The level of endogenous DNA damage in lymphocytes isolated from blood is associated with the fluctuation of 17β-estradiol concentration in the follicular phase of healthy young women

al., 1999), caused by environmental toxins or drug administration (Abd-Allah et al., 1999; Puhakka et al., 2002) and some nutritional deficiencies (Giovannelli et al., 2002; Szete et al., 2002; White et al., 2002; Kapiszewska et al., 2005a). It was shown that the comet assay used to study single/double strand breaks and oxidative modifications in the DNA bases was sensitive enough to detect also alterations in the antioxidant status in the body induced by nutritional supplements or vitamins (Betancourt et al., 1995; Anderson et al., 1997; Anderson, 2001; Beani, 2001). The endogenous DNA damage analyzed in lymphocytes is very o en used as a biomarker of the oxidative stress in the human body (Porrini et al., 2002; Szeto et al., 2002; Wolf et al., 2002; Mayne, 2003). Constant exposure of lymphocytes to substances transported by circulation make them very useful and reliable as a diagnostic tool. Taking all of the above into account, it is reasonable to expect that if circulating estrogens and their metabolites enhance free radical production, then their detrimental effect can be manifested in DNA modification also in lymphocytes. We showed recently that Communication