As far as Dr. Joseph Mercola is concerned, Vitamin D is the magic bullet we've all been looking for. A lack of this wonder nutrient, the controversial natural health advocate says, can set the stage for no fewer than 33 disorders, including autism, cancer, diabetes and infertility.
"Vitamin D appears to reduce your risk of dying from virtually ANY disease," he wrote on his popular Web site. His recommendation? Get more sun, relax in a tanning bed or try supplements such as "Sunshine Mist," a vitamin D spray he sells.
Long ignored and feared in high doses, vitamin D is now being hailed as the answer to nearly every health issue under the sun. The excitement stems from a flurry of preliminary studies finding links between vitamin D deficiencies and various illnesses, and this summer the federal Institute of Medicine plans to announce revised recommendations regarding dietary intake of vitamin D and calcium that almost certainly will be higher.
But despite the scientific attention being paid to vitamin D, experts caution that claims of wide-ranging health benefits are not yet supported by clinical evidence.
Though D is thought to hold tremendous promise, we've been down this garden path before: Hopes for the powers of vitamin E, beta carotene, antioxidant vitamins, selenium and other nutrients collapsed under the weight of rigorous randomized clinical trials.
"It's premature to go out and make a big deal out of vitamin D supplementation when we don't have the evidence," said endocrinologist Anastassios Pittas, co-director of the Diabetes Center at Tufts University Medical Center. "We've been burned before on nutrition-based interventions," he said.
Yet already bread, pasta, orange juice and soy foods are being fortified with vitamin D, and sales of vitamin D supplements grew 116.5 percent from 2007 to 2008, from $108 million $234 million, according to estimates from Nutrition Business Journal.
The body naturally makes the vitamin when the sun's ultraviolet rays hit the skin, but fear of health risks and modern lifestyles have limited sun exposure for many.
Mercola, a non-practicing osteopathic physician who owns a clinic in Hoffman Estates, Ill., is one of the nutrient's most public and ardent supporters, with an evangelical style that can grate on the nerves of more cautious physicians.
Unlike most doctors, Mercola recommends universal baseline testing and widespread high-dose supplementation. "I've been preaching about this for a long time," said Mercola, who started his campaign 10 years ago. "Eventually the evidence comes out."
Mercola said children should get almost six times the amount of vitamin D currently recommended by the American Academy of Pediatrics, while adults and pregnant women should be receiving 5,000 IUs per day.
Most leading vitamin D researchers recommend no more than 1,000 to 2,000 IUs a day to the general public, citing insufficient evidence for higher doses. The current federal guidelines, which are widely considered to be woefully inadequate, range from 200 to 600 IUs, depending on age.
"Dr. Mercola popularizes and promotes vitamin D in a very passionate way," said Dr. Gregory Plotnikoff, a senior consultant at the Center for Healthcare Innovation in Minneapolis who is conducting vitamin D trials. Mercola's high dosing recommendations "may be correct, but we need supportive data," he said.
Still, Plotnikoff and other researchers have high hopes for the vitamin, saying it could prove to be the single most cost-effective medical intervention in the U.S. today.
Best known for preventing rickets in children - the reason it is added to milk - vitamin D shines most in the role of absorbing calcium, which we need to form bones. A deficiency of vitamin D can contribute to osteoporosis by reducing calcium absorption.
Unlike vitamin E and others, vitamin D is a potent steroid hormone that has receptors in most, if not all, cells of the body. Mounting evidence suggests the so-called "sunshine vitamin" may also influence conditions unrelated to the skeleton, including cardiovascular disease, hypertension, diabetes, cancer, autoimmune disorders and overall mortality, said Dr. Michael Hollick, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University Medical Center.
"Vitamin D is as important for every cell in the body as thyroid hormone, estrogen and testosterone," said Plotnikoff. "These hormones turn on and off genes in our DNA. At least 1,000 key genes are under at least partial control by vitamin D. This was never the case for vitamin C, E and others."
Though observational studies have found a link between low vitamin D levels and an increased risk of disease, such an association doesn't prove a deficiency caused the problem. Low levels of D could also be a consequence of the illness.
The results of studies can also be skewed by the people participating (vitamin D trial subjects are disproportionately white-skinned) or if the research does not account for sunlight exposure or consumption of D in foods. The doses studied are sometimes too low, experts also say.
When Pittas and his colleagues systematically reviewed studies on vitamin D's effect on type 2 diabetes, hypertension and cardiovascular disease, for example, they found "no clinically significant effects at the dosages given," according to the research published last week in the Annals of Internal Medicine. They called the vitamin a "promising but unproven" new factor in cardiometabolic disease management.
"There's a potentially large problem with leaping from observational studies to making decisions about interventions," said Dr. Ethan Balk, associate director of the Center for Clinical Evidence Synthesis at Tufts Medical Center, a co-author of the Annals study.
"Advocates take the studies and say: 'If we can move someone's vitamin D from low to high, the risk would go down.' While that might be the case, there may be another explanation," said Balk.
In some ways, it's much easier to study drugs than nutrients because "everyone starts a pharmaceutical study at the same point, namely ... zero," said Plotnikoff. "In contrast, everyone starts a nutritional study with baseline measurements all over the map. Everyone is given the same dose as if one size fits all. This is a huge mistake."
Drug effects, meanwhile, tend to be immediate, focused and measureable, while vitamins may have long-term, subtle effects.
Proponents also may oversell the study findings. Mercola's Web site, for example, recently headlined an item on a new study this way: "Vitamin D fights Crohn's disease." But the lead researcher, Dr. John White of the Research Institute of McGill University Health Center in Montreal, said the data came from a lab study that "will have to be born out in the clinic, which may be tricky."
"Data is coming, but there's a good reason to be skeptical; people have been on this bandwagon before," said White, an endocrinologist. "When it gets into the clinic, it often doesn't work out quite as well."
The debate over optimal amounts of vitamin D and how to get it, meanwhile, is ongoing and will likely not be settled by the new NIH guidelines.
But one thing is clear: Vitamin D levels are lower than they were 20 years ago. Most Americans - especially those with dark skin - are likely deficient, the result, some say, of widespread campaigns for sunscreen use and sun avoidance as well as smog and cloud cover, living indoors and rising national trends for inactivity and obesity.
Cardiologist Diane Wallis is one doctor who will continue to test her patient's vitamin D levels, even though it's an unproven treatment in her field. "We're at the threshold," said Wallis, of Midwest Heart Specialists in Downers Grove, Ill., who, 10 years ago, began seeing female patients with chest pain but no obvious signs of heart trouble. When she tested them, they all had one thing in common: Low vitamin D levels. "When I started it we'd just gotten off the whole Vitamin E fiasco and people thought I was crazy," she said. "Anything that had the word 'vitamin' led to derision. But no one is making fun of it anymore."Copyright © 2015, The Baltimore Sun