The studies have produced evidence that low levels of Vitamin D make men more likely to have heart attacks, breast and colon cancer victims less likely to survive, kidney disease victims more likely to die, and children more likely to develop diabetes. Two other studies suggested that higher Vitamin D levels reduce the risk of dying prematurely from any cause.

In response to these and earlier findings, several medical societies are considering new recommendations for a minimum daily Vitamin D intake, the American Medical Association recently called for the government to update its guidelines, and federal officials are planning to launch that effort.

But many leading experts caution that it remains premature for people to start taking large doses of Vitamin D. While the new research is provocative, experts argue that the benefits remain far from proven. Vitamin D can be toxic at high doses, and some studies suggest it could increase the risk for some health problems, experts say. No one knows what consequences might emerge from exposing millions of people to megadoses of the vitamin for long periods.

“The data are intriguing and serve as, no pun intended, food for further fruitful research,” said Mary Frances Picciano, at the Office of Dietary Supplements of the National Institutes of Health. “But beyond that, the data are just not solid enough to make any new recommendations. We have to be cautious.”

The current clash is the latest in a long, often unusually bitter debate. Some skeptics question whether funding by the tanning, milk and vitamin industries is biasing some advocates. Frustrated proponents accuse skeptics of clinging to outdated medical dogma.

“It feels kind of ridiculous working in this field sometimes,” said Reinhold Vieth, a professor of nutritional sciences and pathobiology at the University of Toronto. “Every week, I get interviewed about the next important publication about Vitamin D. But this field remains mired in the muck.”

Vieth is one of a small but vocal cadre of researchers pushing doctors and patients to stop waiting for new official guidelines. Physicians should routinely test their patients for Vitamin D deficiencies, and more people — especially African Americans — should take supplements and increase their exposure to the sun, they say.

“The bottom line is we now recognize that Vitamin D is important for health for both children and adults and may help prevent many serious chronic diseases,” said Michael F. Holick, a professor of medicine, physiology and biophysics at Boston University.

Scientists have long known that Vitamin D is a vital nutrient the skin produces when hit by ultraviolet light from sunlight and other sources. The amount of Vitamin D produced varies, depending on where the person lives, skin pigment, age and other factors. African Americans and other dark-skinned people, and anyone living in northern latitudes, make far less than other groups.

With people spending more time indoors surfing the Web, watching television, working at desk jobs, and covering up and using sunblock when they do venture outdoors, the amount of Vitamin D that people create in their bodies has been falling. Milk and a few other foods are fortified with Vitamin D, and it occurs naturally in others, such as fatty fish, but most people get very little through their diets.

“Humans evolved in equatorial Africa wearing no clothes,” said Robert P. Heaney, a leading Vitamin D researcher at Creighton University in Omaha. “Now we get much less direct sunlight, and so we don’t make nearly as much Vitamin D.”