Many people aren't waiting. Sales of the supplement in the United States were an estimated $425 million in 2009, up 82 percent from the previous year and 10 times what was spent in 2001, according to the Nutrition Business Journal.
An authoritative federal review due next month is expected to raise recommended amounts. But scientists on the panel, whose guidelines will affect medical practices, fortified foods, and everyday consumer purchases, are likely to be cautious. Most major research findings on Vitamin D are recent, and the amount required to overdose has not been definitively shown.
Some prominent scientists argue that such thinking is backward. Vitamin D, which is naturally produced in the skin in reaction to sunlight, is far more benign than a pharmaceutical. And with Americans spending more time on computers indoors and less time without sunscreen outside, surveys show that at least half - and up to 90 percent - do not have enough.
"We have this vast experiment going on," said Carol L. Wagner, a neonatologist at the Medical University of South Carolina in Charleston. "We are looking at the rampant Vitamin D deficiency throughout the country."
Continuing the status quo, she said, will harm far more people than would higher doses of a vitamin that her research has shown to be safe.
Wagner cowrote American Academy of Pediatrics guidelines that two years ago doubled the recommended Vitamin D intake for children to 400 IU (international units) a day and said obstetricians should consider screening all pregnant women for deficiency.
Last spring, she and colleagues reported the findings of their latest study completed by 350 pregnant women who were randomly placed into three groups. One group received 400 IU of Vitamin D daily, the amount that is in most prenatal vitamins and multivitamins. The other groups got either 2,000 IU or 4,000 IU, which happens to be the amount that Goldberg gave her pregnant patient with gestational diabetes.
The risk of a group of problems such as preterm labor, preterm birth, and all kinds of infections was reduced by 50 percent for those who got the highest amount compared with the lowest. Not a single adverse event was attributed to Vitamin D, and babies born to women in the highest group had significantly better levels of the vitamin in their blood.
Yet the research, presented at a big pediatrics meeting in Vancouver, was not formally discussed at a major OB/GYN conference in San Francisco two weeks later, and most obstetricians probably are unaware of it.
Vitamin D has been through this before.
As the Industrial Revolution moved families from farms to factories, pioneering doctors noticed that the serious bone deformities of childhood rickets were epidemic in polluted European cities but not in rural areas.
They treated the disease with sunlight but were ignored by the medical community until X-rays proved the case in the 1920s. The U.S. government recommended limited sun for children, and dairies began fortifying products with Vitamin D.
Rickets disappeared. The workings of Vitamin D - activated in the kidneys and critical for metabolizing calcium to build and maintain bones - had been unraveled.
Or so it was thought.
Over the last few decades, scientists have discovered that Vitamin D - technically not a nutrient at all but a hormone - regulates about 2,000 genes in different ways.
It plays a role in cell growth and death, and so has been linked to numerous cancers. It affects blood vessels, connecting it to high blood pressure and heart attacks. Its involvement with inflammation and the immune system brings an association with allergies and asthma, infections such as influenza and tuberculosis, and autoimmune disorders such as multiple sclerosis and type 1 diabetes.
In his recent book, The Vitamin D Solution, physician and researcher Michael F. Holick cites studies finding that the incidence of many of these conditions - hypertension, MS, nine kinds of cancer - is greater the farther you live from the equator.
Dark-skinned people, who migrated to Northern latitudes relatively recently in human history, require more exposure to direct sunlight to produce the same amount of Vitamin D as those with lighter skin. African Americans' average Vitamin D levels are the lowest of any racial group - possibly helping to explain, Holick says, why studies show blacks suffer disproportionately high rates of several diseases even if they have equal access to health care.
He also believes that rising rates of some diseases are tied to Americans' love affair with sunscreen.
Vitamin D advocates urge limited sun exposure. The dermatologists' message is to not go out unprotected.
It's not that dermatologists are against Vitamin D.
The link between too much sun and skin cancer is known but complex, said Christopher J. Miller, director of dermatologic surgery at the Hospital of the University of Pennsylvania. On the other hand, the link between too little sun and other cancers is intriguing but not proven.
Plus, "you can get Vitamin D in other ways," Miller said: from supplements and diet.
Getting it from diet means fortified foods, the main source for the vast majority of Americans. The amount of Vitamin D they contain has not changed since the 1930s. To ingest what advocates now consider to be enough - 1,000 to 4,000 IU - would mean drinking 10 to 40 cups of milk a day or eating between a half-pound and two pounds of salmon or mackerel, fatty fish that are among the few significant natural food sources.
Vitamin D supplements can easily provide enough, and holistic doctors have been recommending several times the current guidelines for years. But others worry about toxicity.
