| The Healing Vitamin Are you getting enough?
Wilson Riley didn't know what ailed his baby
son, but by the time the boy was one, Riley was sure something
wasn't right. "His head was growing, but his body was really small,"
Riley recalls. At Boston Medical Center, the doctor told him his son
Kuool had rickets - a bone-bending disease caused by vitamin D
deficiency.
Looking back a century and more, the slums of
Boston, New York, and London teemed with children whose weak,
spindly limbs and bowed legs testified to their vitamin D
deficiency. (Tiny Tim, the character in Dickens's novel A Christmas
Carol, was a likely case.) The disease all but disappeared after the
1920's, when doctors realized it could be cured by sun exposure, and
farmers began fortifying milk with vitamin D.
But lately the malady has been making a comeback.
That's bad, and not just for kids, according to Boston University
medical school professor Michael Holick, who's spend the last 30
years researching the subject. He believes we're living amid an
unrecognized epidemic of vitamin D deficiency. And nowadays,
scientists are linking low levels of D to cancer, hypertension,
diabetes and osteoporosis. "More and more evidence is mounting that
vitamin D plays an absolutely pivotal role in all aspects of human
health," says Holick.
That's a major shift. Researchers used to think
D's main value was in building strong bones. But new research shows
that this humble nutrient is far more versatile. Unlike other
vitamins, D isn't found in much we eat - aside from fortified milk
and cold-water fish like mackerel and salmon. Instead, most is
supplied by the sun. A D-related hormone in the skin soaks up
the ultraviolet rays in sunlight and travels to the liver and the
kidneys, where it picks up extra molecules of oxygen and hydrogen.
This process transforms the "pre-vitamin" D into a potent hormone
called calcitriol. Part of the evolving understanding of this
nutrient is that scientists now think many tissues in the body - not
just the liver and kidneys - can convert the pre-vitamin D to make
their own disease-fighting calcitriol.
Let the sun bake your unprotected arms and face
for few minutes, and you'll make all the D you need - it sounds
simple, though a touch sinful. But combine our indoor lifestyle,
sun-blocking pollution, and the fact that even sunscreen with an SPF
of 8 reduces D absorption to virtually nil, and many of us end up
falling short, says Holick. Deficiency seems to be rampant among
Americans living above the 40th parallel - line that cuts from
Philadelphia to Columbus, Ohio, past Denver and through Northern
California. Sunshine is so scarce during Boston winters, Holick
says, that "you could stand outside naked from the time the sun
rises till it sets and you won't make any D."
Without sunlight, the body will run through
its reserves of the vitamin within a few weeks. In studies of
people living in the Northeast, anywhere from 20 to 60 percent of
those over age 50 are low on D. The elderly tend to be at higher
risk because their D-making machinery is less efficient.
Also, at elevated risk are African Americans,
since having darker skin makes absorbing UV rays harder. Doctors at
the Centers for Disease Control and Prevention recently found the 42
percent of African American women of childbearing age were
deficient.
One startling result of the growing D deficiency
is more and more rickets cases each year. Doting parents are doing
exactly what they should: breast-feeding their infants and keeping
them out of the sun. For much of his first year, Kuool Riley was
nursed - not much D there. (Experts recommend that breast-feeding
mothers should consult their pediatrician about D supplements.) And
the skies over Boston were generally overcast. "When we took him
outside, that little bit of sun clearly wasn't enough to do
anything," recalls his father, Wilson Riley. After doses of vitamin
D and various other therapies, the boy is now a healthy
kindergartner.
But what really worries Holick and others is what
Kuool's deficiency may represent: huge chunks of the world's
population living with a chronic lack of D that boosts the risk of
serious illnesses. At the top of the list?
Cancer
The cancer theory got its legs in 1980 after
Frank and Cedric Garland, epidemiologists who are also brothers,
were struck by maps showing that the rate of colon cancer was about
twice as high in the cloudy Northeast as in the Sunbelt. The pattern
not have been clearer, recalls Cedric Garland, now a professor at
the University of California, San Diego. Blue zones indicated low
rates of cancer, and red, yellow and white represented average to
above average rates, explains Garland. "South of the Mason-Dixon
line was all blue, and everything above it was red, yellow and
white." The Garlands were the first to suggest that differing D
levels might account for the phenomenon. Later studies supported
their hunch: People who consumed the most vitamin D or had the
highest levels of D in their blood had a lower risk of colon cancer.
