A happy camper is a healthy camper, say British researchers who have unearthed evidence of a biological connection between a positive sense of well-being and reduced risk for disease among middle-aged men and women.

In this week's issue of the Proceedings of the National Academy of Sciences, the authors report that simply being happy -- at work and at play -- is directly related with specific bodily functions that protect against cardiovascular disease, diabetes, autoimmune deficiencies and stress-related illnesses.

"There's a direct link between how we're feeling and the biological processes which relate to illness and illness risk," said study author Dr. Andrew Steptoe, the British Heart Foundation professor of psychology at University College London. "Biology is going to be on the side of those people who are going to be in a more positive state of mind, and it may well stand these people in good stead for their future health."

Steptoe and his colleagues administered laboratory stress tests and standardized mental health questionnaires to more than 200 white men and women in the London area, aged 45 to 59.

All the participants were employed civil servants, with income levels ranging from high to low. Medical exams had determined that all were in relatively good physical health, with no prior history of heart disease or high blood pressure.

Blood samples were taken before and after the stress tests. The researchers then followed each participant over the course of a single routine workday, using portable monitors to automatically assess their blood pressure and heart rate every 20 minutes from the start of work until bedtime.

All the men and women kept a diary of their location and activities throughout the monitoring. They also rated how happy they felt -- on a scale of one to five -- at the time of each assessment. Rankings of momentary feelings of stress, control, and/or fatigue were also noted.

Shifting levels of the stress hormone cortisol were additionally measured with saliva samples that the participants were asked to collect every two hours during the same work day, and on a separate leisure day.

The researchers reported that age, marital status, gender and income appeared to have no impact on how happy the participants said they felt while at work.

Steptoe and his team also observed that those men and women who demonstrated the lowest levels of psychological distress on the earlier mental health screenings appeared to be generally happier people.

And those men and women who were happiest at work seemed to be happiest at play, they said -- although, for all participants, happiness was in more abundance during days off at home than during days "on" at the office.

Among the biological markers explored, not all appeared to influence happiness. Blood pressure was not associated with the participants' self-assessed happiness, while heart rate appeared to be a factor only among men -- being highest among the least happy men.

However, cortisol readings did appear to firmly back the notion of a biological connection between stress and happiness. The researchers found the happiest men and women had the lowest levels of cortisol. Cortisol levels were, on average, more than 32 percent higher among the least happy individuals.

The researchers noted the danger that high stress hormone levels can pose over time, highlighting the association between elevated cortisol and a higher risk for developing high blood pressure, diabetes, abdominal obesity and a decreased resistance to infection.

On another biological front, the authors reported that blood tests revealed up to 12 times higher levels of a liver-produced protein known as plasma fibrinogen among the least happy men and women.

Fibrinogen works to stop bleeding by helping clots to form, but elevated levels of the protein have been associated with a higher risk for cardiovascular disease.

The researchers concluded that a having a strong sense of well-being and happiness may help boost biological systems, ultimately helping to lower the risk for developing a range of illnesses down the road. And they emphasized that this happiness-healthiness pathway appears to be a direct mind-body link that is independent of lifestyle choices, such as exercise, smoking and drinking.

"There's no doubt that people should do the healthy lifestyle things -- being physically active, and more prudent in their diets, and not smoking -- irrespective of this biological link," Steptoe advised. "But we need to think about things that will lead to more positive states as well. Doing things that you want to do, and getting gratification from those things."

But Steptoe cautioned that the road to becoming a happier -- and thereby healthier -- person can be tricky to navigate.

"I can't really prescribe how people should make themselves happier, because philosophers have failed at that for centuries," he said. "But most of our sense of happiness seems to relate to having good relationships with family and friends, and that's not something that can be maintained without some investment of effort, and keeping an appropriate balance. That balance, of course, is going to be different for different people."

Dr. Albert Ray is regional coordinator for health promotion and preventive care for Kaiser Permanente Southern California in San Diego. He said, "I try to give people concrete things to do to help de-stress. Get a dog, get a cat, go out, play sports, go to their religious institution, do yoga, get married, have a relationship, go on a vacation, do things that can relax a person."

Ray wholeheartedly applauded the researchers' ability to isolate the biological evidence for the effect happiness has on our bodies -- something he said he's observed anecdotally for years.

"There's no question that people with a positive attitude have lower blood pressure, suffer less illness, usually have lower cholesterol and better resistance to most infections," he said. "And when they do get sick, usually a positive attitude can result in shorter illness."

"And I think every doctor tries to tell their patient to get out and smell the flowers, go for a walk, read a book, and try and look on the bright side rather than have a negative outlook," Ray added. "It just seems sensible to reason. Even without being a doctor."

More information

For more on happiness and well-being, check with the American Psychological Association.