Evidence continues to pile up that the sunshine vitamin protects against much more than bone-softening rickets. Vitamin D, also found in milk and oily fish, is becoming king, from fighting colds to preventing cancer.

But here's the kicker. New research suggests we're not getting nearly enough, and recommended levels may be woefully inadequate.

Investigators at the Medical University of South Carolina shut down part of a National Institutes of Health study that left nursing mothers and infants deficient, even though the mothers received the maximum safe amount of vitamin D allowed by the Institute of Medicine.

Bruce Hollis, primary investigator and MUSC professor of pediatrics, said the recommended 200 international units a day for babies, children and adults is grossly deficient. Further, the 2,000-unit-a-day upper limit — the highest safe dose — established a decade ago by the Institute of

Medicine is "totally false."

In the trial, half of mothers given 2,000 units a day did not receive enough vitamin D to pass to their babies. For years, the medical community has pondered the perfection of human milk for babies except its one shortcoming: deficient levels of vitamin D. The answer may be simple, Hollis said. "It's deficient in vitamin D because mothers are."

The five-year trial studying nursing mothers began two years ago with a $5-million NIH grant to determine how much vitamin D nursing mothers needed to supply their infants with enough.

Dr. Robert Heaney, a vitamin D and calcium expert at Creighton University in Omaha, Neb., was on the panel that set the vitamin D levels in the mid-1990s. "Most of what we've learned about vitamin D has been in the last decade," Heaney said in a phone interview. "It does jillions of other things than prevent rickets."

Vitamin D is necessary for the blood to maintain healthy levels of calcium and phosphorus. The supplement lowers risk for breast, prostate and colon cancers, Heaney said. It also reduces risk for Type 1 diabetes, hypertension and multiple sclerosis, and improves resistance to infections.

The average person needs about 4,000 units of vitamin D to maintain a healthy level in their bodies, Heaney said. The usual sources of Vitamin D include brief exposures to the sun, such as walking to your car, multivitamins, milk and oily fish.

Even with all those sources, many people don't get enough, he said. Unless you work or spend a lot of time outdoors, Heaney recommended 1,000 to 2,000 units in addition to other sources of vitamin D.

But whether or not to seek that extra vitamin D in the sun is a point much debated among experts. No one would argue for browning oneself on the beach for hours, but some researchers suggest between five and 30 minutes twice a week without sunscreen.

In light of the growing body of research, the American Academy of Pediatrics doubled its recommended dose to 400 units for newborns. "Regulations do not change rapidly," Heaney said. "That's why the work in South Carolina is so important."

The MUSC study formed three groups of nursing mothers with participants in the Lowcountry and a secondary site in Rochester, N.Y. In one group, mothers and babies received 400 units each, as per the academy's recommendation. Mothers in that group ended up grossly deficient, Hollis said, but most of the babies, who are smaller, received enough of the supplement.

A second group of mothers was given 6,000 units a day, three times the maximum dosage, and the babies did not receive supplements. Mothers and infants in this group were largely OK, Hollis said.

In the third group, mothers were given 2,000 units, and babies were not given extra vitamin D. Half of the babies in this group failed to receive enough vitamin D, leading Hollis and co-primary investigator, Dr. Carol Wagner, to close that study group.

By comparison, only 5 percent of babies from the two other groups did not receive enough vitamin D, a rate likely due to participants not following directions, he said. The decision to halt the trial group was based on the babies', not the mothers' levels, he said. Moms in the 2,000-unit-a-day group were borderline deficient.

"When you stop an arm of an NIH study, that's a big deal," he said. The remaining groups will continue three more years.