IT IS the staple sandwich filling in school lunchboxes across the land. But cancer experts today warn parents not to give their children ham which, along with other processed meats such as salami, hot dogs and bacon, increase the risk of bowel cancer.
A report by the World Cancer Research Fund (WCRF) says there is "convincing evidence" of the link between processed meats and bowel cancer in later life. While there is no specific research on eating the meats in childhood, the charity said the evidence in adults was too strong to ignore.
Children should therefore adopt a healthy eating pattern from the age of five and avoid processed meat, the report said.
WCRF's children's education manager Marni Craze said: "If children have processed meat in their lunch every day then over the course of a school year they will be eating quite a lot of it.
"It is better if children learn to view processed meat as an occasional treat if it is eaten at all."
Scientists estimate about 3,700 bowel cancer cases could be prevented each year in the UK if everyone ate less than 70g of processed meat a week – roughly the equivalent of three rashers of bacon.
A recent survey showed that two-thirds of people in Britain were unaware that eating processed meat increases the risk of cancer.
In 2007, the WCRF issued a report – Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective – based on a detailed review of more than 7,000 clinical studies covering the links between cancer and diet.
Its experts recommended avoiding processed meat altogether and eating less than 18 ounces of red meat a week.
Processed meats are usually manufactured using sodium nitrite, a colour fixer which is carcinogenic.
David Bartolo, a consultant colorectal surgeon at the Western General Hospital in Edinburgh, said: "There is a lot of evidence that diet and bowel cancer are related. While processed meats contain salt which affects blood pressure and is a factor in strokes, they also contain nitrates which we've known are promoters of cancer in the stomach and gullet. But I struggle to say it's processed meat rather than ordinary meat which is causing the problem.
"Probably the most important factor in bowel cancer is obesity. As body weight rises so do cases of bowel cancer. Food is to some extent toxic to us so it is a matter of getting the right balance.
"People should increase the amount of fresh fruit and vegetables they eat, take exercise and not eat red meat every day. In an ideal world, if we were living like our ancestors, it would be a treat eaten perhaps once a week."
The WCRF is also urging parents to avoid lunchbox fillers that are high in fat and calories.
Foods such as sugary drinks can cause weight gain, and obesity in adulthood is linked to cancer, it said.