Whole and refined grain intake and risk of incident postmenopausal breast cancer (United States).
OBJECTIVE
To assess the relation between whole and refined grain intake and risk of incident postmenopausal breast cancer. Findings from case-control studies of whole and refined grain intake and risk of postmenopausal breast cancer have been inconclusive.


METHODS
The Iowa Women's Health Study is a prospective cohort study of women initially 55-69 years old that relates diet and other lifestyle factors to cancer risk. After exclusions a total of 29,119 menopausal women who answered a 1986 baseline and a 1989 follow-up questionnaire were followed for 9 years for incident breast cancer.


RESULTS
Compared to women who at baseline rarely ate whole grain foods, women who habitually ate whole grain had a healthier lifestyle, including a higher likelihood of prior screening mammography. The multivariate-adjusted risk of incident breast cancer was 20% higher in women in the highest quintile of whole grain intake, compared to women in the lowest quintile of whole grain intake (95% confidence interval 0.95-1.5; p-value for trend = 0.03). No increase in breast cancer risk was found in women who had not undergone screening mammography before 1989; the apparent increase in risk was therefore likely due to increased use of screening mammography. Refined grain intake was not associated with breast cancer risk.


CONCLUSIONS
Consistent with inverse but not statistically significant associations between whole grain intake and breast cancer in case-control studies, both whole and refined grain intakes are unrelated to risk of postmenopausal breast cancer in these Iowa women.
Nicodemus
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Division of Epidemiology, School of Public Health, University of Minnesota, Minneapolis 55454-1015, USA.
Jacobs
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DR
Folsom
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D000368:Aged; D001943:Breast Neoplasms / Q000175:diagnosis / Q000453:epidemiology*; D004032:Diet; D002523:Edible Grain; D005260:Female; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D017698:Postmenopause / Q000502:physiology*; D011446:Prospective Studies; D012307:Risk Factors; D014481:United States / Q000453:epidemiology; D016387:Women's Health