In just the past few weeks, researchers
have stated the following about vitamin D:
• Adults who consume 1,000
international units (IU) of vitamin D daily might lower
their risks of colon, breast and ovarian cancers by up
to 50%.
• Children whose mothers get
plenty of vitamin D during pregnancy have bigger, stronger
bones at age 9. In fact, maternal vitamin D matters more
than all the milk children drink in those first nine years.
Other studies suggest the vitamin
might even help prevent hypertension, diabetes and multiple
sclerosis.
"Everyone has always focused on bone
health, but that is only the tip of the iceberg," says
Michael Holick, a researcher at Boston University.
So would you benefit from more of
this vitamin?
|
Sources
of the 'sunshine vitamin'
|
| Only
a few common foods are good vitamin D
sources: |
| International
Units (IU) per serving |
| Cod
liver oil, 1 tablespoon |
1,360 |
| Salmon,
cooked, 3½ ounces |
360 |
| Mackerel,
cooked, 3½ ounces |
345 |
| Tuna
fish, canned in oil, 3 ounces |
200 |
| Sardines,
canned in oil, drained, 1¾ ounces |
250 |
| Milk
(non-fat, reduced-fat or whole), vitamin
D fortified, 1 cup |
98 |
| Margarine,
fortified, 1 tablespoon |
60 |
| Egg,
1 whole (vitamin D is found in egg yolk) |
20 |
| Liver,
beef, cooked, 3½ ounces |
15 |
| Cheese,
Swiss, 1 ounce |
12 |
Current
daily recommendation:
200 to 600 IU
Proposed by some:
1,000 IU
Source:
Office of Dietary Supplements, National
Institute of Health
|
|
|
Although there's some debate about
the various health claims — and even more about
how best to obtain the nutrient — many experts say
yes.
That's partly because many people
do not get even today's "adequate intakes" for bone health,
which are set by the Institute of Medicine: 200 IU daily
for children and young adults, 400 IU for those ages 51
to 70 and 600 IU for those 71 and older.
And 1,000 IU a day — the amount
Holick and some other proponents recommend? "Essentially
no one in the United States is getting that," he says.
Look at the food sources and it's
easy to see why. To get 1,000 IU a day, "you would have
to eat salmon every day, drink at least three glasses
of milk and a glass of vitamin-D-fortified orange juice,"
Holick says.
Not likely. So this is where the
controversial advice comes in. It turns out that you can
make your own vitamin D — by exposing your skin
to the sun. And Holick advocates just that: five to 10
minutes, two to three times a week from spring through
fall, without sunscreen, for people with average skin
tones; less for fair-skinned people and more for dark-skinned
people. (Dark skin takes more time to make the vitamin
— one reason many African-Americans are low on D).
Researchers speculate that differences
in sun-produced vitamin D partly account for different
cancer death rates among blacks and whites and among people
from different latitudes.
That idea is intriguing, but it's
no reason to sunbathe and increase your risk of skin cancer
and wrinkles, says Barbara Gilchrest, dermatology department
chairman at Boston University. In a review for an upcoming
edition of the Journal of the American Academy of Dermatology,
Gilchrest calls for more research on cancer prevention
and other claims. In the meantime, she says, anyone already
convinced can go ahead and take supplements. (Up to 2,000
IU is considered safe.)
Even Holick agrees that supplements
are often the only option in winter: "If you live above
Atlanta, Ga., you basically cannot make any vitamin D
from November through February; for New York and Boston,
it's mid-October through mid-March."
But he says taking enough is a hassle.
The typical multivitamin contains only 400 IU, he says,
so you need at least one vitamin D pill on top of that.
(Don't take two multivitamins because you will get harmful
levels of vitamin A, he warns.)
A small dose of sunshine, on the
other hand, is often readily available — and, he
says, pretty safe. That's where he parts company with
the dermatology mainstream, which says any unprotected
sun exposure adds to cumulative damage.
American Cancer Society senior epidemiologist
Marji McCullough says: "We'll definitely address this
issue in some way (soon). ... It's worth looking into."
