http://www.washingtonpost.com/wp-dyn/content/article/2008/02/19/AR2008021902398.html

Women who sleep in dark neighborhoods are less likely to get breast cancer. I would attribute this to only a few things. Power lines produce beta radiation and high power electromagnetic fields. These factors can influence biology. Otherwise, it would be from increased generic pollution from population density. But if this study is evenly weighted the electrical fields, which have been shown to influence health in other ways, are contributors.