Gearing up for a new and improved you in the New Year? It’s great to set physical goals, like losing weight and getting in shape, but you’d be wise to put just as much effort into turning over a new leaf when it comes to your mental health, too.

Many people assume that by middle age, our personalities are set in stone – but a recent study from Stanford University found that the opposite is actually true. In fact, researchers discovered that as we age, we are not only able, but likely, to change our traits and behaviors. Translation: It’s entirely possible to transform from a wallflower into a social butterfly or turn your pessimism sunny-side up. And doing so won’t just make you happier and more connected to others; it’ll actually make you healthier, too.  Here’s the proof – and two crucial changes to make in 2010.

It’s never too late ... to make new friends.

What are friends for? Longevity and better health, for starters. A 10-year Australian study of almost 1,500 people age 70 and older found that those with the largest social circles were 22 percent less likely to die than those with fewer friends. And a new study from Rush University in Chicago found that elderly adults who participated in social activities had better motor function than those who did fewer such activities.

“Friendships are critical to our physical and emotional health, especially as we age. They reduce anxiety and stress, and make us feel more connected to the world around us,” says Irene S. Levine, PhD, professor of psychiatry at the New York University School of Medicine and author of Best Friends Forever: Surviving a Breakup With Your Best Friend (Overlook Press, September 2009).

Make a change: Levine advises connecting with others by pursuing your own interests – think joining a book club or cooking class, volunteering or participating in a civic or religious group. (Not sure where to start? Visit MeetUp.org, a free site where users create or join groups that meet offline to pursue common interests). If you’re not the talkative type, enlist the help of a Chatty Kathy. A recent study from Japanese researchers, in the Asian Journal of Psychology, revealed that shy people were able to successfully able to expand their network by attending events with a social friend.

It’s never too late ... to find happiness

You can learn to see the glass as half full – even if you’ve spent most of your life wondering where the water is. “Research shows that people are able to change their level of happiness to some degree,” says Dilip V. Jeste, MD, Director of the Sam and Rose Stein Institute for Research on Aging and Distinguished Professor of Psychiatry & Neurosciences at the University of California, San Diego. Interestingly enough, it’s not your health or circumstances that matter most. Dr. Jeste recently conducted a study of 500 adults age 60 to 98 who had dealt with health problems including arthritis, diabetes, cancer and heart disease, and found that on average, they rated their degree of successful aging as 8.4 out of 10. The reason? “They had learned to cope, and didn’t view illness as a barrier to happiness,” explains Dr. Jeste. “As we age, it’s almost inevitable to have some physical problems. The question is, how do you manage? The majority of individuals in our study had found ways to improve their quality of life.”

Make a change: Be nicer to other people – and take note of when you do. A study from the University of Michigan and Japanese researchers found that study subjects who kept track of their acts of kindness for just one week reported being happier afterward as a result. Dr. Jeste also suggests increasing both your physical and mental activity level. Not only will you boost feel-good brain chemicals like serotonin, “you’ll reduce stress, which can have a major impact on how happy you are,” says Dr. Jeste.