In a joint study on personality, conducted by Harvard University and Boston University, 1,306 men were tracked over a ten-year period. After the ten-year period, the 1,306 men were put through a battery of tests to determine their health. The men designated as pessimistic were twice as likely to have heart disease. The men designated as optimistic were much healthier and showed few signs of heart disease.
A similar four-year study conducted by researchers in Finland showed similar results. Pessimistic men were three times more likely to develop hypertension and high blood pressure than their optimistic counterparts.
A University of Illinois study found that optimists had significantly lower blood sugar levels and a lower body mass index than pessimists.
There are many other studies I could cite. They all seem to point to the same thing: Optimists are healthier and live longer than pessimists. Even diseases ravage pessimists more than optimists because pessimists have a weaker immune system according to various studies.
Optimism, like habits, is contagious. It affects those within your social network. Optimism not only improves your health and increases your longevity, it also improves the heath and longevity of your family, friends and coworkers. So, the lesson here is to hang around optimistic people because pessimism can kill you. Pessimists are toxic in many ways that go beyond just derailing your from achieving success in life. Avoid pessimists like the plague.