of
sun exposure depends on the color of that skin — that is, how rich
the skin is in melanin, which blocks UV rays.

The darker a person's skin, the longer he or she has to be in sun
to form a significant amount of vitamin D.

A national study showed that 42 percent of African-American women
ages 15 to 49 were deficient in vitamin D by the end of winter. A
very dark-skinned person may need to spend up to 50 times as much
time in the sun to make the same amount of vitamin D as someone of
Scandinavian descent. For the average African-American, 5 to 10
times as much time in the sun will be needed.

Another critical factor is where a person lives in relation to
the Equator. The farther away, the less intense one's exposure to
UVB rays. This is undoubtedly why people in northern latitudes
evolved with light skin, to enhance their ability to absorb UVB
rays, and those near the Equator evolved with very dark skin, to
limit that absorption to a physiologically desirable amount.

For vitamin D to perform its myriad biochemical roles in body
cells, it must first be converted into an activated form, vitamin D
hormone. For years it was thought that this process took place only
in the kidneys, which then sent tiny amounts of the hormone to the
circulatory system for delivery to other tissues.

But studies by Dr. Holick and others have shown that the cells in
many different organs do not have to rely on the meager supply of
vitamin D hormone from the kidneys. Rather, cells in other tissues,
including the prostate, breast, colon and immune system, are also
able to convert vitamin D into the active hormone.

Many Health Effects

Everyone should know that vitamin D is critical to the formation
and maintenance of normal bones. Even if people consume enough
calcium, they cannot build and maintain bone mass if they are
deficient in vitamin D. One symptom of vitamin D deficiency is pain
and weakness in the muscles and bones. Based on that symptom, Dr.
Holick has suggested that some disorders diagnosed as fibromyalgia
may in fact be vitamin D deficiency.

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