“Teen drinking among girls increases chance of breast cancer by one third,” The Daily Telegraph reports. A US study found that women who regularly drank during their teens and 20s, before they had children, were more likely to develop breast cancer in later life.
The study was looking at a particular point in a woman’s life – the period between having her first menstrual period (menarche) and her first pregnancy. This study was looking at whether alcohol consumption at this time increased the risk of benign breast disease (BBD) and breast cancer. BBD refers to a group of conditions that can cause non-cancerous lumps in the breast tissue. A type of BBD called proliferative BBD can increase breast cancer risk.
They did find that there was an association between alcohol consumption during this time and an increase in the risk of BBD and breast cancer. The association seems to be dose-dependent – the more alcohol women consumed, the greater the risk.
A longer interval between a woman’s first period and first pregnancy also appeared to increase risk.
This was a large, well-conducted study and the results are concerning. Alcohol is already known to be a risk factor for breast cancer and heavy drinking at a young age has other health risks.
Experts advise that women of all ages consider reducing alcohol consumption to reduce the risk of breast cancer.
Where did the story come from?
The study was carried out by researchers from Washington University School of Medicine, Brigham and Women's Hospital, Harvard Medical School, Beth Israel Deaconess Medical Center and Harvard School of Public Health. It was funded by the National Cancer Institute in the US.
It was covered widely in the media and reporting was generally accurate.
Both the Daily Mail and The Daily Telegraph calculated that one glass of wine a day through the teenage years would increase the risk of breast cancer by a third. A large glass of wine is three units of alcohol, which equals 8g of pure alcohol. Going by the findings in this research, this calculation is roughly correct.
What kind of research was this?
This was a prospective cohort study. The study aimed to find out whether drinking in the time between a woman’s first period and a first pregnancy increased the risk of breast cancer and of proliferative benign breast disease (BBD). This is a group of conditions where some breast cells grow too quickly, resulting in breast lumps. This, in turn, leads to increased breast cancer risk.
Cohort studies enable researchers to follow large groups of people for many years, to look at links between lifestyle and health, but they cannot prove that one thing (alcohol) causes another (breast cancer).
The authors point out that other, non-cohort studies, have found a causal relationship between alcohol and breast cancer risk.
Breast tissue undergoes rapid proliferation between the first period (the menarche) and first pregnancy, so may be particularly vulnerable to damaging substances during this time. The researchers also say that alcohol consumption in late adolescence and early adulthood is associated with increased risk of proliferative benign breast disease (BBD), a known risk marker for breast cancer.
What did the research involve?
The researchers used data from 91,005 women aged 25 to 44, who took part in a large US study looking at their health and lifestyle. The study began in 1989 and followed participants until 2009. For this particular research, the women had no cancer history and had carried a pregnancy to at least six months’ gestation. Information was also available on their age at first period and age at first pregnancy.
In the first year of the study, the women completed a mailed questionnaire about their medical history, reproductive history and lifestyles. Follow-up questionnaires mailed every two years updated this information.
Participants were asked in 1989 about their alcohol consumption in four age periods – when they were 15–17, 18–22, 23–30 and 31–40 years.
They were asked about the total number of drinks of alcohol (including beer, wine and spirits) consumed at these different ages. There were nine response categories ranging from “none or less than one drink a month” to “40 or more a week”.
One drink was defined as one bottle or can of beer, a four-ounce glass of wine or a shot of spirits.
The estimated content of ethanol (alcohol) per alcoholic drink was 12.0g, which corresponds to one and a half units of alcohol.
Participants were asked separately about their alcohol consumption over the previous year for beer, wine and spirits. Total amounts of alcohol consumed were calculated, based on the equivalents of 12.8g of alcohol for regular beer, 11.0g for wine and 14.0g for spirits.
The women’s reports of their current drinking were updated in 1991, 1995, 1999 and 2003. During the follow-up, participants were asked about their alcohol consumption separately for regular and light beer, red and white wine, and spirits.
From this information, researchers calculated the women’s cumulative average alcohol intake between age at their first period and age at their first pregnancy.
The women were followed until 2009 to look at their breast cancer risk. Where women self-reported breast cancer, researchers asked permission to review medical records and pathology reports, which confirmed 99% of self-reported breast cancers. They also searched the national death index.
A subset of 60,093 women who had no history of BBD or cancer in 1991 were followed until 2001 to analyse the risk of proliferative BBD. Researchers reviewed the breast biopsy specimens of women who reported having been diagnosed with BBD. They restricted their analysis of BBD risk to women who had a type called proliferative BBD, since this is a predictor of breast cancer risk.
Researchers analysed the association between the women’s drinking and their risk of proliferative BBD and breast cancer.
The results were adjusted for established risk factors for breast cancer, including:
- body mass index
- menopausal status
- postmenopausal hormone use
- duration of breastfeeding
- number of children
- age at first pregnancy
- family history of breast cancer
They also adjusted the results for the amount women drank after their first pregnancy.
What were the basic results?
Of the 91,005 women who took part, just over one-fifth reported not drinking any alcohol between first period and first pregnancy, while 3.8% reported moderate to high alcohol consumption (15g daily or more), during this time. Between 1989 and 2009, 1,609 women (1.7% of the total) got breast cancer and 970 had proliferative BBD.
The researchers found that alcohol consumption between a woman’s first period and first pregnancy was associated with:
- an 11% increased risk of breast cancer for every 10 grams of alcohol a day (95% confidence interval [CI] 1.00 to 1.23)
- a 16% increased risk of proliferative BBD for every 10g of alcohol a day (95% CI 1.02 to 1.32)
Drinking after a first pregnancy had a similar risk for breast cancer (relative risk [RR] = 1.09 per 10g/day intake; 95% CI 0.96 to 1.23) but not for proliferative BBD. The association between drinking before first pregnancy and a higher risk of abnormal changes to breast tissue (neoplasia) appeared to be stronger in women with longer intervals between their first period and first pregnancy.
How did the researchers interpret the results?
Alcohol consumption before first pregnancy was consistently associated with increased risk of proliferative BBD and breast cancer, say the researchers.
They argue that breast tissue cells are thought to be particularly susceptible to cancer-causing substances as they undergo rapid proliferation during this period.
They estimate that 11,617 cases of breast cancer which would otherwise be diagnosed each year in the United States would not occur “if the persons at risk did not drink alcohol before their first pregnancy”.
Alcohol consumption is already recognised as a risk factor for breast cancer. And this large, well-conducted study seems to confirm that young women between their first period and first pregnancy are particularly susceptible.
One limitation of the study is that the women were asked to recall their drinking habits when they were far younger, which could mean the results are less reliable. Also, other factors called confounders might have affected women’s risk of breast cancer, although researchers did adjust their findings for a range of other risk factors.
As the authors point out, it is crucial that young women are informed about the health risks of drinking alcohol regularly.
Aside from any increase in breast cancer risk, regularly drinking more than the recommended limit can lead to liver disease, reduced fertility, high blood pressure, increased risk of various other cancers, heart attack, stroke and mental health problems.
Read more about the risks of drinking too much.