"We are very reluctant to give pregnant mothers any medications," including "super vitamins," said Owen Montgomery, chairman of obstetrics and gynecology at Drexel University College of Medicine.
He said the latest research, while striking, is not enough to "change anyone's practice. I think what it should do is generate more funding for larger studies."
Pretty much everyone agrees that there should be more research. They also agree that Vitamin D deficiency is getting worse, even though no one knows what's normal because sophisticated tests used to measure levels in the blood didn't exist before civilization blocked out the sun. And doctors of all stripes concur that current federal guidelines are hopelessly out of date.
"We've been off by a factor of 10," said Holick, the author and a professor at Boston University School of Medicine. Holick was a member of the panel that set current federal guidelines in 1997 and he gave expert testimony to the committee that is updating them now.
He and others predict that the recommendations due out next month will call for modest increases that might make a small difference in the nation's health.
The caution would be the lack of good evidence.
Despite thousands of studies, there is not a lot of strong research - large, controlled, randomized trials that are the gold standard for medical studies - showing consistent benefits from Vitamin D, said Joseph Lau, director of the Tufts Evidence-Based Practice Center in Boston, which compiled a 400-page review of the data for the Institute of Medicine panel.
Vitamin D researchers say that's partly because of a catch-22: The 1997 panel set an upper tolerable limit that scientists cannot exceed without special permission from the Food and Drug Administration. The limit had to be based on research available at the time - almost none - and experts say it is so low that most studies even now don't give enough to find a real benefit.
And it can be harder to prove a significant benefit in a study of a common nutrient compared with a new drug. "If you give some Vitamin D to one group but not the other one, but the other group may be exposed to sun more or eat different kinds of food, it becomes really difficult to compare," Lau said.
Nevertheless, more than 1,000 Vitamin D studies have appeared just since Lau's evidence review was submitted to the federal panel in August 2009. Some of the most striking findings were published by a team at the Intermountain Medical Center in Utah: Among its 27,686 patients at least 50 years old who had a Vitamin D test in the last decade, heart failure was 90 percent more common in those with the lowest vs. the highest levels; a previous heart attack was 81 percent more likely; a previous stroke was 51 percent more likely.
The association does not prove cause and effect. It is quite possible that a heart condition lowers Vitamin D levels either directly or indirectly, by keeping invalids indoors and out of the sun.
But the link was so strong, the researchers wrote in the Oct. 1 issue of the American Journal of Cardiology, that their "findings, taken in the context of previous observations, suggest that Vitamin D deficiency represents an important new CV risk factor."
"We're really where we were in the 1970s and 1980s with cholesterol," lead author Jeffrey L. Anderson said. Large clinical trials first proved that cholesterol-lowering drugs could reduce risk of death in the mid-1990s.
While the University of Utah School of Medicine cardiologist believes that more study is needed, he draws on his own knowledge of Vitamin D when seeing patients.
"I personally advise them to take it at the moment because I think that it is safe and it is good for other reasons for sure," he said. "I can't see that there is harm."
The Vitamin D Debate: How Much Do You Need?
Current supplement guidelines are not enough . . .
Every 100 IU of Vitamin D (the amount in one cup
of fortified milk) consumed daily raises the level of Vitamin D in the blood by about 1 ng/mL.
Federal guidelines vs. Experts' advice
AI* RDA* Holick** Hollis***
Birth to age 50 200 400 **
Pregnant women 200 400 1,400-2,000 4,000
Lactating women 200 400 2,000-6,000 6,000
Age 51 to 70 400 400 1,500-2,000**
Age 71 and older 600 600 1,500-2,000
Upper limit 2,000 10,000
* AI: "Adequate Intake" (minimum considered necessary). RDA: "Recommended Dietary Allowance" (simplified to apply to most people and translated on product labels as % of Daily Value). Both are based on Institute of Medicine reports.
** Michael F. Holick, Boston University School of Medicine, recommends 400-1,000 IU per day from birth to 1 year, 1,000-2,000 to age 12, and 1,500-2,000 for age 13 and over. He also recommends two to three times these amounts for obese people.
*** Carol L. Wagner and Bruce W. Hollis, Medical University of South Carolina.
. . . to raise Vitamin D to adequate levels
Surveys show that at least half and up to 90 percent
of Americans have below-normal levels* of Vitamin D. There is no universal definition of "normal," although these are common.
In nanograms per milliliter (ng/mL):
Mainstream medicine vs. Experts/holistic doctors
Very low Low Normal Normal
Under 20 20-30 Over 30 40-80
* The level is determined by a blood test that a physician can order, and typically is covered by insurance. It costs between $50 and $250 without coverage.
SOURCES: Inquirer research
Contact staff writer Don Sapatkin at 215-854-2617 or firstname.lastname@example.org.