[sfem]

This is the topic that won't die.

There is no proven answer to the question, "Is coffee good or bad for NBE?". Do your own experiment to find out how or if it affects you. If coffee makes you nervous, just stay away from it. Nothing bad will happen to you as a result of avoiding coffee. A reasonable summary of several studies is at http://www.healthyfellow.com/651/coffee-estrogen-link/ :

The June 2009 issue of the journal Cancer examined the relationship between “caffeine, coffee, decaffeinated coffee and tea” and plasma concentrations of various sex hormones in 524 premenopausal and 713 postmenopausal women. In the premenopausal women, caffeine intake was associated with significantly lower levels of estradiol (a form of estrogen). The postmenopausal women demonstrated a positive association between caffeine and coffee intake and SHBG (sex hormone-binding globulin). However, this did not translate into any significant alteration in hormone levels. (4)
The October 2001 edition of the journal Fertility and Sterility investigated the hormonal influence of alcohol, coffee and tobacco in 498 women with ages ranging from 36 – 45 “who were not currently pregnant, breast feeding, or using exogenous hormones”. Coffee consumption of more than 1 cup per day was associated with higher estradiol levels. Up to a 70% increase in “early follicular phase E2 (estradiol)” was found in women consuming over 500 mg of caffeine/day vs. those consuming <100 mg/day. (5)
A 1998 publication in the journal Nutrition and Cancer studied the relationship between caffeine-containing beverages (black tea, coffee, cola, green tea and oolong tea) and serum estradiol and SHBG concentrations in 50 premenopausal women. Specifically, the researchers examined any hormonal alterations occurring on days 11 and 22 of the women’s menstrual cycles. Blood samples and food frequency questionnaires revealed that a higher intake of caffeine correlated to increased SHBG (sex hormone binding globulin). SHBG may inhibit estradiol-induced breast cancer cell growth and spread. Perhaps that’s why the conclusion of the study states that “consumption of caffeine-containing beverages appeared to favorably alter hormone levels associated with the risk of developing breast cancer”. (6,7)
A 1996 study involving 728 postmenopausal women noted “significant inverse associations between caffeine intake and bioavailable testosterone”. Two or more cups of coffee or > 4 cans of caffeinated soda per day was also correlated with higher estrone and SHBG levels. The downside of this examination (“The Rancho Bernardo Study”) is that it didn’t differentiate between coffee and soda intake. (8)
The May 1992 edition of the Annals of Epidemiology reported that “coffee intake, ascertained at the 26th week (of pregnancy), was found to be negatively related to pregnancy E2 (estradiol) levels”. This is believed to be one of the reasons why caffeinated coffee should be avoided during pregnancy as lower estrogen levels have been correlated with lower birth weight. (9,10,11)
There simply haven’t been enough well-designed studies to know with certainty what effect coffee is likely to have on estrogen concentrations in women during varying stages of life. But there is other information available which may assist in forming a more well-rounded perspective on this issue. Hormone replacement therapy (HRT) has been documented as increasing the incidence of breast cancer, endometrial cancer, heart attacks and strokes. If coffee truly provokes significant elevations in estrogen levels, it would seem likely that it too would increase the risk of the same health concerns.