One of the causes of breast cancer may be inflammation triggered by harmful bacteria say researchers.
Scientists say their idea- as yet unproven – is supported by the available evidence, which is that bacterial induced inflammation is linked to cancer.
The paper in the journal Medical Hypotheses is by Lancaster University medical student Auday Marwaha, Professor Jim Morris from the University Hospitals of Morecambe Bay NHS Trust and Dr. Rachael Rigby from Lancaster University’s Faculty of Health and Medicine.
The researchers say that: “There is a simple, inexpensive potential preventive remedy; which is for women to consume natural yoghurt on a daily basis.”
Yoghurt contains beneficial lactose fermenting bacteria commonly found in milk, similar to the bacteria – or microflora- found in the breasts of mothers who have breastfed.
Dr. Rigby said: “We now know that breast milk is not sterile and that lactation alters the microflora of the breast.
“Lactose fermenting bacteria are commonly found in milk and are likely to occupy the breast ducts of women during lactation and for an unknown period after lactation.”
Their suggestion is that this lactose fermenting bacteria in the breast is protective because each year of breast feeding reduces the risk of breast cancer by 4.3%.
Several other studies have shown that the consumption of yoghurt is associated with a reduction in the risk of breast cancer, which the researchers suggest may be due to the displacement of harmful bacteria by beneficial bacteria.
There are approximately 10 billion bacterial cells in the human body and while most are harmless, some bacteria create toxins which trigger inflammation in the body.
Chronic inflammation destroys the harmful germs but it also damages the body. One of the most common inflammatory conditions is gum disease or periodontitis which has already been linked to oral, oesophageal, colonic, pancreatic, prostatic and breast cancer.
The researchers conclude that: “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.”
Breast cancer is the most common cancer type in women worldwide and is the main cause of cancer mortality in females in the world.[1,2] Both breast cancer incidence and mortality rates have been increasing over the past 30 years for our limited understanding of breast cancer.[3]
The incidence of breast cancer is influenced by many factors such as exogenous hormone intake, diet, and alcohol. The association between dairy intake and breast risk has been analyzed in many epidemiological studies. A previous meta-analysis of 10 studies published from 1981 to 1990 reported a modest increase in breast cancer risk with higher milk consumption.[4]
However, inverse results were found in some recent studies.[5–7] In addition, another review including 36 case-control and 10 cohort studies which analyzed the relationship of milk and milk produces intakes and breast cancer suggested that the epidemiologic evidence does not support a significant relevance of milk or milk products and breast cancer.[8]
Therefore, an available data analysis is needed to provide consistent evidence for an association between milk and milk products and breast cancer risk. The purpose of this study is to assess the connection of intakes of milk and milk products (yogurt) and risk of breast cancer by a meta-analysis of case-control studies.
This analysis was based on separately ingredients of milk, including low-fat/skim milk, whole milk, and yogurt. We based on the previous meta-analysis and extend more case-control studies to identify the relationship of milk or milk products intakes with breast cancer incidence.
Discussion
The published epidemiologic data do not provide consistent evidence for an association between the consumption of milk or milk products and breast cancer risk. However, among these data many factors must be considered.
Moreover, assessment of dietary factor in relation to cancer risk is very difficult and affected by many potential biases. Several methods used in epidemiologic studies, such as food frequency questionnaires and diet records or food diaries, have shown only moderate reliability, and some misclassification of intake is also unavoidable.[18,19]
Therefore, different dietary assessment methods may produce different results. It is generally believed that most dietary factors have relatively small effects on cancer risk and the inevitable misclassification of dietary variables increases the difficulty of detection in risk associated with consumption of milk products.
Consistently, in our meta-analysis no associations with breast cancer risk were identified for intake of low-fat/skim milk, whole milk, and yogurt. Another challenge when evaluating milk and milk products in relation to breast cancer risk is the correlation among nutrients in diet.
Persons with high consumption of milk products may likely to consume large amounts of meat or other high fat foods that could also contribute to an increased risk of breast cancer.[20] Although total energy intake is controlled for, it also difficult to completely separate the effects of milk intake from that of other dietary factors, including intake of various types of fat. Once again, it may be difficult to separate the effects of dairy products from those of other nutrients that alter breast cancer risk.
In addition, average intake varies should be considered between different populations such as a level of consumption that is defined as “low” in one population might be considered “high” in another population. For instance, in a Japanese study, daily intake of milk or milk products was identified as highest exposure category.[21] While, in a study conducted in the United States, the reference category of the lowest exposure level was reported consuming 1 serving/d and the highest level was reported >3 servings/d.[6]
In some cases, the investigators did not report the level of consumption within each quantile, which made it impossible to compare effects at similar levels of consumption across studies. Besides the challenges that are common to many studies of nutritional epidemiology, there are specific challenges related to evaluating milk products. A main hypothesis suggesting that dairy products may reduce breast cancer risk is based on vitamin D content of these products. In the United State, most manufacturers add vitamin D to many products, including milk and margarine. These differences suggest that studies from countries with different regulations and practices regarding vitamin D fortification are not strictly comparable.
If vitamin D is the component of milk products that influences breast cancer risk, comparisons should take into account not only the milk products but also the level of vitamin D in mike products. Generally, the epidemiology studies reviewed do not provide consistent evidence for an association between milk product consumption and breast cancer risk. In addition, some studies also suggest that certain types of fat, growth factors, or environmental contaminants found in milk could increase risk of breast cancer.
Another important question is the cow received bovine growth hormone thus potentially increasing insulin-like growth factors-1 levels in the milk which could in turn stimulate malignant cells to grow more rapidly.[22] The data should analyze whether the milk was derived from cow’s receiving bovine growth hormone. We reviewed all the source of milk in those studies, but those studies did not mention sources of milk, and did not analyze the composition of milk.
Therefore, additional studies that identify the association with certain hormonal and environmental factors may help to further understand the relationship of milk products and breast cancer risk. In conclusion, although several interesting hypotheses link milk product and breast cancer, the available epidemiologic evidence does not support a strong association between the milk/milk products and breast cancer risk.
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More information: A.K. Marwaha et al, Hypothesis: Bacterial induced inflammation disrupts the orderly progression of the stem cell hierarchy and has a role in the pathogenesis of breast cancer, Medical Hypotheses (2019). DOI: 10.1016/j.mehy.2019.109530
