MMS Physician Focus: December 2009
By David C. Dodson, M.D.
Vitamin D has come a long way in a short time. When I was a
medical student in the 1970s, all that was known about this
nutrient was that it helped to absorb dietary calcium. It was
necessary for forming bones, and lack of the vitamin gave rise to
the bone diseases of rickets in children and osteomalacia in
adults. Both conditions cause bones to hurt, bend, and break.
We now know that every cell in our bodies contain receptors for
vitamin D and that vitamin D modifies the activity of about 10,000
genes, or about one third of the human genome. Vitamin D, it seems,
does an enormous amount of work in our bodies.
Once it was thought that vitamin C helped prevent everything
from the common cold to cancer. That notion was largely
eminence-based: the eminent Linus Pauling, winner of two
Nobel Prizes (chemistry in 1954, for discovering the molecular
structure of vitamin C; a peace prize in 1962) widely promoted this
idea.
Today in this era of evidence-based medicine, good
evidence supports the idea that vitamin D not only boosts the
immune system, helping to prevent colds and flu, but also helps
regulate blood pressure, blood sugar, protect from many of the most
common forms of cancer, and even possibly to help fight depression.
And it still helps to make bones and muscles stronger, probably
accounting for its proven role in helping prevent falls in the
elderly, an often devastating and sometimes deadly problem. Indeed,
a recent study showed that lower vitamin D levels are associated
with higher death rates in the elderly.
Many surveys have documented the high prevalence of vitamin D
deficiency in people who live in more northern locations and in
people with darker skin. Indeed, pale skin allows the body to make
more vitamin D when exposed to sunlight, the reason why vitamin D
is sometimes called the sunshine vitamin. Our skin makes vitamin D
when it's exposed to ultraviolet light from the sun.
Unfortunately, north of Atlanta, the ultraviolet light is
filtered out by the atmosphere during the winter, and, as a result,
vitamin D levels tend to drop as one heads north. The deficiency
increases in people with dark skin, which protects from the sun's
harmful effects such as wrinkles and skin cancer, but at the same
time reduces our skin's production of vitamin D.
Few foods naturally contain vitamin D, although it's added to
some foods including milk and some brands of orange juice. Other
sources include small fish eaten whole, such as anchovies and
sardines, and cod liver oil.
I'm a major advocate for vitamin D supplements. While moderate
sun exposure certainly can and does boost vitamin D levels, it does
so at the cost of aging the skin, which means not only wrinkles but
also the possibility of skin cancer. So while moderation in all
things may be a reasonable policy with regard to sun exposure, it's
easier and safer, especially at northern latitudes, to take a
vitamin D supplement. It costs pennies per day and is an excellent
investment in your health.
How much is enough? This should be determined in consultation
with your doctor, based upon your actual vitamin D level, which can
be measured by a simple blood test. Because vitamin D is fat
soluble, it builds up in our body's fat stores, and one can
overdose on it. But doses as high as 10,000 units daily have been
shown to be safe, and typical recommended doses range from roughly
1,000 to 4,000 units daily. So overdose is unlikely.
For pennies per day, this substance can help reduce falls and
fractures in the elderly, prevent colds and flu, help control blood
pressure and glucose levels (diabetes), and may help prevent some
of the most common forms of cancer such as lung, breast, colon, and
prostate. Also, African Americans suffer higher rates of such
illnesses as high blood pressure, cancer, and diabetes - all
conditions associated with vitamin D deficiency.
As vitamin D can help reduce the incidence and severity of many
conditions and disease, it could therefore help control health care
costs - a major national concern. With all of its potential
benefits, vitamin D is certainly worth a closer look. For more
information, read the American Public Health Association's policy
statement on vitamin D at www.apha.org.
David C. Dodson, M.D., a primary care physician with the
Marino Center for Integrative Health in Wellesley, Mass., is Chair
of the Committee on Men's Health and a member of the Committee on
Nutrition and Physical Activity of the Massachusetts Medical
Society. Physician Focus is a public service of the Massachusetts
Medical Society. Readers should use their own judgment when seeking
medical care and consult with their physician for treatment. Send
comments toPhysicianFocus@mms.org
