What's the secret to living to 100? Some say it's ensuring plenty of exercise; others point to the benefits of a mild climate. There are even some who suggest that a healthy sex life has plenty do with it.

The number of people who live to 100 may be relatively small, but it's becoming more common -- particularly in countries like Japan, which has the highest proportion of centenarians in the world.

Data from Japan's Ministry of Health estimate that there were 67,824 Japanese people 100 or older as of 2017. In 1965, when the country began recording statistics on its senior citizens, there were just 153 centenarians.

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