As recently as a decade ago, vitamin D was mostly thought of as a helper-nutrient - it allowed the body to absorb and use calcium for strong bones. With a diet of fortified foods and a little bit of sunshine every day, most people got plenty of it.

But that was years ago. Today, research suggests that vitamin D does much more than help build strong bones, and the findings come at a time when a high number of people are no longer getting enough of the nutrient, doctors say.

"We've become a culture that shuns the sunshine and doesn't drink milk," said Dr. Donald Abrams, chief of hematology-oncology at San Francisco General Hospital.

As a result, doctors are seeing a small resurgence of rickets and are concerned about osteoporosis in adults over age 50, especially as Baby Boomers get older.

Known for causing bowed legs, fractured bones and poor growth primarily in children, rickets all but disappeared in the United States decades ago as diets improved and vitamin D was added to certain dairy products like milk.

Vitamin D's moment

To remedy the low vitamin D levels they are seeing, doctors are beginning to recommend supplements to their patients, and more of the vitamin than recommended by national guidelines. That is largely because research over the past decade has increasingly suggested that vitamin D plays a far bigger role in overall health than previously believed.

Aside from its well-known reputation for building and maintaining strong bones, vitamin D could be tied to cancer prevention and cardiovascular health, and some researchers are looking into a connection between vitamin D deficiency and gum disease, said Dr. Mark Ryder, chair of the division of periodontology at the UCSF School of Dentistry.

"It helps boost your ability to fight infection, and it also reduces some destructive inflammation in your body, including inflammation with periodontal disease," Ryder said. "Every five or 10 years, a new vitamin becomes the vitamin of the moment. The hot one right now is probably vitamin D, and so far all of the evidence looks encouraging."

If, in fact, vitamin D is more important than believed, people probably need more of it than they're getting - and more than doctors have recommended in the past, Ryder said.

More D is better

National guidelines recommend between 200 and 600 international units of vitamin D a day. Doctors say it's unclear exactly how much vitamin D people should be getting, but 1,000 international units a day is a good place to start. It is possible, but unlikely, to get too much vitamin D - some studies say people can safely take 10,000 units a day and suffer no ill effects.

"I recommend to my patients who are older that they take between 800 and 1,200 units a day, unless they have certain diseases that cause poor absorption, and then they may need more," said Dr. Jerry Minkoff, an endocrinologist with Kaiser Permanente in Santa Rosa. "I don't own stock in Nature's Blend, but yes, people should just take a supplement. It's very cheap, and it's very safe."

National studies suggest that about two-thirds of Americans currently meet vitamin D recommendations, but many doctors say those guidelines are outdated. Abrams, the hematology-oncology expert at San Francisco General, said vitamin D deficiency has become so common in his patients that he routinely recommends a supplement, even without a test to confirm whether they're getting enough of the nutrient.

There often are no symptoms from low vitamin D levels except in cases where the deficiency is so great that rickets or osteoporosis result. Some people may feel tired or sluggish and find they have more energy when they take a vitamin D supplement, but there are no clinical trials to prove those effects.

The supplement typically comes in pill form, but people can get vitamin D naturally from sun exposure and by eating certain foods. Both of those options are problematic, however.

It might only take a few minutes of sun exposure every day to create enough vitamin D, but doctors are wary to recommend spending time in the sun because of the risk of skin cancer. Wearing sunblock prevents vitamin D production.

Cod liver oil is the best source of vitamin D - it has 1,360 units in a tablespoon. But it tastes awful.

Most other foods with vitamin D just don't have enough of it to be practical sources. Salmon and some other fish have a few hundred units of vitamin D per serving, but most people don't eat enough fish to reliably get the nutrients they need every day. Two cups of fortified milk a day would meet the current vitamin D recommendations - but few Americans drink that much.

"There are ways of getting vitamin D naturally. But how much you can eat of these things is another issue," Minkoff said. "I think you'd have to drink a quart of milk a day to get enough. That's a lot of lattes."