Japan was not always a longevity champion. In 1970 its age-adjusted mortality rates were average for the OECD . Although its levels of cancer and heart disease were relatively low, it also had the OECD ’s highest frequency of cerebrovascular deaths, caused by blood failing to reach the brain.

Committed couples do have more sex than everyone else. But Americans who are not having that much physical intimacy are just as happy as their more active counterparts.

Sexual frequency declines 3.2 percent a year after the age of 25. But the good news is that what married couples lack in ...