Japan has 18% smokers vs. 12.5% in the US. They have a five year longer life expectancy but they also have universal healthcare, so it's not really a fair comparison. Plus, Japan has good air quality and robust elder care.

On top of that, they may have chemical factors (such as no lithium mines) that differentiate them from other developed countries.

Smoking decreases appetite. A lot of people who quit smoking gain significant weight.