Readers Digest June 2003 Cover Story
Reprinted from Reader's Digest, June 2003 edition.
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?
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 could 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.
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.
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.
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 bsence 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.)