4009

Potential reduction in breast cancer risk associated with Vitamin D

Tuesday, Apr 04, 2006, 11:25 AM -11:40 AM

Room 206, Washington Convention Center

Julia A. Knight, Maia R. Lesosky, Heidi Barnett, Janet M. Raboud, Reinhold Vieth. Mount Sinai Hospital, Toronto, ON, Canada

Background: Experimental studies provide evidence that vitamin D could potentially be used to prevent and/or treat breast cancer. The epidemiologic evidence relating vitamin D to breast cancer risk is, however, extremely limited. Vitamin D is primarily obtained through sun exposure, but dietary sources also can contribute to the total vitamin D exposure. We are conducting a population-based case-control study in Ontario, Canada to gain additional evidence on the relationship between vitamin-D related exposures and the risk of breast cancer. Methods: Incident cases (a 35% random sample) are being identified through the Ontario Cancer Registry and population controls, frequency-matched by five-year age group, are being recruited through randomly selected residential telephone numbers. Cases are contacted once permission is received from a physician. Information is collected through a telephone interview. Results: We have received physician consent to contact approximately 84% of the cases and 72% of these cases have completed the interview. Approximately 70% of eligible control women identified on the telephone have agreed to participate and approximately 83% of these have completed the interview. We have conducted a preliminary analysis on the portion of the data that was most complete: 576 cases diagnosed from July 1, 2003 to June 30, 2004 and aged 20 to 59 and 813 controls aged 20 to 59. Unconditional logistic regression was used to obtain odds ratios (OR) and 95% confidence intervals (CI) and each vitamin-D related variable was adjusted for age, ethnicity, education, having a first degree relative with breast cancer, ever breastfeeding for at least one month, age at menarche, and age at first birth. There was evidence for a reduction in breast cancer risk associated with the following sun exposure variables: ever working in an outdoor job (OR=0.60, 95% CI 0.48-0.75), number of different outdoor activities at ages 10 to 19 (OR=0.55, 95% CI 0.39-0.77 for >6 vs. <4) and at ages 20 to 29 (OR=0.72, 95% CI 0.52-1.00 for >5 vs. <3) as well as the highest vs. lowest quartile of number of outdoor activity episodes at ages 10 to 19 (OR=0.68, 95% CI 0.49-0.93) and at ages 20 to 29 (OR=0.66, 95% CI 0.48-0.91). Note that “outdoor activities” includes those that do not involve physical activity. Taking cod liver oil for 10 years or more was also associated with reduced risk (OR=0.64, 95% CI 0.40-1.00) as was consumption of >9 glasses of milk per week compared to <5 at ages 20 to 29 (OR=0.75, 95% CI 0.58-0.99). Conclusions: This preliminary analysis provides support for the hypothesis that vitamin D may reduce the risk of breast cancer and earlier exposures may be more important than recent exposure. Additional analyses will separate those activities involving exercise from those that do not.