Sorting through the studies: breast cancer and diet

Breast cancer is the most common cancer diagnosed among Canadian women, accounting for about 30 per cent of all new cancer cases each year. One in 25 Canadian women will die from this disease and researchers are still not certain of the direct cause.

However, for the one in nine Canadian women who will develop breast cancer in their lifetime, nutrition research continues to find answers in the area of prevention and protection and also in tumor reduction.

Dr. Elaine Hardman, a researcher at Marshall's Joan Edward School of Medicine, says "we are beginning to understand that diet probably contributes to one-third to two thirds of all cancer that develops."

Breast tumour reduction

Medicine is increasingly looking at dietary changes as a way to reduce cancer tumours. In a current issue of Nutrition and Cancer, for example, it's reported that walnut consumption suppressed tumour growth in animals compared to those following a typical American diet.

Researchers found that a diet rich in omega-3 fatty acids had an effect on cancer growth, as tumours took twice as long to double in size as tumours in the control group.

When animals were fed a diet in which 18.5 per cent of the daily calories came from walnuts, the equivalent of two servings for humans, the growth rate of the tumours was dramatically reduced.

Researchers concluded that walnuts have at least three components that could account for their cancer-slowing effect: they are high in omega-3 fatty acids, but also include antioxidants and components called phytosterols.

From this research, Hardman suggests that, on the whole, individuals need to take in more of their fat calories from fats rich in omega-3 fatty acids and fewer fat calories from saturated fat or foods high in omega-6 fatty acids (corn and safflower oils).

Increasing your intake of omega-3 fatty-acid rich food such as walnuts, fish, canola and flaxseed oils, and/or omega-3 functional food is a good thing to do for breast cancer protection.

Breast cancer protection

Recently, in the American Journal of Epidemiology, it was shown that increased intake of vitamin D from the diet and from sunlight may reduce the risk of breast cancer by more than 20 percent.

Canadian researchers analyzed the vitamin-D intakes of 759 women with breast cancer and compared this to the vitamin-D intakes of 1,136 healthy controls.

Increased intakes of the sunshine vitamin were associated with a 24 per cent reduction in the risk of developing estrogen receptor and progesterone receptor positive tumours.

Moreover, increased intakes of vitamin D were also associated with 26 and 21 per cent reductions in the risk of receptor negative and mixed receptor tumours.

In addition, an evaluation of the data from the Women's Health Study examined calcium and vitamin D intake in relation to incidence of breast cancer in 10,578 pre-menopausal and 20,909 post-menopausal women.

Over an average of 10 years of follow-up, higher intakes of vitamin D and calcium were associated with a lower risk for pre-menopausal breast cancer.

Increasing your intake of vitamin D rich foods such as salmon, tuna, sardines, milk, margarine and vitamin D functional foods and/or taking a multivitamin with vitamin D is a good thing to do for breast cancer prevention.

Some types of breast cancer may also be related to the interaction between low folate intake and alcohol consumption.

An analysis of the Nurses Health Study reported the risk of breast cancer among post-menopausal females with low dietary folate intakes increased with any level of alcohol consumed.

In the American Cancer Society Cancer Prevention Study, the risk of breast cancer was 25 per cent higher with alcohol consumption.

Epidemiologic studies support a positive association between a high intake of dietary folate and reduced breast cancer risk.

Increasing your intake of folic-rich foods such as green, leafy vegetables, asparagus, fortified breakfast cereals and orange juice is a good thing to do for breast cancer prevention.

In some epidemiological studies, the dietary soy intake of 5 grams of soy protein per day is associated with a modest protective effect in reducing the risk of developing breast cancer in both Western and Asian women.

Menopausal status and body mass index may alter the effects of soy on breast cancer risk, but it is difficult to conclude from the existing research. At this time, there is a lack of human intervention studies that directly examine the effects of soy on breast cancer risk.

Bottom Line
- Consume omega-3 fatty acid rich foods daily.
- Eat at least 7 to 8 servings of vegetables and fruits each day. Include at least one dark green vegetable daily.
- Take a multivitamin with vitamin D each day.
- Maintain a healthy weight and do physical activity daily. Enjoy 30 to 60 minutes of moderate activity each and every day.

--- Samara Felesky-Hunt

Samara Felesky-Hunt is a registered dietitian at The Downtown Sports Clinics in Calgary. Her column appears weekly in the Herald. She can be reached at dietitian-online.com

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