NEW YORK (Reuters Health) - The findings of a series of animal studies indicate that calcium deficiency, which accelerates the rate that calcium is absorbed back into the bone, promotes breast cancer tumor growth in bone, Australian researchers report.

"Calcium deficiency, due either to low calcium in the diet or to vitamin D deficiency, is very common in older women, who are also the population at highest risk of breast cancer and breast cancer bone metastases," lead researcher Dr. Colin R. Dunstan pointed out to Reuters Health. Metastasis occurs as cancer progresses and the cells spread from the primary site to attack other areas of the body.

Dunstan of the ANZAC Research Institute in Concord and colleagues conducted dietary studies in a mouse model of breast cancer growth in bone. The results are published in the journal Cancer Research.

The researchers found that after breast cancer tumor was implanted into the animals, the mice that were feed a diet containing only 0.1 percent calcium showed signs of high bone turnover compared with the animals feed a diet with a normal 0.6-percent calcium content.

By day 17, the mice on the low-calcium diet had a 43-percent increase in bone destruction, a 24-percent increase in tumor area, and a 24-percent increase in cancer cell proliferation compared with the mice on a normal diet.

The team also found that treatment with osteoprotegerin, to counteract the absorption of calcium into the bone, completely inhibited bone destruction, reduced tumor area, decreased cancer cell proliferation, and increased the death of cancer cells.

Dunstan pointed out that "calcium and vitamin D deficiency are easily assessed and corrected." Therefore, research in women with a high risk of breast cancer metastasis is "urgently required" to see of calcium deficiency or vitamin D deficiency are risk factors for disease progression.