What is less known, and studied, is that friendly microorganisms found within fermented milk products could potentially reduce the incidence of tumors. For instance, in the colon, Lactobacilli can produce compounds that could inhibit the local activity of beta-glucuronidase and nitroreductase, two enzymes involved in carcinogenesis.

But can compounds secreted by friendly microorganisms also influence tumor formation in sites distant than the gastrointestinal system? Some epidemiological studies do point in that direction. At least two studies have indicated a reduced risk of breast cancer in women who consume fermented milk products (Veer, Le).

Researchers at the National Institute for the Study and Cure of Cancers in Milan, Italy, set out to evaluate the role of these friendly microorganisms on MCF7 breast cancer cells in vitro. Five different bacterial strains were used: Bifidobacterium infantis, Bifidobacterium bifidum, Bifidobacterium animalis, Lactobacillus acidophilus, and Lactobacillus paracasei. All the bacterial strains were grown in reconstituted skim milk. The results showed a growth inhibition induced by all the fermented milks. However, B infantis and L acidophilus were the most effective. Interestingly, the anti-proliferative effect was not related to the presence of bacteria in fermented milk, and neither whole milk, nor its main fractions (lactalbumin or B-lactoglobulin fractions). Something else was influencing the inhibition of the breast cancer cells. The researchers conclude, "Our finding suggest the presence of an ex novo soluble compound produced by lactic acid bacteria during milk fermentation or the microbial transformation of some milk components in a biologically active form. Although the mechanism of the antitumor activity is not clear, the present study suggests the potentiality offered by fermented milk as producers of compounds with anti-proliferative activity useful in the prevention and therapy of solid tumors like breast cancer."

Biffi A, Coradini D, Larsen R, Riva L, Di Fronzo G. Antiproliferative effect of fermented milk on the growth of a human breast cancer cell line. Nutrition and Cancer 28(1):93-99, 1997.

Le MG, Moulton LH, Hill C, Kramer A. Consumption of dairy products and alcohol in a case control study of breast cancer. JNCI 77:633-636, 1986.

Veer P, Dekker JM, Lamars JW, et al. Consumption of fermented milk products and breast cancer: a case-control study in The Netherlands. Cancer Res 49:4020-4023, 1989.

Comments: I've always thought of the positive effects of friendly microorganisms in the gut to be active mostly locally. It's interesting to speculate that perhaps there are chemicals produced by these organisms that could be released into the local gastrointestinal circulation and then transported to the systemic circulation. These compounds could then play a role in many types of tissues of the body. I guess the next scientific step would be to isolate compounds made by these microorganisms directly in the systemic circulation.

In the meantime, consuming yogurt, kefir, or other fermented milk products would seem reasonable. If a person does not wish to consume fermented products, or does not like their taste, it would seem quite justified to supplement with capsules containing these bacteria.