Wednesday September 2 2009
Many factors contribute to the risk of breast cancer
A 'slob lifestyle' increases the risk of breast cancer risk according to the Daily Mirror, while the Daily Mail has estimated that 18,000 women a year could be saved from the disease by exercise and dieting. It is reported by The Times that scientists have found “the strongest evidence yet” that lifestyle is linked to breast cancer risk and that over 40% of cases could be prevented by limiting alcohol intake, maintaining a healthy weight and exercising.
Where is the research from?
The World Cancer Research Fund (WCRF) has updated its 2007 review of the body of literature surrounding the associations between food, nutrition, physical activity and the risk of breast cancer. To update the findings of their Global Report published in 2007, the WCRF searched the Medline database and obtained 100 relevant study reports published between January 2006 and May 2008.
The studies included had variably assessed many dietary pattern types (e.g. vegetarian), food groups (e.g. vegetables and cereals), individual foods (e.g. grapefruit and soy), beverages, food preparation methods, dietary constituents (e.g. vitamins and fibre), physical activity, energy balance and body measurements.
From within each study the researchers identified risk estimates for breast cancer from the relevant exposures, giving preference to those that had been statistically adjusted to account for possible confounding factors such as age. Results were reported in relation to menopausal women, premenopausal women or women where menopausal age was unspecified.
What were the findings of the report?
The report is extensive and detailed, comparing and combining the results of a large number of studies. The review also includes the findings of all those individual studies that assessed possible risk factors between food, nutrition and physical activity and the risk of breast cancer.
The full report features a lot of information but the findings on some potential risk factors assessed are summarised below.
For each 10g increase in pure alcohol consumption per day there was an associated increase of 8% in the risk of breast cancer. This increase was significant and the risk was increased for both pre- and post-menopausal women. The WCRF panel consider there to be convincing evidence for an increase in risk with increased alcohol consumption.
Meat and fish consumption
There was a general trend across studies for an increased risk of breast cancer with higher red meat consumption, although in the majority of studies, these results were non-significant. There was also a trend for increased risk with higher processed meat consumption, although, again, most results were non-significant. A similar pattern was seen for the consumption of unspecified types of meat. There was no consistent evidence across numerous studies on fish intake, with most studies giving non-significant results.
Fruit and vegetable consumption
There were minimal studies on cruciferous (e.g. cabbage, radish and broccoli) vegetable intake, green leafy vegetable intake or unspecified vegetable intake. For all vegetables, across menopausal groups, there was a trend for non-significant decreased risk. There was no consistent evidence for increased fruit or cereal consumption, although there was a trend toward a decreased risk in the few studies identified. There was no significant association between risk and intake of dietary fibre and vegetable fibre.
Fat and energy intake
There was a trend across numerous studies for an increased risk with higher total intake of fat, although the risk increase was non-significant in the majority of studies. There was no consistent evidence of risk between intake of saturated, monounsaturated or polyunsaturated fats and breast cancer. There was no consistent association between total energy intake and risk of breast cancer, although higher intake of energy from fat was associated with borderline increase in risk.
There was a general trend from numerous studies of physical activity decreasing the risk of postmenopausal breast cancer, with risk reduction ranging from 20% to 80% (with far weaker evidence for premenopausal breast cancer). The weak evidence from two studies that increased household activity produced a borderline decrease in risk. The WCRF panel consider there to be suggestive evidence for a decreased risk with increased physical activity.
Body shape and BMI
Among postmenopausal women, increased Body Mass Index (BMI) slightly increased breast cancer risk (5% increased risk per 2kg/m2 increase). Conversely, there was an inverse association among premenopausal women (3% decrease per 2kg/m2 increase), although studies were of widely varying design. There was no association in studies where menopausal age was unspecified.
There was no association between waist circumference and the risk of postmenopausal breast cancer. There also appeared to be no consistent evidence between waist-to-hip ratio and the risk of postmenopausal breast cancer. The studies also varied in design.
Results for the range of individual minerals, vitamins, nutrients and individual foods and their associations with decreased or increased risk of breast cancer, have not been given here, but are in the full report. Many of the other dietary associations were assessed using studies with design methods and types of results that were too different to combine.
Across many of the studies, the associations with decreased or increased cancer risk were non-significant and the WCRF panel say they can make no conclusions on the risk associations with any individual foods, vitamins, minerals, nutrients or dietary patterns.
Are all breast cancer cases related to these risk factors?
Breast cancer has become an increasingly common disease, now affecting around one in nine women. This comprehensive update to the systematic review completed in 2007 has specifically focussed on investigating the associations between breast cancer and lifestyle factors such as diet, alcohol consumption and physical activity.
These types of controllable lifestyle factors can play a role in a woman’s risk of developing breast cancer, (leading to one newspaper coining the phrase 'slob cancer') but it should be remembered that there are a number of largely uncontrollable factors that are known to contribute to the risk of breast cancer. These factors include increased age, close family history of breast cancer, mutations in specific genes, hormone levels (including use of artificial hormones), age at starting and ending periods, number of pregnancies and breastfeeding (WCRF research panel considers there to be convincing evidence of a decreased risk from breastfeeding), prior breast cancer, height, and radiation exposure.
While many of the risk factors for developing breast cancer cannot be easily avoided, the results of this research support the role of healthy lifestyle as a method of preventing breast cancer, specifically adopting a varied, balanced diet, having moderate alcohol consumption and taking regular physical activity.