There are many sources that indicate that people are healthier and live longer than people 100 years ago. I have also seen studies that show IQs are higher by something like a standard deviation than those of our recent ancestors.
The latter is called the Flynn Effect and I think a major cause is supposed to be improved nutrition which sounds plausible to me. Air pollution being significantly less (elimination of leaded gasoline) has also been mentioned. But what I wonder is, how reasonable is it to attribute the differences to the prevalence of fireplaces and gas flames being used by people prior to modern heating and lighting? Is it possible that literally millions of people had chronic, low-level carbon monoxide poisoning, not to mention the effects of particulate matter that they were inhaling?
EDIT: And in the present, in the developing world, people might also be affected by the same thing. A reason to try to get the benefits of reliable electricity to more of our fellow humans.