Elsevier

The Lancet

Volume 362, Issue 9379, 19 July 2003, Pages 185-191
The Lancet

Articles
Mortality in relation to oral contraceptive use and cigarette smoking

https://doi.org/10.1016/S0140-6736(03)13907-4Get rights and content

Summary

Background

As part of the Oxford Family Planning Association study, we compared mortality in relation to oral contraceptive use and smoking to highlight the differences between them from the perspective of public health.

Methods

The study consisted of 17 032 women, aged 25–39 years at entry, recruited between May 1, 1968, and July 31, 1974, who had used oral contraceptives, a diaphragm, or an intrauterine device. We assessed mortality from follow-up data recorded until Dec 31, 2000. The analysis is based on woman-years of observation.

Findings

We analysed 889 deaths. Women who had ever used oral contraceptives had increased mortality from cervical cancer (rate ratio 7·2, 95% CI 1·1–303), and decreased mortality from other uterine (0·2, 0·0–0·8) and ovarian cancers (0·4, 0·2–0·7). Oral contraceptives had some adverse effect on deaths from ischaemic heart disease in women who smoked 15 or more cigarettes per day. For all causes of mortality, the rate ratio for death in women who ever used oral contraceptives was 0·89 (95% CI 0·77–1·02). By contrast, this rate ratio was 1·24 (1·03–1·49) in those who smoked one to 14 cigarettes per day, and 2·14 (1·81–2·53) in those who smoked 15 or more cigarettes per day.

Interpretation

There was no harmful effect of oral contraceptive use on overall mortality. By contrast, death from all causes was more than twice as high in smokers of 15 or more cigarettes a day as in non-smokers. The harmful effect was already apparent in women aged 35–44 years.

Introduction

Patterns of mortality in the Oxford Family Planning Association (Oxford FPA) contraceptive investigation have been reported previously,1, 2, 3, 4 most recently in 1989,4 by which time 238 women had died. We present our findings until Dec 31, 2000, based on analysis of 889 deaths. We examined mortality associated with oral contraceptive use and cigarette smoking. In our view, this issue is of public health importance because both use of such contraceptives and smoking are common in women of childbearing age and, arguably, at least as much negative publicity exists about oral contraceptive use as about smoking. Our results should enable direct comparisons between the two exposures that were analysed with information from the same database.

Section snippets

Study population

Methods used in the study have been described elsewhere.1 17 032 women were recruited from 17 family planning clinics in England and Scotland between Jan 1, 1968 and Dec 31, 1974. To be eligible, the women had to be aged 25–39 years, married, white, British, willing to cooperate, and have been a user of either the contraceptive pill for at least 5 months, or a diaphragm or an intrauterine device for at least 5 months without previous pill use. At recruitment, women were asked about their date

Preliminary assessment of data

We first compared mortality from oral contraceptive use and that from smoking in women who were active in the study (ie, under individual yearly follow-up) with that in the whole cohort to the end of 2000. The active cohort analysis was based on woman-years of observation from recruitment until (a) emigration (802 women), death (384), or age 45 being reached with less than 8 years of pill use (6041); (b) loss to follow-up or withdrawal of cooperation (1208); or (c) the end of the individual

Discussion

The present analysis is based on a much larger number of deaths (889) than those in our previous reports,1, 2, 3, 4 and considers mortality from smoking and from oral contraceptive use. Although many researchers have described the effects of smoking on mortality in women,6 we are unaware of any who have compared the effects of smoking with those of oral contraceptive use on the basis of data derived from the same study. Furthermore, as far as we are aware, the findings presented here are the

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