Many studies support the belief that having an upbeat and positive attitude will translate into living a longer, healthier life, and conversely, that a pessimistic outlook promotes ill health and can shave years off your life. 

For example, in one study, the tendency to always expect the worst was linked to a 25 percent higher risk of dying before the age of 65.

Perhaps one of the most well-known forerunners of "the science of happiness" was Norman Cousins, who in 1964 was diagnosed with a life-threatening autoimmune disease. 

After being given a 1-in-500 chance of recovery, Cousins created his own laughter therapy program, which he claims was the key to his ultimate recovery. He went on to write the book, Anatomy of an Illness, and established the Cousins Center for Psychoneuroimmunology.

As noted by Medical News Today:

"Over the last few decades, the intriguing and pervasive links between neuroscience and the immune system have slowly been uncovered. What might seem, at first, like an uneasy marriage between the brain and immunity has steadily grown into a fully-fledged interdisciplinary area of study.  This field is known as psychoneuroimmunology (PNI). It is well-established ... that stress can induce illness and that, conversely, a fun-filled occasion with loved ones can soothe aches and pains and stave off the very same illness ... PNI has deep ramifications for the future of medical research, the treatment of diseases and our attitude toward handling stress."

Research conducted in the 1980s and early 1990s revealed that your immune system and brain are actually wired together, and connections between your nervous system and immune-related organs such as your thymus and bone marrow allow for crosstalk between the two systems. 

Revealingly, your immune cells also have neurotransmitter receptors, suggesting that what goes on in your brain impacts your immune system, for better or worse. For example, stress has been shown to reduce activity of virus-fighting immune cells.

Stress also increases levels of antibodies for common viruses such as Epstein-Barr, suggesting that stress can reactivate otherwise latent viruses in your body. Ruminating on a stressful incident has also been shown to increase your levels of C-reactive protein, a marker of inflammation in your body.

Positive emotions also have a decided impact on your health. Steve Cole, Ph.D., a professor at Cousins Center for Psychoneuroimmunology, has done a number of studies investigating the genetic effects of various mental states.

For example, he and his team found that chronic loneliness tends to upregulate genes involved in the regulation of inflammatory response while downregulating genes involved with antiviral control — the combination of which results in decreased immune function. 

In sociable people, the reverse gene activation took place, leading to improved immune function. Other research has shown that happiness optimism, life satisfaction, and other positive psychological attributes are associated with a lower risk of heart disease.

In one of Professor Cole's happiness studies, participants answered questions about the frequency of certain emotional states, covering two different categories or types of happiness known to psychologists as:

• Hedonic well-being (characterized by happiness gleaned from pleasurable experiences, such as sex and shopping) 
• Eudaimonic well-being (originating with Aristotle, this form of happiness comes from activities that bring you a greater sense of purpose, life meaning, or self-actualization) 

Interestingly, while both are positive emotional states associated with happiness, the gene expressions they produced were not identical. 

Those whose sense of happiness was rooted in the eudaimonic camp had favorable gene-expression profiles, while hedonic well-being produced gene profiles similar to those seen in people experiencing stress due to adversity. 

Professor Cole's theory as to these differences is that when you're driven by materialistic values, your happiness depends on circumstances that may or may not be within your control. If you run into adversity, it can cause a great deal of stress because it impedes your perceived ability to be happy.

On the other hand, those driven by a sense of "purpose" are largely buffered against the uncertainty that comes with adversity, and their happiness is not dependent on having or experiencing anything in particular that can at any moment be taken away.

In a similar way, research has shown that different types of stress alter different parts of your immune system. 

• Brief stress, such as making a speech or taking a test, tends to suppress cellular immunity (acquired immunity mediated by antigen-specific T-cell lymphocytes; involved in resistance to infectious diseases) while preserving humoral immunity (which refers to antibody production and accompanying processes). As a result, you may find yourself more vulnerable to the common cold or flu. 

• Chronic stress such as caring for a partner or parent with dementia, suppresses both components of the immune system, making you more susceptible not just to infectious diseases, but all
• The bottom line is this: Be happy whether you like it or not.