Richard Branson is a famously active old guy. Despite being 71, the entrepreneur and grandfather can often be found rocketing into space, kite-surfing on his private island, or launching innovative new ventures. On his blog recently, he credited a good portion of his age-defying energy and health to his carefully crafted diet

Eating a lot of kiwis like Branson will certainly do you no harm. And no one would argue that diet plays a huge role in how well people age. But new research suggests Branson might have the aging equation at least partially backwards. Perhaps it's not just that slowing physical aging helps him be so engaged and optimistic. Perhaps it's also that being so engaged and optimistic slows his physical aging. 

Want to live a half a decade longer? 

That's the suggestion of a new study recently published in Health Psychology that analyzed data tracking the physical and mental health of more than 20,000 adults aged 50 or over for 14 years. 

The researchers first sifted through the data looking for all the usual factors that might cause someone to meet an earlier end; things like smoking, existing health conditions, and socioeconomic status. But even when all these known factors were controlled for, the researchers found that some older adults seemed to live longer than their health profile would suggest. What was the magic ingredient keeping this group alive longer? 

The short answer is better psychological well-being. On average those who were happier, more optimistic, and more purposeful lived longer. And not just a little bit longer. "People with significantly higher than average life satisfaction, positive feelings, purpose in life, or optimism at age 50 lived an average of five to eight additional years," reports UC Berkeley's Greater Good Science Center

How does greater mental well-being add half a decade or more to your life expectancy? The design of this particular study means it can't offer definitive answers, but lead researcher Jennifer Boylan has a few ideas. 

"Boylan says people who are psychologically healthy tend to take better care of themselves by being physically active, sleeping better, and engaging in more preventative health care. Also, being mentally healthy might help people cope better with stress, reducing the harmful physiological responses (like increased heart rate or blood pressure) that come with it," reports Greater Good. 

Mental health matters more than we think it does. 

In some ways this finding isn't too shocking. Almost all of us have experienced how poor mental health can impact your stress levels, sleep, and general feelings of physical well-being at one time or another. Of course, mental well-being helps you be healthier and live longer. But as common sense as this effect may be, too many of us underestimate the impact of mental health on physical health and aging. 

Columbia University professor Kelli Harding has written a whole book on this phenomenon called The Rabbit Effect. The book's unusual title comes from a classic experiment in which researchers were trying to determine the effect of high-fat diets on the heart health of rabbits. Unexpectedly, the researchers noticed that one group of bunnies was surprisingly healthy despite their lard-laden diet. What was keeping them healthier than expected? In a word: kindness. This particular bunch of bunnies was being cared for by a big-hearted research assistant who spent extra time cuddling them. Their hearts, literally, noticed. 

This experiment offered scientific proof that social support and happiness have significant,  measurable impacts on our bodies. But Harding notes that people (and policymakers) often ignore this truth when they decide what to prioritize for better health. 

"We spend a fortune on medical care in this country -- far more than other countries per capita. But we're not getting the health results we want ... it's probably because we're really doubling down on medical care and not investing in our social world the way that we could," Harding observes. 

Individuals do the same thing. We worry about eating more veggies or putting in more steps, but forget that while these are great behavior changes, optimism, meaning, and friends matter, too. In fact, they matter a lot, like five to eight additional years worth. 

So if you're looking to stay in the entrepreneurial game as long and as energetically as possible, don't neglect your mental well-being. Doing so not only sets you up for short-term unhappiness, but is also likely to shave years off your life.