Jun. 19--A team of Norwegian researchers has produced provocative clues about bone density, vitamin D and breast cancer.

At the recent annual convention of the American Society of Clinical Oncology, the largest meeting in the world of cancer specialists, Dr. Per Lonning of Haukland University Hospital in Bergen, Norway, said that low vitamin D levels could be a risk factor for the malignancy.

He suggested that maintaining adequate levels of the nutrient, known commonly as the sunshine vitamin, may be a way to prevent the cancer.

The suggestion is by no means definitive.

Lonning's hypothesis evolved through observations in a larger study on bone density in women taking the breast cancer drug Aromasin, a type of anti-cancer medication known as an aromatase inhibitor. Lonning found that women who had the lowest blood levels of the vitamin were most likely to experience fractures.

Additional examination of the data revealed that women with low levels of the nutrient were more likely than those with higher levels to experience a cancer rebound.

Investigators in this country who studied vitamin D along with calcium intake say their research was inconclusive.

"Our findings suggest that calcium and vitamin D supplementation may reduce breast cancer risk in some women, but more research is needed to clarify these results," Dr. Rowan Chlebowski, lead investigator of the Women's Health Initiative told the same cancer conference, which met two weeks ago in Atlanta.

"We can't yet make a general recommendation about how much calcium and vitamin D individuals should take," Chlebowski said. The researchers studied breast cancer incidence in 18,176 women randomly selected to take 1,000 milligrams of calcium carbonate and 400 international units of vitamin D daily and compared the findings to 18,000 women who took a placebo.

Chlebowski and his team concluded that neither nutrient could be recommended as a breast cancer preventive because breast cancer incidence did not differ dramatically between those who took supplements and those on a placebo.

Dr. Lora Weiselberg, chief of breast cancer services at North Shore University Hospital in Manhasset, said vitamins are not magic bullets. "I would caution the lay public against high doses of vitamin D because it can accumulate in the body, especially the liver," she said.

As provocative as emerging theories seem, "There is no evidence that vitamin D will lower the risk of breast cancer. The hard science to address this has yet to be done," she said.

Scientists at the Samuel Lunenfeld Research Institute in Toronto reported in April that vitamin D may be involved in lowering breast cancer risk. The Canadians discovered the reduction to be most prominent among women who were exposed to the highest levels of vitamin D when they were young.

A team at the University of California, San Diego also suggested earlier this year that obtaining extra vitamin D through dietary sources may help stave off the cancer.

Vitamin D is a fat-soluble vitamin essential for maintenance of normal calcium levels. It comes in two forms. Vitamin D3 is synthesized in the skin upon exposure to ultraviolet-B radiation from sunlight. Many types of plants synthesize vitamin D2.

When exposure to ultraviolet light is insufficient for the synthesis of healthy amounts of vitamin D3 in the skin, consuming vitamin D through dietary sources, such as fortified milk, fish, some ready-to-eat cereals and eggs, becomes essential.

"It would be wonderful if we could have interventions like this, but vitamin D has to be respected because of its potential for toxicity," Weiselberg said.

-----

Copyright (c) 2006, Newsday, Melville, N.Y.

Distributed by Knight Ridder/Tribune Business News.