High dietary phosphate intake may promote skin cancer formation

A high dietary intake of phosphate promotes tumour formation in an animal model of skin cancer, researchers at Emory University School of Medicine have found.

The results, published in the journal Cancer Prevention Research, suggest that a high intake of phosphates may promote tumour development and contribute to tumour growth in skin cancer, while restricting phosphate intake may help prevent cancer.

The researchers applied dimethylbenzanthracene, a carcinogen found in cigarette smoke, to the skins of mice, followed by another chemical that stimulates cell growth.

Feeding these mice a high phosphate diet (1.2 percent by weight) increased skin papilloma number by 50 percent compared with a low phosphate diet (0.2 percent).

Skin papillomas are the initial stage of skin cancer development, which may progress to full carcinoma.

"This is a very well established model for the initiation and progression of cancer, and the effects of many physiological conditions on cancer initiation have been measured this way," says senior author George Beck, PhD, assistant professor of medicine (endocrinology). Beck is also a member of the Winship Cancer Institute, Emory University.

Phosphate is an essential nutrient forming both the physical support for bones, when complexed with calcium, and the chemical backbone of DNA. Phosphate chemical bonds provide the energy currency in the cell, in the form of ATP (adenosine triphosphate).

In addition, many oncogenes, the motors driving cancer cells to divide relentlessly, are regulatory enzymes that attach phosphate chemically to other proteins, turning their activity up or down depending on the protein target.

Altered levels of phosphate could be tipping the balance of these chemical reactions in complex ways, Beck says.

Public health researchers say that phosphate dietary intake has increased over the last 30 years and also may be underestimated because of the increasing contribution of food additives.

Phosphate is added to a variety of processed foods such as meats, baked goods and soft drinks to improve texture and durability.

The authors calculate that the human dietary equivalent of a mouse's high phosphate diet is 1,800 milligrams per day, an intake level that many humans match or exceed.

The high-phosphate diet did not have a corresponding increase in calcium, which would reflect the equivalent of a dairy-rich diet. A low-phosphate diet in the mice corresponds to 500 milligrams per day for humans.

"Another way to look at it is that a low-phosphate diet may help prevent cancer," Beck adds.