Impact of cows’ milk estrogen on cancer risk.

Discipline: dairy &health; Key words: oestrogens, dairy products, endometrial cancer, nutrients, meta-analysis. 

Oestrogens have been implicated in cancer at sites where hormones are active, such as the breast, ovaries, endometrium and prostate. Because cow milk contains oestrogens, there is the perception, supported by some authors, that oestrogen consumption may contribute to the risk of cancer at these sites. In a review by Dr P.W. Parodi, he argued that these reports do not recognize the complex mechanisms which these sites possess to regulate oestrogen levels. Hormone-sensitive and many other cells contain all the necessary enzymes for synthesis of the required oestrogens from abundant precursors in the body and for inactivation of unwanted ones. His review also showed that oestrogens from dairy products is extensively inactivated in the gastrointestinal tract and only about 5% survives the first pass to the liver. This implies that for a normal daily dairy product intake the supply would only be about 0.25% of the FAO/WHO upper acceptable daily intake of oestrogens. Accordingly, in his review of the literature, the available evidence does not suggest an association between dairy product consumption and risk of cancer of the breast, ovaries and endometrium. Dr Parodi’s review was published in the International Dairy Journal, Volume 22 of 2012, page 3 to14, the title being: Impact of cows’ milk estrogen on cancer risk. 

However, this topic remains on the research agenda, and therefore recently a study was conducted by Dr X. Li and colleagues which was published in the journal “Nutrients” Volume 10, number 25 of 2018 [doi:10.3390/nu10010025], the title being: Dairy Products Intake and Endometrial Cancer Risk: A Meta-Analysis of Observational Studies.

Their study aimed to evaluate the correlation (if any) between the intake of dairy products and the risk of endometrial cancer. They used extensive data bases in a meta-analysis for the purpose, amongst others using observational data of more than 400 000 subjects. Two cohort and 16 case-control studies were included in the analysis. No significant association was observed between endometrial cancer risk and the intake of total dairy products, milk, or cheese for the highest versus the lowest exposure category. One cohort study reported a positive association of butter intake with endometrial cancer risk, but the p-value of 0.31 was clearly not significant. Interestingly, there was a significant negative association of dairy products intake and endometrial cancer risk among women with a higher body mass index (p = 0.002), suggesting that dairy product intake in this category could be preventative. The authors suggested that future work should be well-designed, amongst others stratifying the statistical analyses by risk factors including body mass index, when exploring the association of dairy products intake with endometrial cancer risk.

In conclusion, this recent study (2018) by Li and co-workers corresponds with the earlier (2012) review of Parodi that there is no evidence of a relationship between dairy product intake and primary cancer types.