Link between diet and breast cancer

Diet alone is unlikely to be the "cause" or "cure" of cancer, says Prof Justus Apffelstaedt, Head of the Tygerberg Hospital Breast Clinic.

Diet is thought to be partly responsible for about 30% to 40% of all cancers. But diet alone is unlikely to be the "cause" or "cure" of cancer.

Findings in the past have suggested that physical activity, a healthy diet (particularly one low in fat and high in vegetables and fibre), and a healthy weight can help reduce the risk of breast cancer or the cancer coming back.

As we know, some risk factors for breast cancer cannot be modified, such as age and gender; however other factors such as diet, physical activity and smoking can be.

The large body of literature on nutrition and breast cancer has recently been reviewed and summarised by an international panel of the World Cancer Research Fund and the American Institute for Cancer Research. It was concluded that there is convincing evidence that:

• Alcohol intake raises the risk of breast cancer at all ages.
• Body fatness increases the risk of breast cancer after menopause and is probably related to a decreased risk of premenopausal cancer.
• Taller height is related to elevated risk of breast cancer, possibly because it is a marker for genetic, environmental, hormonal and nutritional factors affecting growth.

Due to the fact that diets vary widely between individuals and are usually difficult to establish in detail, the role of individual foods and nutrients on overall breast cancer risk drew limited evidence and no firm conclusions.

However, it was possible to summarise the findings of some food and vitamin specific findings:

• Red meat consumption could affect the risk of breast cancer because of the highly bioavailable iron content, growth-promoting hormones used in animal production, carcinogenetic heterocyclic amines (chemicals formed when muscle meat, including beef, pork, fish, or poultry, is cooked using high-temperature methods, such as pan frying or grilling directly over an open flame) and its specific fatty acids contents.
   
• Pooled analyses of case-control and cohort studies (Definition of cohort: a group of subjects who have shared a particular event together during a particular time span(e.g. people born in Europe between 1918 and 1939; survivors of an aircrash; truck drivers who smoked between age 30 and 40) have yielded conflicting results. However, recent reports suggest a positive association between the consumption of red meat and processed meat and the risk of breast cancer.
   
• When considering antioxidant intake, there is no consistent association between any antioxidant and breast cancer incidence. However, three studies have suggested a protective effect of vitamin E. In a Danish study, vitamin E intake has been related to a lower risk of breast cancer among postmenopausal women and two reports suggest a protective effect of high serum vitamin E on breast cancer risk.
   
• There is a suggestion that vitamin B12, a co-enzyme in folate (the form of folic acid naturally occurring in the body) metabolism, may be associated to lower risk of breast cancer and that low vitamin B12 intake may reduce the apparent protection in the risk for breast cancer conferred by folate.
   
• Fibre could play a role on the risk of breast cancer by decreasing the intestinal re-absorption of oestrogen and therefore lowering its circulating levels.

The level of carcinogenic exposure children and young adults have may be important in predicting later risk of breast cancer. This is because the mammary gland is most susceptible to environmental exposure before the accelerated cell differentiation during puberty and first pregnancy.

Nutrition in early life can affect height and age at menarche (the first menstrual cycle), which are established risks factors for breast cancer. Data from case-control studies suggests decreased risk for cancer with diets high in fat from dairy foods, milk, vitamin D and increased risk with high consumption of meat with visible fat.

Understanding dietary patterns and the impact they have on different populations is vital for hospitals, doctors and dieticians to make recommendations on eating practices to prevent disease.

Fruit, vegetables and glycaemic index

In studies mentioned in Diet and breast cancer by Isabelle Romieu, MD, MPH, ScD, it is suggested that vegetables have a protective effect against breast cancer. Vitamin E is also suggested to have a positive effect and a high intake of soy and phyto-oestrogen in adolescence in Asian populations is related to lower risk of breast cancer. Data from Mexico also suggests that high intake of folate and phyto-oestrogens are related to lower risk.

When it comes to women who have been through menopause, data from Singapore suggests that a diet rich in vegetable, fruit and tofu items has a protective effect on breast cancer and data from a large study conducted in French women supports the protective effect of a healthy/ Mediterranean pattern (essentially vegetables, fruits, seafood, olive oil and sunflower oil). Among the prospective epidemiological studies conducted on diet and breast cancer to date there is no clear association with diet except for alcohol consumption in addition to overweight and weight gain. Most of the studies have been conducted in Western countries with some limitations in variability of diet exposure. Few studies are available from middle to low income countries where variability in food intake is wider and food supplementation less prevalent.

On the other side of the coin, eating foods with a high glycaemic index during adolescence is associated with an increased risk of breast cancer. Data from Mexico also suggests that high intake of carbohydrate and high glycaemic load is related to an increase of breast cancer.

Although these results need to be confirmed in other populations, they suggest that baseline nutritional status and genetic susceptibility might interact with food intake in relation with breast cancer.

Written by Professor Justus Apffelstaedt, Associate Professor: University of Stellenbosch and Head: Breast Clinic, Tygerberg Hospital.

- (Health24, June 2012)

(Picture: Woman eating salad from Shutterstock)