CHAPEL HILL, NORTH CAROLINA. Breast cancer rates differ greatly between countries. They are 5 times higher in the United States than in Japan and twice as high in France as in neighbouring Spain. Differences in overall fat consumption in these countries have been extensively studied, but no link to breast cancer risk or incidence has been detected so far. A large team of researchers from the Netherlands, Ireland, Spain, Finland, Switzerland, Germany and the United States now report that, while overall fat consumption may not be significant, the make-up of the fats could be. As part of the large EURAMIC Study the researchers investigated the link between the content of polyunsaturated fats in adipose (fat) tissue of postmenopausal women and breast cancer incidence. A total of 291 women with breast cancer and 351 controls were included in the study which involved 5 European medical centers. The women all had samples of adipose tissue taken (from the buttocks) and analyzed to determine the concentration of the main polyunsaturated fatty acids: the omega-3 acids - alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the omega-6 acids - linoleic acid (LA) and its metabolite arachidonic acid (AA).
The study found no significant correlation between omega-3 fatty acid levels and breast cancer incidence, but did find a trend to increasing incidence with increasing levels of omega-6 fatty acids in the adipose tissue samples. The researchers also found a significant association between the ratio of EPA and DHA to LA levels and breast cancer incidence in 4 out of 5 of the medical centers involved in the study. Pooling all results showed that women with the highest ratio had a 35% lower breast cancer incidence than women with the lowest ratio. In other words, women with a relatively high adipose tissue level of EPA and DHA (the main components of fish oils) and a relatively low level of LA and its metabolites had a lower breast cancer risk. The researchers note that LA (linoleic acid) is the precursor of certain eicosanoids which may promote tumour growth. EPA and DHA may also, on their own, inhibit tumour growth because they inhibit the production of these harmful compounds. The researchers also point out that several epidemiological studies have found an inverse correlation between fish consumption and breast cancer incidence and urge further studies to determine the relationship between the dietary intake of specific fatty acids and breast cancer risk.
Simonsen, Neal, et al. Adipose tissue omega-3 and omega-6 fatty acid content and breast cancer in the EURAMIC Study. American Journal of Epidemiology, Vol. 147, No. 4, 1998, pp. 342-52.
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