Dairy, calcium, and vitamin D intake and postmenopausal breast cancer risk in the Cancer Prevention Study II Nutrition Cohort.
BACKGROUND
Calcium, vitamin D, and dairy products are highly correlated factors, each with potential roles in breast carcinogenesis. Few prospective studies have examined these relationships in postmenopausal women.


METHODS
Participants in the Cancer Prevention Study II Nutrition Cohort completed a detailed questionnaire on diet, vitamin and mineral supplement use, medical history, and lifestyle in 1992 to 1993. After exclusion of women with a history of cancer and incomplete dietary data, 68,567 postmenopausal women remained for analysis. During follow-up through August 31, 2001, we identified 2,855 incident cases of breast cancer. Multivariate-adjusted rate ratios (RR) were calculated using Cox proportional hazards models.


RESULTS
Women with the highest intake of dietary calcium (>1,250 mg/d) were at a lower risk of breast cancer than those reporting < or =500 mg/d [RR, 0.80; 95% confidence interval (95% CI), 0.67-0.95; P(trend) = 0.02]; however, neither use of supplemental calcium nor vitamin D intake was associated with risk. Consumption starting at two or more servings of dairy products per day was likewise inversely associated with risk (RR, 0.81; 95% CI, 0.69-0.95; P(trend) = 0.002, compared with <0.5 servings/d). The associations were slightly stronger in women with estrogen receptor-positive tumors comparing highest to lowest intake: dietary calcium (RR, 0.67; 95% CI, 0.51-0.88; P(trend) = 0.004); dairy products (RR, 0.73; 95% CI, 0.57-0.93; P(trend) = 0.0003), and dietary vitamin D (RR, 0.74; 95% CI, 0.59-0.93; P(trend) = 0.006).


CONCLUSIONS
Our results support the hypothesis that dietary calcium and/or some other components in dairy products may modestly reduce risk of postmenopausal breast cancer. The stronger inverse associations among estrogen receptor-positive tumors deserve further study.
McCullough
Marjorie L
ML
Epidemiology and Surveillance Research, American Cancer Society, 1599 Clifton Road Northeast, Atlanta, GA 30329-4251, USA. marji.mccullough@cancer.org
Rodriguez
Carmen
C
Diver
W Ryan
WR
Feigelson
Heather Spencer
HS
Stevens
Victoria L
VL
Thun
Michael J
MJ
Calle
Eugenia E
EE
D001943:Breast Neoplasms / Q000453:epidemiology* / Q000209:etiology; D002136:Calcium, Dietary / Q000008:administration & dosage*; D003611:Dairy Products; D005260:Female; D006801:Humans; D015994:Incidence; D008019:Life Style; D008875:Middle Aged; D017698:Postmenopause; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D011795:Surveys and Questionnaires; D014481:United States / Q000453:epidemiology; D014807:Vitamin D / Q000008:administration & dosage*
D002136:Calcium, Dietary; D014807:Vitamin D