Researchers analyzed telephone interviews and laboratory results from 990 people between the ages of 40 and 70 and found that optimists were less likely to have higher levels of bad cholesterol (i.e. LDL) and higher levels of good cholesterol (i.e. HDL), which protected the heart and helped counteract bad cholesterol. 
During the experiment each five-point increase in the optimism score was associated with a 1-milligram increase in HDL per 100 milliliters of blood, which translates to a 3 percent lower risk of heart disease.
 the study believes that mental health and physical health are closely related to another evidence that optimistic temperament may have some real benefits for human health.