Breast Cancer: A Little Bit of Yogurt Seems to Go a Long Way

This past October, I wrote about probiotic use in breast cancer.  If you remember, that paper concluded that what few in vitro and in vivo studies we have look promising.  One piece of research mentioned in that paper is particularly pertinent to today’s post:  “One Japanese study asked 306 women with BC, and 662 women without, about their diets, lifestyles and other risk factors and found that regular and long-term consumption of L. casei Shirota (found in Yakult yogurt, and which I have written about before – for example,  here ) was ‘…significantly associated with decreased BC risk in Japanese women.’”

One of the big biome stories of the week:  another paper just came out that once again, points out the fact that eating yogurt is highly associated with a decrease in breast cancer risk.[i] This paper, out of Lancaster University in the UK, suggests the following hypothesis:  “…the mechanism proposed in this article is that the bacteria which cause cancer induce inflammation which leads to the destruction of the stem cells…”  This leads to “genetic instability” and mutations within the breast cell DNA.

The authors point out that breast ducts are far from sterile.  Pregnancy and lactation are known to decrease the risk of breast cancer fairly dramatically:  “Following pregnancy and lactation, they will have a flora which is dominated by lactose fermenting bacteria.  This appears to be protective against the development of cancer.”  However, bacteria from other areas of the body, where pathogenic bacteria may be present, can travel via the blood stream and can cause dysbiosis in a wide variety of other tissues.  For example, periodontitis, which is inflammation of the gums caused by bad bacteria, is highly associated with a wide variety of other illnesses including senility, atherosclerosis, rheumatoid arthritis and cancer (including of the gastrointestinal tract, breast, prostate and pancreas).  It is likely that “…organisms of the mouth are carried through the blood to distant sites and cause direct tissue destruction and inflammation.  In the breast we envisage that the pathogenic bacteria directly damage epithelial cells…”

The good news:  eating daily yogurt seems to make a very statistically significant difference in breast cancer risk.  One meta-analysis (which has been replicated), which looked at thousands and thousands of cases, showed that “…high and modest dairy consumption significantly reduce the risk of breast cancer compared with low diary consumption.”  Further analysis showed that the effect forms of dairy were low fat dairy and yogurt – not other forms, like fluid milk.  And the amount:  about 2-3 cups of these forms of dairy per day (400-600 grams).

In a press release about the study, one of the authors states, “…The stem cells which divide to replenish the lining of the breast ducts are influenced by the microflora, and certain components of the microflora have been shown in other organs, such as the colon and stomach, to increase the risk of cancer development. Therefore, a similar scenario is likely to be occurring in the breast, whereby resident microflora impact on stem cell division and influence cancer risk.”[ii]

The conclusion:  “…there is a simple, inexpensive potential preventive remedy; which is for women to consume natural yogurt on a daily basis…”

A little bit of good news, on the things-you-can-do-now front!


[i] Marwaha, AK, Morris, JA, Rigby, RJ. Hypothesis: bacterial induced inflammation disrupts the orderly progression of the stem cell hierarchy and has a role in the pathogenesis of breast cancer. Medical Hypothesis. 2020; 136:109530. doi:10.1016/j.mehy.2019.109530.


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