researchers writing in The American Journal of Cardiology have found better levels of "good cholesterol" and other markers of heart health in the blood of middle-aged study subjects with a sunny outlook on life.
At least some of the connection between optimism and blood lipids in the new study appeared to result from the optimists' tendency to have a healthy body weight and a "prudent" diet, according to researchers.
"It is one additional piece of evidence suggesting that our psychological health and physical health are intertwined, and that viewing the world optimistically may have some tangible benefits for our health," said lead author Julia Boehm, a research fellow at the Harvard School of Public Health.
Previous research by Boehm and her colleagues had shown a link between optimism and lowered heart attack risk, so they decided to look at whether there was an independent connection between optimistic or pessimistic outlooks and cholesterol, which is known to play a role in heart attack risk.
The group analysed data from the Midlife in the United States study, which included phone interviews and lab tests for 990 people aged 40 to 70.
Based on the interviews, participants' levels of optimism were rated on a scale from six to 30 depending on their agreement or disagreement with statements like "in uncertain times I usually expect the best".
People with higher optimism scores also had more high-density lipoprotein (HDL), the desirable form of cholesterol that is believed to protect against heart disease. They also had lower levels of triglycerides, the fatty molecules involved in hardening of the arteries.
There was no connection between optimism and total cholesterol levels, or to low-density lipoproteins (LDL), the "bad" cholesterol. For every increase of five points on the optimism scale, however, HDL in the blood increased by 1 milligram per decilitre.
That same HDL increase would translated to a 3pc reduction in the risk for heart disease, experts said. For comparison, regular exercise can decrease heart disease risk by 6pc.