Dietary factors and breast cancer

Because of the difference in breast cancer rates in different parts of the world, scientists have been looking into whether eating phyto oestrogens, and particularly soya, could affect the risk of getting breast cancer.  There is also research into whether soya can alter risk of breast cancer coming back in women who already have the disease, but this is a different area of research. The information here is about risk for women who do not already have breast cancer.

Phyto oestrogens are chemicals found in plants (phyto means 'plant'). So they can also be called plant oestrogens.  They have a similar structure to the female sex hormone oestrogen. There are different types of phyto oestrogens. Some are found in soya bean products (isoflavones). Others are found in the fibre of whole grains, fruit, vegetables and flax seed (lignans). Milk may also contain phyto oestrogens, but this depends on what the cows have been eating!   

Lignans are the main type of phyto oestrogens in the Western diet. Research into the effect of lignans on breast cancer risk was conflicting. So in 2009 researchers looked at all the studies that had been done. They found that in women who had had their menopause, high levels of lignin in the diet slightly reduced their breast cancer risk. It had no effect for premenopausal women though. But the researchers say that we need more studies to confirm these results.

A joint study reported in July 2002, produced by Cancer Research UK, the National Cancer Institute of the USA and the National University of Singapore. It found that women with a diet high in soya had less dense breast tissue than women with low soya diets. Higher density of breast tissue has been linked to a higher risk of breast cancer. This is the first study to directly link eating soya with an effect on breast tissue. Combining the results of lots of separate studies (a meta analysis) showed that Asian women who eat the highest amounts of soy foods had a lower risk of breast cancer. In other parts of the world, most women do not eat enough soy to reduce their risk of breast cancer,

Further research has since seemed to show that that women whose diets are high in soya phyto oestrogens have a lower risk of breast cancer. But we need more research to confirm this. In some studies, eating phyto oestrogens (soya flour and linseed supplements) regularly over several weeks reduced oestrogen levels. One of the active ingredients in soya is isoflavone.  This chemical mimics oestrogen and reduces the effect of human oestrogen in the body. High levels of human oestrogen can increase breast cancer risk.

Obese women who have had their menopause are more likely to get breast cancer. We do not know exactly why this is, although there are some theories. 'Obese' means more than about 25% overweight.  So the upper limit of normal weight for your height, plus a quarter again.

The increase in cancer risk in obese women may be due to changed hormone levels. Populations of women at higher risk of getting breast cancer are often found to have higher oestrogen levels than populations with lower breast cancer risk. After the menopause, oestrogen is changed into its active form in the body fat. Obese postmenopausal women could have higher oestrogen levels simply because they have more body fat.  So that could mean a higher risk of breast cancer.

If you are premenopausal, being overweight can slightly lower the risk of breast cancer. But it increases the risk of other illnesses such as diabetes and heart disease. Look at the section on definite risk factors for breast cancer for more information.

Many things come under the general heading of food additives including

• Preservatives
• Saccharine
• Curatives (used to make bacon, ham, corned beef etc)

There is no research to suggest that food additives increase the risk of breast cancer. Most food additives actually help reduce the risk of cancer, for example, by stopping food going mouldy .

There has been concern about saccharine in the past. But it has not been shown to cause cancers in people, only in laboratory animals. Even so, in the food industry other sweeteners have mostly replaced it.

We have included this because it gets press coverage from time to time and people become anxious about it. There is no reliable evidence that pesticides cause breast cancer. Most studies have found that they don't increase cancer risk. But an American report in 2008 found that exposure to the pesticide DDT (dichlorodiphenyltrichloroethane) early in life may increase breast cancer risk. DDT is no longer used but it was widely used from the 1950s to the 1970s.

We know that drinking alcohol increases breast cancer risk. Recent research showed that the more we drink, the higher the increase in risk. There is detailed information about alcohol and breast cancer risk in this section.

Why not keep a check on your alcohol intake for a week? Find out if your drinking is within the recommended safe levels for your health. Women should drink a maximum of 14 units per week and men 21 units per week. A unit is one small glass of wine, a measure of spirits or half a pint of average strength beer.

We have included information about coffee because it gets press coverage from time to time. A lot of research has looked into coffee drinking and cancer risk. Breast cancer is one of the cancers investigated. But there is no research evidence to show that coffee  increases breast cancer risk.