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Marin County’s high breast cancer rate may be linked to genetics

Posted on: August 9, 2012   by  Vitamin D Council


Marin County in the Bay area has an unusually high incidence of breast cancer, a mystery researchers have long been trying to decipher.

The number of new breast cancer cases in Marin County is 40% higher than the national average.

Researchers working at the University of California San Francisco provide new insight into this paradox. A study published online this week in the Journal of the American College of Surgeons suggests genetic variations in the vitamin D receptor – a protein molecule which signals the cell to activate vitamin D – may be to blame.

Dr Kathie Dalessandri, MD, and colleagues performed DNA genotyping on 164 Caucasian women diagnosed with breast cancer from 1997 to 1999 living in Marin County. They also tested 174 controls matched for ethnicity and age. The authors determined individual lifetime risk using the polyfactorial risk model. Based on that analysis, women at increased risk were compared with the overall genotypes.

The researchers found that the vitamin D receptor variation was more prevalent in women with an elevated risk of developing breast cancer. Sixty-four percent of women who had an elevated risk of breast cancer had the vitamin D receptor variation, compared with 34% of women in the overall study population (p = 0.0003).

The authors conclude,

“The high frequency of the VDR Apa1 A2/A2 homozygous polymorphism in women designated as elevated risk for breast cancer… might be related to the high incidence rates of breast cancer in Marin County, California. Vitamin D supplementation could modify risk of breast cancer in this population. “

Researchers are in the process of conducting a follow up study with a larger sample size to gain further insight into this new finding.


Dalessandri KM, et al. Vitamin D receptor polymorphisms and breast cancer risk in a high-incidence population: A pilot study. Journal of American College of Surgeons. Aug 2012.

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