Study question: Does moderate alcohol intake affect menstrual cycle characteristics among women in the Danish population?
Summary answer: Levels of alcohol exposure as seen in this study do not substantially affect the menstrual cycle.
What is known already: Animal studies indicate alcohol-induced disruptions of the reproductive system, but previous epidemiological studies addressing the possible association between alcohol intake and the menstrual cycle are sparse.
Study design, size, duration: A cross-sectional study with retrospectively collected data including 82 146 pregnant Danish women in the Danish National Birth Cohort (DNBC) enrolled during the years 1996-2002.
Participants/materials, setting, methods: Information on weekly alcohol consumption and menstrual cycle characteristics before pregnancy was obtained through a computer-assisted telephone interview in pregnancy Week 12-16. The associations between weekly alcohol consumption and menstrual cycle irregularity (≥7 days difference between cycles) and length (short cycle: ≤24 days, long cycle: ≥32 days) were analysed using logistic regression with weekly alcohol intake categorized into abstainers (0 drinks per week), low (0.5-2.0 drinks per week), moderate (2.5-14.0 drinks per week) and high (14.0-86.5 drinks per week). Estimates are given as adjusted odds ratios with 95% confidence intervals.
Main results and the role of chance: The overall participation rate was 60% of the women invited. We found that a high weekly alcohol consumption was not associated with menstrual cycle disturbances. We observed higher odds of irregular and short cycles among abstainers when compared with women with a low weekly alcohol consumption, but found no trend of more cycle disturbances with higher alcohol consumption.
Limitations, reasons for caution: Possible limitations in our study include a risk of selection bias due to the moderate participation rate and the use of retrospective information on alcohol exposure and menstrual cycle characteristics before getting pregnant. The higher odds of irregular and short cycles among abstainers may reflect other health problems in these women rather than an actual effect of alcohol on the menstrual cycle.
Wider implications of the findings: The generalizability of the study results is restricted to women who manage to conceive and women who do not use oral contraceptives within 2 months before getting pregnant. This study suggests that the menstrual cycle is not substantially affected by higher alcohol consumption among the participating women.
Study funding/competing interest(s): Supported by a scholarship from Aarhus University Research Foundation. The Danish National Research Foundation has established the Danish Epidemiology Science Centre that initiated and created the DNBC. The cohort is furthermore a result of a major grant from this Foundation. Additional support for the DNBC is obtained from the Pharmacy Foundation, the Egmont Foundation, the March of Dimes Birth Defects Foundation, the Augustinus Foundation and the Health Foundation. No conflict of interest declared.
Keywords: alcohol drinking; female reproduction; menstrual cycle.