The vitamin D craze has been building over the last few years, with low levels of the supplement being the blamed as a source of many of our ills. Depression? D can ease it. Chronic pain? Take D. It is said to prevent kidney disease, diabetes, osteoporosis, colon and breast cancer, cardiovascular disease, or even the common cold. Recently, a study linked low vitamin D levels to the rise in Caesarean births.
Some studies, mainly epidemiological research that hunts for associations between diseases and possible causes, would seem to support that enthusiasm. For example, Cedric Garland, professor of family and preventive medicine at the University of California San Diego School of Medicine and colleagues, found that “the serum level associated with a 50 percent reduction in risk [for colon cancer] could be maintained by taking 2,000 international units of vitamin D3 daily.” Garland believes the good news is being suppressed.
“We are curing cancer and diabetes and nobody is doing anything about it,” Garland said.
Well, not quite. Partly through the agitation of evangelists like Garland, along with the efforts of the indoor tanning industry, the vitamin companies, and medical testing outfits, the message has been heard. Patients are now getting their vitamin D status tested at such a rate Quest Diagnostics, the world’s largest medical testing company, reports double digit sales growth of vitamin D tests, which can cost upwards of $200.
How much is enough?
Meanwhile, skeptics doubt many of the health claims and question the need and even the validity of widespread testing. They recall how large doses of vitamins C and E were supposed to prevent cardiovascular disease. Beta-carotene was supposed to prevent lung cancer. Selenium kept prostate cancer at bay. None of it turned out to be true, and some of the advice even proved harmful.
Vitamin D was discovered 87 years ago by team of scientists at Johns Hopkins University who cured mice with rickets by feeding them cod liver oil. Oily fish like sardines remain one of the few natural food sources of vitamin D.
It was later found that certain wavelengths of ultraviolet light prompt our bodies to synthesize vitamin D, eventually making a hormone called calcitriol that, among other things, controls how the body uses calcium and mineralizes bone.
Once this was understood, vitamin D was produced synthetically and foods, mainly milk, were fortified with it. An eight-ounce glass of milk contains about 100 International Units (IUs) of vitamin D.
By comparison, if you are Caucasian and expose 40 percent of your skin to midday summer sun in most of the United States, you will receive a dose of roughly 1,000 IUs per minute. The darker your skin, the less vitamin D you’ll receive from the sun. Anyone living north of about 35 degrees latitude–such as New York, Denver, Madrid (some high elevations excepted)–will receive none of the required wavelengths in midwinter.
UV light debate
Garland thinks he knows. He and his brother Frank kicked off the debate in 1980 when they published data showing that people living in higher latitudes had a greater chance of dying of colon cancer. They suggested that vitamin D had a protective effect.
Intrigued researchers conducted more studies. The “sunshine vitamin” became linked to so many other conditions, recalled Boston University physician and vitamin D researcher Michael Holick, that “when I first heard [the claims] I thought it was kind of crazy. How can it be doing so many things?”
But Holick became convinced of vitamin D’s effectiveness. “Heart, colon, prostate, brain, all those cells have receptors for vitamin D. We know it stimulates serotonin production [important in depression]. It is important for muscle function. It has a major role in keeping cell growth in check; it kills cells if they turn malignant.”
Holick and other proponents argue that humans evolved to get vitamin D from the sun and that scare tactics have convinced us to avoid it. Critics respond that hunter-gatherers didn’t live as long as modern humans, so nature may well have traded abundant vitamin D and great bones early in life for skin cancer after years of DNA damage.
And at least one major study has contradicted the overheated claims of vitamin D advocates. In 2006, new results from the Women’s Health Initiative, a huge federal study launched in the 1990s that focused on the benefits and risks of hormones for postmenopausal women, showed little benefit in participants who were given extra calcium and vitamin D. The supplements had no effect on colon cancer rates, cardiovascular disease, invasive breast cancer, and, most surprisingly, no effect on overall bone fractures (though it did strengthen hip bones), researchers found.