Xenoestrogen levels in milk : bioavailability and relevance as breast cancer risk factors.
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Hormones are key control molecules fundamental to most biochemical functions in the body. The endocrine system is responsible for the synthesis, regulation and secretion of sex hormones into the circulatory system to control target organs, tissue and cells through receptor mediated responses. The balance between two key steroid hormones, 17-estradiol (E2) and testosterone, the female and male sex hormones respectively is critical for fetal growth and development. A disruption to this tightly regulated system may lead to implications such as early onset of puberty in girls, decreased sperm count, and increased risk of breast cancer in postmenopausal women. Xenoestrogens (from the Greek xenos meaning stranger) are foreign compounds that have structural similarities to E2 and although the binding site for E2 is very specific, they have the ability to bind to estrogen receptors (ERs) but not as well, resulting in less of a biological response. Each xenoestrogen has a different affinity for ERs resulting in various cellular responses – also known as estrogenicity.
There has been an increasing interest in the concentration of xenoestrogens in cow’s milk due to the possible effects consuming these compounds may have on the population. Here, this study utilised and evaluated a method for extracting endogenous estrogens (E2) and xenoestrogens (17-ethinyl estradiol; EE2, formononetin, genistein, daidzein, equol, bisphenol A; BPA and zearalenone) from cow’s milk. The performance of this method was acceptable with recoveries ranging from 62% (BPA) to 95% (EE2), limits of determination ranging from 0.0025 mg/L (daidzein) to 0.1 mg/L (E2) and limits of quantification of similar values ranging from 0.05 mg/l (zearalenone) to 1 mg/L (E2).
During the duration of the current study articles were published citing tests that found trace amounts of the herbicide, glyphosate, in Ben and Jerry’s ice cream in the United Kingdom. These findings and published literature on glyphosates ability to induce human breast cancer cell growth lead to question the presence of glyphosate in New Zealand cow’s milk. A previously accepted extraction method was used to determine the presence of glyphosate, due to the low concentrations published, direct inject probe mass spectroscopy was utilised. In sampled New Zealand cow’s milk from the Canterbury region (n = 5), no mass ion consistent with glyphosate was identified.
This extraction method was used to assess the safety of New Zealand cow’s milk in an estrogenic mimic context. In sampled New Zealand cow’s milk from the Canterbury region (n = 30), BPA was identified in 9 samples at concentrations ranging from 0.012 mg/L to 0.066 mg/L, daidzein was identified in 1 sample at a concentration of 0.026 mg/L and genistein was identified in 1 sample after treatment with sulfatase/- glucuronidase at a concentration of 0.062 mg/L. Based on the values from this study a person who drinks the New Zealand population’s average amount of milk (133 mL) would not be exposed to concentrations of each compound that exceeds their acceptable daily intakes (BPA, 0.05 mg/kg bw; genistein, 1.5 x 10-4 mg/kg bw; and daidzein no data (based on structural similarities to genistein it was assumed daidzein would have a similar acceptable daily intake value)). In New Zealand, cow’s milk is an essential part of the diet providing key minerals and nutrients, the findings in the present study suggest that New Zealand cow’s milk is safe. However, future studies could investigate whether more sensitive analytical techniques could detect other possible xenoestrogens at lower concentrations compared to high performance liquid chromatography – diode array detector (HPLC-DAD).