Madam, - I am writing to express concern about the article "Milk and breast cancer debate" (Health Supplement, November 14th). Citing the theories of Jane Plant, the article contains several glaring inaccuracies about diet and breast cancer and fails to provide a balanced scientific argument surrounding such an emotionally charged issue affecting many Irish women.
Perhaps the most alarming is Plant's statement, "if you keep taking dairy products, you are promoting cancer cells". It is outrageous that a sweeping statement of this nature can appear in an esteemed publication such as The Irish Times without evidence to support it.
The influence of diet on breast cancer has been extensively studied and it has proved impossible to link breast cancer risk with any one single dietary component. The risk of breast cancer is multifactorial, involving family history, environment and lifestyle factors such as diet. Plant's decision that the low rate of breast cancer in China is related to Chinese women's low intake of dairy foods does not stand up to scientific scrutiny. Despite quoting epidemiological evidence, she fails to acknowledge a comprehensive review from 2004 of 46 epidemiological studies from 20 countries which concluded that breast cancer risk was not related to consumption of dairy products.
In 2005, an examination of 53 studies found the overwhelming evidence indicated no relation between dairy foods and breast cancer risk and, indeed, may even suggest a protective role. It is too simplistic to equate the incidence of breast cancer in Asian women to a lack of dairy products in the diet because, compared with women in Western countries, Asian women are less overweight, consume less alcohol and have their babies earlier. All of these factors have been implicated in breast cancer risk.
The crux of Plant's theory is based on the notion that dairy products are a source of IGF-1 (Insulin-like growth factor 1), which may cause breast cancer. No evidence was offered to support this theory. Indeed, there is no published data to suggest that IGF-1 is absorbed from milk or other dietary sources and enters the blood stream. As a protein, IGF-1 is broken down by the digestive enzymes in the gut into amino acids or peptides, thus destroying its growth-promoting activity. In fact, the majority of circulating IGF-1 is produced within the body and is not derived from food sources. Cancer cells themselves produce IGF-1, so it will be observed in the blood of a cancer patient. Dairy foods actually contain a number of components postulated to reduce breast cancer risk, including calcium, vitamin D and conjugated linoleic acid (CLA). A major study of over 48,000 women in Norway found that women consuming three or more glasses of milk a day had a 44 per cent lower incidence rate of pre-menopausal breast cancer than those women not drinking milk.
The article also refers to Plant's theory regarding high-acid diets and osteoporosis risk, stating incorrectly that "the root cause of osteoporosis is not lack of calcium but an excess of protein". Like breast cancer, osteoporosis is a disease characterised by many risk factors, of which diet is only one.
According to the National Institute of Health in America, calcium is the specific nutrient most important for attaining peak bone mass and for preventing and treating osteoporosis. Furthermore, in persons with an adequate intake of calcium, high dietary intakes of protein do not adversely affect calcium balance or bone health. Dairy products are the main contributor to calcium in the Irish diet.
Currently in Ireland, 36 per cent of Irish women have inadequate calcium intakes, and one in three will experience an osteoporotic fracture at 50 years. Unfortunately, this article runs the risk of compounding this problem. A balanced diet, including three portions of dairy products per day and adequate fruit and vegetables, combined with weight bearing physical activity, are important for achieving good bone health.
Many women are concerned about breast cancer, and rightly so. But it is vitally important that any advice given to them is well founded and backed by scientific evidence. - Yours, etc,
HILDA GRIFFIN,
Nutritionist,
National Dairy Council,
Dublin 2.
The interview with Prof Plant was accompanied by sceptical comments from Action Breast Cancer and the Irish Osteoporosis Society. - Ed., IT.