Japan’s population of centenarians is the largest in the world. Most of the 28,000 Japanese who have made it beyond 100 are women and the highest concentration of the very elderly is in the southern part of the archipelago. The area around Hiroshima and the island of Okinawa are especially rich in former “world’s oldest” title holders.This may well be an example of a phenomenon known as hormesis. The common theory about exposure to chemicals or radiation, any exposure is bad and more is cumulatively worse, also known as LNT (linear no threshold). The theory of hormesis posits that small doses have a health benefit, possibly through stimulation of the immune system, but beyond some optimum level the positive effects diminish and turn progressively more negative. I don't know that this idea has been proven but there is considerable evidence in support. The dosage makes the poison. This has very different implications than LNT when formulating health guidelines are environmental regulations. Nobody told you? Now you've read the idea. A website is here and a book is here. After reading the book I am much less concerned about the difficulty of dealing with spent fuel from nuclear reactors.
Someday low dose exposure to various substances may be part of recommended health routines!