Me. Martinez et al., A PROSPECTIVE-STUDY OF REPRODUCTIVE FACTORS, ORAL-CONTRACEPTIVE USE, AND RISK OF COLORECTAL-CANCER, Cancer epidemiology, biomarkers & prevention, 6(1), 1997, pp. 1-5
To explore the roles of reproductive factors and oral contraceptive us
e in the etiology of colorectal cancer, we examined incident cases of
colorectal cancer (n = 501) that occurred during 1,012,280 person-year
s of follow-up between 1980 and 1992 in the Nurses' Health Study. The
women completed mailed, self-administered questionnaires every 2 years
to update information on the risk factors and major medical events, I
n multivariate analysis, the relative risk (RR) of colorectal cancer a
mong women who experienced menarche at age 14 or older was 0.83 (95% c
onfidence interval (CI) = 0.64-1.08) compared with women who had menar
che at age 13; women whose menarche occurred under age 12 were at high
er risk (RR = 1.22; 95% CI = 0.96-1.55, P for trend = 0.01), Compared
with women whose first pregnancy was before age 24, the risk for color
ectal cancer was significantly increased among women whose first pregn
ancy was at age 30 or older (RR = 1.57; 95% CI = 1.15-2.14; P for tren
d = 0.02), No important associations were seen for parity or age at me
nopause. Women who used oral contraceptives for 96 months or longer ha
d a 40% lower risk of developing colorectal cancer (RR = 0.60; 95% CI
= 0.40-0.89; P for trend = 0.02) compared with women who never used or
al contraceptives, These prospective data suggest that a later age at
menarche and use of oral contraceptives may reduce risk of colorectal
cancer, whereas women with a later age at first pregnancy may have a h
igher risk.