Tobacco and Public Health - TCSC Indonesia

536
ENDOMETRIAL CANCER
results to those that did not, suggesting that BMI is not a strong confounding variable
in this association.
Two studies examined the association between cigarette smoking and blood
estrogen levels after randomization of women to groups receiving either estradiol or
placebo (Table 31.5) (Jensen and Christiansen 1988; Cassidenti et al. 1990). In a
small study of 25 postmenopausal women (Cassidenti et al. 1990), unbound estradiol
was significantly lower among smokers than nonsmokers both at baseline and
shortly after taking micronized estradiol orally. No important differences were
observed between smokers and nonsmokers in serum levels of either estrone or bound
estradiol. In contrast, a study in which 110 postmenopausal women were randomized
to take hormones (either orally or percutaneously) or a placebo (Jensen and
Christiansen 1988) found that smokers had lower levels of both estrone and bound
estradiol than nonsmokers after oral (but not percutaneous) hormone treatment for
at least one year (levels of free estrogens were not examined). These results indicate
that smoking might affect the absorption or metabolism of hormones used in
replacement therapy.
Smoking and blood sex-hormone binding globulin
(SHBG) levels
Of the five studies that have examined the association between cigarette smoking and
serum (Lapidus et al. 1986; Cassidenti et al. 1992; Law et al. 1997) or plasma (Khaw
et al. 1988; Longcope and Johnston 1988) SHBG, none found any clear association.
However, one of these studies (Khaw et al. 1988) found an inverse association between
smoking and the ratio of bound estradiol to SHBG, a measure of estrogen activity.
In this context, it is interesting to note that Cassidenti et al. (1990) found unbound
(but not SHBG-bound) estradiol significantly lower among smokers than nonsmokers
both at baseline and after taking oral estradiol, suggesting an increased SHBG-binding
capacity in the women who smoked.
Smoking and blood androgen levels
In postmenopausal women, androgens are the major source of estrone, converted
through an aromatization process in fat deposits. Thus, adiposity is positively correlated
with estrogen levels in postmenopausal women. Of the nine studies that examined
blood levels of androstenedione in smokers (Friedman et al. 1987; Khaw et al. 1988;
Longcope and Johnston 1988; Cauley et al. 1989; Slemenda et al. 1989; Schlemmer
et al. 1990; Cassidenti et al. 1992; Austin et al. 1993; Law et al. 1997), all found higher
circulating levels among current than never or former smokers (Table 31.5). However,
these same studies did not show clear variation in blood estrone levels by smoking
status, perhaps suggesting a reduced conversion of androstenedione to estrone among
smokers. Of the five studies that have examined cigarette smoking and DHEAS levels,
three (Friedman et al. 1987; Khaw et al. 1988; Cassidenti et al. 1992) found increased