Researchers are also probing links between prostate, breast and
ovarian cancers and a lack of sunshine and D. Indeed, scientists at
the National Cancer Institute recently surveyed death certificates
in 24 states and found the chances of dying from any of those
cancers was reduced by 10 to 27 percent for people in the sunniest
areas.
The idea makes sense biologically, explains Gary
Schwartz, and epidemiologist at Wake Forest University School of
Medicine who has studied the role of D in prostate cancer. Prostate
cells, he has shown, produce the hormone calcitriol, which can act
as a brake on cell growth. When the cells can't get enough of
vitamin D's precursor to make calcitriol, it's as if the brake lines
are cut. The cells can multiply uncontrollably, and cancer results.
Other experts are not yet convinced. "It's a
reasonable hypothesis, but not all studies show an association
between sunshine, D and cancer," says Donald L. Trump, chairman of
the department of medicine at Roswell Park Cancer Institute in
Buffalo. "The epidemiology is very suggestive," says Marji
Mccullough of the American Cancer Society. But, she adds, lack of
sunshine and D aren't the only explanations for the geography of
cancer. "People may have other risk factors."
Still, Gary Schwartz is convinced enough by the
data that he is not only administering but also participating in a
study in which healthy men are taking high doses of vitamin D to see
if it prevents prostate cancer.
Diabetes
In Finland, where the sun shows its face for only
a few hours a day during the winter, the natives have the world's
highest incidence of Type 1 diabetes. But Scandinavian researchers
there have found that giving infants, or even pregnant women,
vitamin D reduces risk for the disease. In one study tracking 10,000
children, researchers found that those who got regular doses of
vitamin D as infants were about 80 percent less likely to later
develop Type 1 diabetes than those who did not get enough. Animal
studies offer support: Mice bred to develop diabetes are far less
likely to get it if they are given vitamin D from birth. It's not
clear how D does the job. But Holick and others point out that Type
1 diabetes is an autoimmune disease. In research, D can suppress
certain immune cells, so the vitamin may help by preventing
destruction of the cells that produce insulin.
Hypertension
It's long been known that a population's average
blood pressure rises the farther the country is from the equator.
That's not just a matter of the laid-back tropics versus the urban
grind, according Holick. He recruited 18 volunteers with mild
hypertension and put them under UVB lights for at least six minutes
three times a week. After six weeks, the amount of D in their
systems had more than doubled and their blood pressure had dropped
significantly - to normal for some. The lights may work, says Holick,
because they boost calcitriol production by the kidneys, and
calcitriol tamps down enzymes that cause blood vessels to constrict,
a major cause of high blood pressure.
Osteoporosis
At conferences, Holick likes to make his point
about the importance of D to the bones by showing pictures of his
daughter's pet iguana. Without regular doses of UVB rays, the
lizard's bones start to break down. We're not any different, says
Holick. In the intricate ballad of calcium regulation, when D goes
missing, another hormone, parathyroid hormone, builds up and starts
pulling calcium out of the skeleton.
One result is the bone-brittling disease osteoporosis. Holick
believes the high rates of osteoporosis among the elderly can be
partly traced to the fact that many spend little time outside and
they're diligent sunscreen wearers. Indeed, studies suggest that 30
to 40 percent of American and British elders with hip fractures were
low on D. The problem could be remedied with the same ultraviolet
lights that iguana owners use for their pets. "We don't do this for
nursing home residents," Holick says, "but we'll spend 40 bucks for
lights for an iguana."
How Much D?
The dangers of not getting enough vitamin D
are so great that experts say people should take a blood test for D
levels once a year - just as they check their cholesterol regularly.
Current daily recommendations for vitamin D
suggest people under the age of 50 get 200 IUs a day; 51- to 60-
year-olds aim for 400 IUs; for those 70 and over, 600 IUs. That's
enough to keep bones healthy, but Holick and others believe we need
even more to avoid other diseases. In the absence of sunlight, the
daily dose may be more on the order of 800 IUs to 1000 IUs a day.
(More than 2000 IUs can be harmful, producing a toxic buildup of
calcium in the bloodstream.)
But getting 800 IUs isn't too hard to achieve. An
8-ounce cup of milk contains almost 100 IUs. For the lactose
intolerant or those who don't like dairy, Minute Maid offers
D-fortified orange juice. D supplements are easy to find, usually
packaged with calcium.
Better still, get outside. All it takes is
10-20 minutes a day - without sunscreen. |
