Wednesday, July 31, 2002 - 12:01 p.m. Pacific
By Scott McCredie
Seattle Times staff reporter
As the summer sun arcs high and languid across the Northwest sky, it's hard for visitors to fathom that for most of the year it puts in only cameo appearances.
From October through March its absence from center stage — specifically, its UV-B rays — may be contributing to what some experts are calling an "epidemic" of vitamin D deficiency here.
Estimates of the number of people at this latitude who are deficient in D range from 20 to 60 percent of the population.
So why should we people of the long winters care?
Among the elderly, osteoporosis (severe weakening of bones) is strongly tied to D deficiency.
And new evidence gathered in the past few years has found associations between vitamin D deficiency and illnesses such as cancer, heart disease, hypertension, diabetes and multiple sclerosis.
Since most results are preliminary, with no clinical trials completed, there's no need to push the panic button and rush to the drugstore for a bottle of cod liver oil (one of the richest food sources of vitamin D). But because vitamin supplements are inexpensive, sources of D are widely available, and plenty of good reasons exist to take it — such as improving bone health — experts say it makes sense to ensure that you're getting enough.
Vitamin D is created in the body when a narrow, invisible spectrum of sunlight, called ultraviolet-B, falls on skin.
The molecule goes through several changes as it travels from skin to blood to liver to kidney. Its primary job is to maintain normal levels of calcium in the blood — critical for bone health, and maintaining cells and connective tissue.
While long considered a vitamin, which is a class of essential nutrients that cannot be synthesized by the body, D is now commonly referred to as a hormone, something produced in one organ of the body, in this case skin, that acts on another (the intestine, where it regulates calcium). The distinction doesn't have a significant impact on health, but simply highlights the two different ways the body gets D, from food and from manufacturing it itself.
Some experts, including Reinhold Vieth, a biochemist who studies vitamin D at Mount Sinai Hospital in Toronto, Canada, contend that because humans originated in equatorial Africa, the substantially lower levels of vitamin D among modern humans who moved away from the equator may be causing a wide variety of physical problems.
Why we need D
With an adequate level of vitamin D in the blood, bone-mineral density increases and bone loss decreases, studies have shown. When D levels are low, children can acquire a debilitating bone condition called rickets.
Another well-known role of D is to lower fracture rates in the elderly.
"Hip fractures go up in the winter, and it's not because people go out and slip on the ice," explained Dr. Mary Laya, an internist in the Women's Health Care Center at the University of Washington who studies osteoporosis.
"People who are marginally vitamin D deficient become more so in the winter, and go out and break their hips."
Vieth and Dr. Michael Holick, a leading vitamin D researcher, have reported that vitamin D also improves muscle strength and balance, which may reduce the occurrence of falls that cause fractures.
What's going wrong?
Recent research has shed light on D's role in several other classes of disease.
In the 1980s, scientists plotted certain disease rates against latitude. They found an increased risk of dying of colon, breast, prostate and ovarian cancer in the U.S. as one traveled north of the equator. Other research found that the rate of multiple sclerosis, osteoporosis and hypertension also rise in a similar fashion.
Because sunlight, which is constant year-round at the equator but varies seasonally north and south of it, is the primary means by which most people get vitamin D, researchers suspect there's a relationship between levels of vitamin D and the occurrence of these illnesses.
Scientists are now studying how D might affect the mechanisms of cancer. While it has long been known that skin cells produce vitamin D, new studies have shown that prostate, colon and breast cells, and perhaps others, also have this ability. Holick says D's function is to be a "modulator of cellular growth, preventing cells from being too active." In other words, vitamin D is important for maintaining normal cell growth and possibly for preventing cancer.
Because the cancer hypothesis is new, many doctors have yet to even hear about it or have greeted it with skepticism.
"It's not very well studied at this point," said Dr. Beverly Green, associate director of preventive care at Group Health Cooperative in Seattle, who noted: "Nothing is really proven until randomized control trials are done. Sometimes there's just an association for a variety of reasons."
The National Institutes of Health says it is premature to advise anyone to take vitamin D supplements to prevent cancer.
Nor is there reason at this time to take D solely to improve heart health, though a new study lends support to the notion that D may play a critical role.
In April, at an American Heart Association scientific forum in Honolulu, researchers reported the results of an 11-year study of nearly 10,000 women over 65. Those who took vitamin D supplements had almost one-third less risk of dying from heart disease as women who did not take D.
Researchers suggest that D may prevent the buildup of calcium in the arteries that is associated with atherosclerosis, a clogging of the artery walls that causes heart disease.
Many scientists outside the realm of vitamin D research doubt the possibility that there could be widespread vitamin D deficiency. Dr. Alan Kristal, a cancer prevention researcher at Fred Hutchinson Cancer Research Center, and Dr. Alan Chait, who studies the cell biology of atherosclerosis at the University of Washington, both scoffed at the notion.
Yet osteoporosis researchers, among others, point to studies that show a large percentage of Americans have low levels of D.
"There's no question," said Holick. "Not only in the United States, but throughout North America and Europe."
Not surprisingly, skin-cancer specialists are some of the most vocal critics of vitamin D researchers who advocate getting out in the sun more, though the researchers say that because the human body is such an efficient manufacturer of D, people can get all the sun they need before burning occurs, in as little as 15 minutes.
What should you do?
"Sun prescriptions" for vitamin D would vary so much — by skin type, latitude, altitude, time of day and so forth — many health professionals instead favor vitamin supplements.
While most advise getting the U.S. government recommended "daily value" of vitamin D (200 IU — International Units — for adults between the ages of 19 and 50; 400 IU for those 51 to 69; and 600 for people over 70), those who study the hormone argue that more is necessary for optimum health, in the neighborhood of 800 to 1,000 IU daily.
"The current levels are enough to prevent rickets or osteomalacia (a bone condition), but not enough for your health," said Dr. Robert Heaney, a Creighton University endocrinologist who studies osteoporosis.
Heaney, who takes a 1,000 IU vitamin D supplement daily and drinks plenty of D-fortified milk, observed that the whole field of nutritional science is redefining itself, moving from disease prevention to "health optimization."
"(Vitamin D research) is a brand new field," he said, "so a lot of work has to be done. But there's a lot of promise in it."
Scott McCredie: 206-464-2430
Copyright © 2002 The Seattle Times Company