Vitamin D and reduced risk of breast cancer: a population-based case-control study.
BACKGROUND
Vitamin D, antiproliferative and proapoptotic in breast cancer cell lines, can reduce the development of mammary tumors in carcinogen-exposed rats. Current evidence in humans is limited with some suggestion that vitamin D-related factors may reduce the risk of breast cancer. We conducted a population-based case-control study to assess the evidence for a relationship between sources of vitamin D and breast cancer risk.


METHODS
Women with newly diagnosed invasive breast cancer were identified from the Ontario Cancer Registry. Women without breast cancer were identified through randomly selected residential telephone numbers. Telephone interviews were completed for 972 cases and 1,135 controls. Odds ratios (OR) and 95% confidence intervals (CI) for vitamin D-related variables were estimated using unconditional logistic regression with adjustment for potential confounders.


RESULTS
Reduced breast cancer risks were associated with increasing sun exposure from ages 10 to 19 (e.g., OR, 0.65; 95% CI, 0.50-0.85 for the highest quartile of outdoor activities versus the lowest; P for trend = 0.0006). Reduced risk was also associated with cod liver oil use (OR, 0.76; 95% CI, 0.62-0.92) and increasing milk consumption (OR, 0.62 95% CI 0.45-0.86 for >or=10 glasses per week versus none; P for trend = 0.0004). There was weaker evidence for associations from ages 20 to 29 and no evidence for ages 45 to 54.


CONCLUSIONS
We found strong evidence to support the hypothesis that vitamin D could help prevent breast cancer. However, our results suggest that exposure earlier in life, particularly during breast development, maybe most relevant. These results should be confirmed.
Knight
Julia A
JA
Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 60 Murray Street, Box 18, Toronto, Ontario, Canada M5T 3L9. knight@mshri.on.ca
Lesosky
Maia
M
Barnett
Heidi
H
Raboud
Janet M
JM
Vieth
Reinhold
R
D000328:Adult; D000368:Aged; D000818:Animals; D001943:Breast Neoplasms / Q000453:epidemiology* / Q000517:prevention & control*; D016022:Case-Control Studies; D003060:Cod Liver Oil / Q000008:administration & dosage; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D016015:Logistic Models; D008875:Middle Aged; D008892:Milk; D009864:Ontario / Q000453:epidemiology; D012042:Registries; D012307:Risk Factors; D013472:Sunlight; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000494:pharmacology*
D014807:Vitamin D; D003060:Cod Liver Oil