Women who live in Northern cities where towering buildings block what feeble winter sun there is may have a higher risk of breast cancer than women in sunny regions, a new study suggests.
Researchers theorize that the women in these darker cities are not exposed to enough sunlight to allow their bodies to synthesize vitamin D.
The study, by two University of California researchers, compared breast cancer death rates with the amount of solar radiation calculated to be striking the ground at 87 regions around the United States.
Plotting the two sets of statistics on a graph, Dr. Frank C. Garland, his brother, Dr. Cedric F. Garland, and colleagues at the University of California in San Diego discovered that as a general rule the cities with the lowest light levels also had the highest breast cancer death rates.
The results of the study appear in the journal Preventive Medicine.