BBD information was obtained from 6899 females, who provided 67 biopsy-confirmed BBD cases and 6752 non-cases for analyses. Most GUTS females are white/non-Hispanic (95%), as are most of these BBD cases. One case reported “other” race, one case reported being both white and American Indian or Alaskan native, and one did not complete the race question.
Baseline (1996) data of females who returned the 2005 and/or 2007 survey(s) (77% of the original cohort) are compared with those who returned neither survey and thus had no BBD information to contribute to these analyses. At baseline, the included girls tended to be slightly younger (by 0.108 yr, p<.01) than those not included here; otherwise, they were similar at baseline, in body weight (age-adjusted baseline BMI difference of 0.08 kg/m2, p=.32) and total calories (19 kcal/day difference, p=.24). Thus, we may be missing some older participants who were diagnosed with BBD during follow-up.
BBD cases and non-cases had similar mean age at menarche (12.8yr vs 12.6yr). Cases and non-cases became regular drinkers (drank at least monthly) at similar ages (both means 19.0yr) though more non-cases never became regular drinkers (20% vs 12%) through year 2008. More cases had mothers with a history of breast cancer (6% vs 3.2%) or BBD (26.9% vs 18.5%) than non-cases. Cases tended to be thinner at time of disease reporting (mean BMI= 22.9 kg/m2 for cases compared to 23.7 for non-cases).
shows means and percents, by BBD case status, of alcohol factors from the 2003 survey. Females were aged 16 through 23 years when they provided these alcohol data; the BBD cases were about 8 months older in 2003, drank alcohol more frequently, consumed more at each drinking occasion, and average daily consumption was more than twice as high. Cases also reported more episodes of binge drinking.
Alcoholic beverage factors, reported in 2003, by benign breast disease (BBD) case status, reported from 2005 through 2008a
In BMI- and age-adjusted analyses, typical alcohol intake (OR=1.50 per drink/day, 95%CI: 1.19, 1.90) from the 2003 survey was associated with higher BBD risk (). Stratifying by BMI quartiles showed the risk persisted within BMI subgroups (OR=1.61 per drink/day for the most lean, and OR=1.51 for the heaviest women; not shown). BMI- and age-adjusted analyses of drinking frequency also found an association (OR=5.50 for those drinking 6 or 7 days/week relative to those drinking less than once per week; 95%CI: 1.23, 24.53) (). The two variables “drinking frequency” and “drinks per occasion” are highly correlated; when included together in a model, frequency of drinking was more important (, bottom).
Alcoholic beverage variables (2003) and risk of benign breast disease (diagnoses reported from 2005 through 2008)a
To show that these findings were not confounded by a series of other factors, we re-fit the “drinks per day” model adjusting for them individually. Including age at menarche (not itself significant) in the model did not modify the estimate of risk for alcohol, nor did adjusting for maternal breast cancer and maternal biopsy-confirmed BBD, neither of which were significant. Adjusting for age at onset of regular drinking (among those who became regular drinkers; also not significant) similarly did not substantially affect the estimated risk per drink/day in 2003.
Mean alcohol intakes generally doubled from one year of age to the next until age 18yr, and therefore intakes at ages younger than 18 may not correspond to the exposure levels relevant to BBD risk (particularly for girls who did not drink at all before college). Analyses stratified by age () found elevated BBD risk with higher alcohol consumption at ages 19 (OR=1.76 per drink/day, 95%CI: 1.19–2.60) and 21+ (OR=1.51 per drink/day; 95%CI 1.02–2.26). Intakes at other ages suggested similarly elevated risks, though not statistically significant (). Pooling together females aged 18yr+ at time of 2003 alcohol report, the BBD risk was OR=1.51 per drink/day (95%CI: 1.19, 1.92).
Adolescent alcohol intake and risk of benign breast disease in young women, by age when alcohol intake was reporteda
To see if conclusions persisted, models were re-estimated using alcohol data obtained from earlier survey years, 2000 and 2001. Of the females who provided BBD information, 54 cases and 5623 non-cases returned surveys in year 2000, and 53 cases and 5542 non-cases in year 2001. From year 2000 alcohol intakes, the risk of BBD was OR=1.56 per drink/day (95%CI: 0.87, 2.77), and from year 2001 intakes OR=1.46 per drink/day (95%CI 0.96, 2.19). Restricting estimation of these models to females who were 18yr and older when reporting alcohol, the BBD risk was OR=2.24 (95%CI: 1.20, 4.18) per drink/day reported in 2000, and OR=1.51 per drink/day (95%CI: 0.99, 2.31) reported in 2001. The 18+ year-olds in year 2000 have more years of alcohol exposure before BBD reporting began in 2005, than the larger number of 18+ year-olds in 2003, which may explain their different estimates. The 2001 survey asks separately about beer, wine and liquor, and thus the 2001 summed intake may differ in accuracy from the other surveys. The dissimilarities among the alcoholic beverage question formats on the surveys (2000, 2001, 2003) hinder the analysis of cumulative mean exposures; however, we cautiously report that analyzing cumulative average consumption (2000 through 2003) also indicated increased risk (OR=1.64 per drink/day, 95%CI: 1.11, 2.42) for BBD.
Sensitivity analyses were conducted to see how results differed under alternative case definitions. Using a weaker definition, in which all reports of BBD (including those not confirmed by biopsy) are considered cases (n=147), the risk associated with 2003 alcohol was OR=1.26/drink per day (95%CI: 1.04, 1.53). A stronger case definition that required two reports of biopsy-confirmed BBD (in both 2005 and 2007; n=27 females) estimated the 2003 alcohol risk as OR=1.60 per drink/day (95%CI: 1.16, 2.19). Thus, 2003 alcohol consumption was significantly associated with increased risk of BBD, no matter how we defined BBD cases.