However, people don't live all those years in perfect health. At some point in your life, you will have some level of disability. These years with disability are weighted according to their level of severity to estimate the total equivalent lost years of good health. You subtract this from total life expectancy, and what remains is the expected number of years of healthy life. This is the first time that anyone has measured every country's healthy life expectancy using the DALE system.
Several factors go into making Japan number one in the rankings.
One is the low rate of heart disease, associated with the traditional low fat diet. The national diet is changing, with high fat foods such as red meat becoming common. The effect of tobacco has also been mild until recently, with low lung cancer rates. In Australia, smoking rates have dropped sharply from their earlier peaks, leading to lower lung cancer and heart problem rates. France registered high because of the health of its women, which pulled up the overall average.