The qualities of being a closed population, as well as good genealogical records, make the Amish an attractive group for genetic and health-related studies.
In a recently-reported Ohio State study, researchers theorized about higher rates of cancer, but found the opposite. They discovered that Amish in Holmes County, Ohio exhibit cancer rates only 56% of the national average.
The researchers explain that low cancer rates are likely linked to both genetics and behavioral differences.
Lower levels of tobacco and alcohol use, and less sexual promiscuity among Amish mean that related cancers are less likely to appear.
They also note that Amish exhibit low levels of skin cancer, though one would expect them to spend more time in the sun than the average American (though this is apparently linked to lifestyle as well–as Amish would be more likely to work using hats and with skin covered by long-sleeved clothing).
The closed Amish gene pool leads to beneficial and harmful results. Last year stories showed Amish exhibit lower rates of obesity, while certain rare genetic diseases appear among Amish much more frequently than in the general population.
This is one example where it looks like both lifestyle and genes lead to an overall healthier Amish population, at least regarding cancer.