The Northwest's dreary winters are infamous for inducing depression. But a growing body of evidence suggests it can raise your risk of cancer and increase susceptibility to other diseases, such as diabetes.

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The Northwest’s dreary winters are infamous for inducing depression. But being starved for sunlight can do more than kick you into a psychic hole.

A growing body of evidence suggests it can raise your risk of cancer, increase susceptibility to heart attack, diabetes and other disorders, and at least partly account for the region’s sky-high rates of multiple sclerosis.

The reason is vitamin D, an essential nutrient produced in abundance by skin exposed to the sun’s rays. Long dismissed as being important mainly for strong bones, the so-called sunshine vitamin is now recognized as a key player throughout the body, including the immune system.

Experts say vitamin D deficiency is much more common than previously believed — especially in northern climes like Washington, where solar radiation from October to March is too puny to maintain healthy levels.

“You’re in a dark, gloomy place,” said Bruce Hollis, a leading vitamin D researcher at the Medical University of South Carolina. “In the winter, you could stand outside naked for five hours and nothing is going to happen.”

Increased use of sunscreen has turned a seasonal shortfall into a year-round condition for many people. A recent survey in Britain found 87 percent of adults tested during winter, and more than 60 percent in summer, had subpar vitamin D levels. Doctors in many parts of the world — including California — report a resurgence of childhood rickets, soft bones caused by lack of vitamin D.

While supplements offer a cheap and easy solution, Hollis and other researchers argue the recommended intake is too low to provide many health benefits. A Canadian medical organization advises that pregnant and nursing women take 10 times the amount suggested in the U.S.

“You’re more likely to live longer and you’re less likely to die of serious chronic disease if you have adequate vitamin D on board,” said Dr. Michael Holick of Boston University School of Medicine, one of the world’s top experts. “It may well be the most important nutrient of the decade.”

Risks of low levels

When Lisa Hill went to her doctor complaining of joint pain, she was surprised to get a diagnosis of vitamin D deficiency. “I had never heard of it,” said the 54-year-old Gig Harbor woman.

Since leaving her native Southern California, her sun exposure has dropped dramatically.

“You’re like a little mole in a hole,” she said. “You just don’t get much sun here.”

Many doctors once scoffed at the notion of vitamin D deficiency, but testing has become more routine and is covered by most insurance.

University of Washington heart surgeon Dr. Donald Miller Jr. tested 78 of his patients and found three-quarters had “insufficient” levels of vitamin D.

“It was really pretty shocking,” said Miller.

In a study of 1,739 Boston-area residents reported last month, rates of heart attack, stroke and heart failure were about 50 percent higher in those with low levels of vitamin D.

In addition to strengthening bones, muscles and joints, high vitamin D levels have been linked with lower rates of colon, prostate, breast, esophageal and pancreatic cancer.

Harvard scientists found that high levels of vitamin D reduced children’s odds of developing asthma, while researchers in Pittsburgh reported that pregnant women with low vitamin D had greater risk of preeclampsia, a dangerous form of high blood pressure.

Vitamin D also appears to be one of the reasons multiple sclerosis and other autoimmune diseases are twice as common in northern vs. southern states. Washington’s rate of MS, which causes progressive nerve damage, is one of the highest in the nation.

Blood samples from more than 7 million military personnel showed people with the highest levels of vitamin D were 62 percent less likely to develop MS than those with the lowest concentrations. A study in Finland found similar results.

What D can do

Formed in skin cells exposed to UVB, the invisible form of light that causes sunburn, vitamin D and its breakdown products act throughout the body.

The compounds are believed to regulate as many as 1,000 genes, including genes that weed out precancerous cells and genes that slow the runaway reproduction typical of cancer.

Molecular geneticist John White and his colleagues at McGill University in Montreal discovered vitamin D also switches on an arm of the immune system that kills bacteria — including the bug responsible for tuberculosis.

“It’s a kind of front-line response to infection,” he said.

That may explain why TB patients in the early 1900s who basked in the sun at sanitariums were often cured, added White, author of a recent Scientific American article on vitamin D.

The compound has an anti-inflammatory effect, too, which probably plays a role in preventing heart disease and autoimmune disorders.

The evolutionary angle is also being explored, with the suggestion that early people who migrated north from the equator lost skin pigmentation to maximize vitamin D production. Today, dark-skinned people in northern latitudes are among the most vulnerable to vitamin D deficiency.

Inconclusive studies

While the evidence is piling up, most of it is still based only on association. Scientists count cancer cases, infer or measure vitamin intake, then look for correlations. Some researchers advise caution until there’s more data from controlled trials, where one group gets vitamin D, while another gets a placebo.

One such trial last year found 1,000 international units (IU) a day slashed cancer risk for women. But a much bigger study found women who took vitamin D supplements had the same risk of colon cancer as those who didn’t.

“I would say the jury is out,” said Ulrike Peters, who studies nutrition and cancer at the Fred Hutchinson Cancer Research Center.

Women in the large experiment took 400 IU a day of vitamin D — the amount in a typical multivitamin.

Hollis, the South Carolina researcher, says the results simply show that standard doses aren’t enough.

The U.S. Institute of Medicine (IOM) recommends 200 IU a day up to age 50, and 400 to 600 IU for older people. The Canadian Paediatric Society recently urged pregnant and nursing women to take 2,000 IU a day — which the IOM designates as the maximum safe dose.

Vitamin D experts say much higher doses are safe. Exposing just your arms and legs to the summer sun for less than 15 minutes can generate 5,000 IU, Holick pointed out.

It is possible to go overboard with supplements and trigger dangerous calcium deposits in kidneys and blood vessels, but Holick says it takes a lot: more than 10,000 IU a day for a year.

Milk and some cereals are fortified with small amounts of vitamin D to prevent rickets, but few foods are significant natural sources.

Tanning beds that produce UVB will generate vitamin D, though dermatologists go ballistic when Holick points that out. About 5 percent of his research funding has come from the indoor tanning industry, and he was fired from a joint appointment in Boston University’s dermatology department after authoring a book on the benefits of UV radiation.

Still, he continues to advocate “sensible” sun exposure that shields the face and stops far short of sunburn. He also recommends most people take 1,000 to 1,500 IU a day of vitamin D. Cholecalciferol, or D3, is the preferred form. Hollis takes 4,000 IU a day and recommends 2,000 IU daily for everyone.

Both continue to agitate for a change in official guidelines. But that would require a costly research review and isn’t likely to happen soon.

“Vitamin D is so cheap, nobody makes any money on it,” Hollis said. “So there’s nobody to push it.”

Sandi Doughton: 206-464-2491 or