After I quit smoking in the summer of 2015 I got a bunch of health checks to make sure I was ok. One of these was a chest xray, which indicated lung cancer. (I had no symptoms not even a cough.)

After a long wait (socialized medicine) in Canada I finally had surgery and then chemo. I got lung cancer because I smoked for 35 years not because i have bipolar or schizoaffective disorder.

A lot of people with bipolar disorder smoke, drink to excess and/or use illegal drugs in harmful ways. Add that to the adverse effects of long term medications, poor diet, inactivity and suicide so it is not that surprising that you can end up with a difference
in life expectancy.

There may be an increased risk of early death just from having bipolar but I don't see how it could be disentangled from the adjustable risks including smoking.

Editted to add: people with bipolar are also more likely to end up homeless or in prison, both of which decrease life expectancy.