The effect of coffee is related to estrogens, female sex hormones. Certain metabolic products of these hormones are known to be carcinogenic, and various components of coffee can alter the metabolism so that a woman acquires a better configuration of various estrogens. What’s more, coffee contains caffeine, which also hampers the growth of cancer cells.
The cancer researcher Helena Jernström and her associates have studied the coffee-drinking habits of nearly 460 breast cancer patients being treated in Lund. The results show that the effect of coffee varies depending on which variant the women have of a gene called CYP1A2, which codes for an enzyme that metabolizes both estrogen and coffee. Half of the women had a variant called A/A, while the others had either A/C or C/C.
“Those women who had one of the C variants, and who had drunk at least three cups of coffee a day, developed breast cancer considerably more seldom than women with the A/A variant with the same coffee consumption. Their cancer risk was only two thirds of that of the other women.
A/A women who had drunk two or more cups of coffee a day received more ambiguous help from their coffee consumption. On the one hand, their cancer appeared considerably later than among women who had seldom or never drunk coffee at a mean age of 58 years instead of 48 years, unless they had taken hormone replacement therapy for menopausal symptoms, says Helena Jernström.. On the other hand, nearly 15 percent of these women had estrogen-insensitive (ER negative) tumors, which are more difficult to treat.
“The majority nevertheless had estrogen-sensitive and more readily treated tumors. And women who develop breast cancer at a higher age often do better than those who get it earlier in life,” says Helena Jernström.
She stresses, however, that it is too early to make any dietary recommendations regarding coffee consumption.
“This is new information that needs to be corroborated in other studies before we can issue any recommendations. If coffee does in fact provide some protection against breast cancer, then women in such a coffee-drinking country as Sweden ought to have fewer cases of cancer than other countries. This is also the case, at least compared with the U.S. There the proportion of breast cancer cases in the population is considerably higher, and there people drink both more decaffeinated coffee and less coffee in general.”
These research findings are published in the journal Cancer Epidemiology, Biomarkers and Prevention, with doctoral student Erika Bågeman as lead author.