Why do smart people live longer?

Indeed, the impact of intelligence on mortality rivals well-known risk factors for illness and death, such as high blood pressure, being overweight, high blood glucose, and high cholesterol. Its effect is almost as important as that of smoking.

Differences in human intelligence have environmental and genetic causes. An intelligence test score in early life is partly a record of what the environment has wrought on the brain and the rest of the body up to that time. Babies who have lower birth weights, for example, are more prone to chronic illnesses later in life. They also have, on average, slightly lower intelligence. But tests of whether birth weight might explain some of the link between intelligence and mortality have found no connection.