During an average of 7 years of follow-up, we identified 5,461 breast cancer cases (3,531 ductal, 550 lobular, 424 ductal-lobular, and 956 other tumors). A total of 3,341 breast cancers were identified from state cancer registries that reported hormone receptor status, with 1,641 ER+/PR+, 336 ER+/PR−, 48 ER−/PR+, and 366 ER−/PR− tumors and 950 tumors with either unknown estrogen receptor or progesterone receptor status. The distribution of the various subtypes of breast cancer was consistent with those reported in other studies (
1,
2). We do not present results for ER−/PR+ tumors because of the small number of cases.
Thirty percent of women did not consume alcohol, while 54% and 16% of women consumed ≤10 g and >10 g of alcohol per day, respectively. Compared with nondrinkers, women who consumed alcohol tended to be physically active, to smoke more, to be nulliparous, to use MHT, and to have lower intakes of total folate and total fat (). The characteristics of women in states for which hormone receptor status was available did not differ from those of women in states where hormone receptor status was not available (data not shown).
| Table 1.Baseline Characteristics by Categories of Alcohol Intake Among Postmenopausal Women in the NIH-AARP Diet and Health Study, 1995–2003 (n = 184,418) |
Alcohol intake was significantly positively associated with total breast cancer (). The significantly increased risk of total breast cancer was found in both moderate and heavy drinkers: Compared with nondrinkers, women who consumed 10–<20, 20–35, and >35 g/day of alcohol showed risk increases of 13%, 23%, and 35%, respectively (
Ptrend
<

0.001). The association between alcohol intake and total breast cancer did not differ by ascertainment of hormone receptor status. The multivariate relative risk for >35 g versus 0 g/day of alcohol was 1.40 (95% CI: 1.16, 1.69) among women in states with available hormone receptor status information and 1.30 (95% CI: 1.03, 1.63) among women in those states without hormone receptor status data. This positive association of alcohol with breast cancer was observed for all different histologic types of breast cancer. For >35 g versus 0 g/day of alcohol, the multivariate relative risks were 1.46 (95% CI: 1.22, 1.75;
Ptrend
<

0.001) and 1.52 (95% CI: 0.95, 2.44;
Ptrend
=

0.04) for ductal and lobular tumors, respectively. The multivariate relative risks for an increment of 10 g/day of alcohol were 1.04 (95% CI: 1.02, 1.05) for total breast cancers, 1.04 (95% CI: 1.02, 1.06) for ductal tumors, 1.03 (95% CI: 0.98, 1.08) for lobular tumors, and 1.03 (95% CI: 0.97, 1.09) for ductal-lobular tumors. For an increment of 1 drink/day, the multivariate relative risks were 1.05 (95% CI: 1.03, 1.07) for total breast cancer, 1.05 (95% CI: 1.03, 1.08) for ductal tumors, 1.04 (95% CI: 0.98, 1.11) for lobular tumors, and 1.04 (95% CI: 0.96, 1.12) for ductal-lobular tumors. When we examined the associations after excluding breast cancer cases diagnosed within the first 2 years of follow-up, the results did not change.
| Table 2.Relative Risks and 95% Confidence Intervals of Total Breast Cancer and Breast Cancer by Histologic Type for Categories of Alcohol Intake, NIH-AARP Diet and Health Study, 1995–2003 |
The positive association between alcohol and breast cancer risk was observed for all types of alcoholic beverages. In a comparison of ≥3 and 0 drinks/day, the multivariate relative risks were 1.36 (95% CI: 1.16, 1.59;
Ptrend
<

0.001; median intake = 4.4 drinks/day) for total alcoholic beverages, 1.73 (95% CI: 1.22, 2.47;
Ptrend
<

0.001; median intake

=

7.2 drinks/day) for beer, 1.39 (95% CI: 0.86, 2.24;
Ptrend
=

0.004; median intake

=

5.6 drinks/day) for wine, and 1.24 (95% CI: 1.03, 1.49;
Ptrend
=

0.001; median intake

=

5.2 drinks/day) for liquor, with mutual adjustment for each alcoholic beverage type.
When we subdivided breast cancers according to their hormone receptor status, alcohol intake was significantly positively associated with ER+ and PR+ tumors, but not with ER− and PR− tumors. In a comparison of women who consumed >35 g/day of alcohol with nondrinkers, the multivariate relative risks were 1.50 (95% CI: 1.19, 1.90;
Ptrend
<

0.01; 2,074 cases) for ER+, 1.46 (95% CI: 1.12, 1.90;
Ptrend
=

0.003; 1,700 cases) for PR+, 0.81 (95% CI: 0.42, 1.58;
Ptrend
=

0.90; 418 cases) for ER−, and 1.17 (95% CI: 0.76, 1.81;
Ptrend
=

0.25; 704 cases) for PR− tumors. When hormone receptor status was further defined by both estrogen receptor and progesterone receptor, a statistically significant positive association with alcohol was found for ER+/PR+ tumors but not for ER−/PR− tumors (). However, the association between alcohol intake and breast cancer did not differ statistically by hormone receptor status. The multivariate relative risks for an increment of 10 g/day of alcohol were 1.04 (95% CI: 1.01, 1.08) for ER+/PR+ tumors and 1.00 (95% CI: 0.93, 1.08) for ER−/PR− tumors. For an increment of 1 drink/day, the multivariate relative risks were 1.05 (95% CI: 1.01, 1.09) and 1.02 (95% CI: 0.93, 1.11) for ER+/PR+ and ER−/PR− tumors, respectively.
| Table 3.Relative Risks and 95% Confidence Intervals of Breast Cancer Risk by Hormone Receptor Status for Categories of Alcohol Intake, NIH-AARP Diet and Health Study, 1995–2003 |
We examined alcohol intake in relation to breast cancer defined by both histologic types and estrogen receptor status. The multivariate relative risks for an increment of 10 g/day of alcohol were 1.05 (95% CI: 1.02, 1.08) for ER+ ductal tumors, 1.00 (95% CI: 0.91, 1.09) for ER+ lobular tumors, 0.98 (95% CI: 0.90, 1.07) for ER− ductal tumors, and 1.03 (95% CI: 0.82, 1.30) for ER− lobular tumors.
The association between alcohol and total breast cancer was not modified by total folate intake, body mass index, or MHT use (). Although the interactions with MHT use were not statistically significant, the association between alcohol and total breast cancer appeared stronger in long-term MHT users. When we examined the association by the combination of MHT status and duration of use, we found that the association was stronger in long-term current users. In a comparison of >35 g and 0 g/day of alcohol, the multivariate relative risks were 1.66 (95% CI: 1.25, 2.22) in current MHT users for ≥10 years, 1.18 (95% CI: 0.88, 1.58) in current MHT users for <10 years, and 1.11 (95% CI: 0.64, 1.94) in former MHT users for <10 years (data not shown for former MHT users for ≥10 years because of the small number of cases). We also found no effect modification of the alcohol and breast cancer relation by family history of breast cancer, history of breast biopsy, or smoking status (data not shown).
| Table 4.Multivariate Relative Risksa and 95% Confidence Intervals of Breast Cancer for Categories of Alcohol Intake, Stratified by Total Folate Intake, Body Mass Index, and Menopausal Hormone Therapy, NIH-AARP Diet and Health Study, 1995–2003 |