Can love help you live longer?

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(MoneyWatch) You've probably heard it before -- love, marriage and sex can help you live longer. But is that really true, or is it just a coincidence, something scientists call correlation?

One example of correlation would be if your longevity was influenced by eating a healthy diet, keeping your weight at a healthy level, exercising and being socially connected, and then if you did all these things it just so happened that you're more likely to be in a happy, married relationship. In other words, people who are expected to live longer are also more likely to be in a healthy relationship, not the other way around.

So let's dig down into this question of causation versus correlation. One piece of advice we've heard is that if you're married, you'll live longer. But according to psychology professors Howard Friedman and Leslie Martin, authors of the recently released book "The Longevity Project," that's not necessarily the case for everyone. That's because while research has found that being in a happy marriage tends to help men live longer, it doesn't give the same boost to women, who are more likely to form supportive relationships beyond their partner that can be just as fulfilling as being married. And from a longevity perspective, you're better off not getting married at all compared to living in a unhappy marriage.

"The Longevity Project" focuses on the personality traits that lead to long life. Research behind the book found that a leading indicator is conscientiousness. This makes sense, because conscientious people are more likely to take the steps needed to improve their health, and are also less likely to engage in risky activities such as smoking, drinking excessively, abusing drugs or driving too fast. And I'm guessing it's possible that conscientious people are more likely to have happier marriages, better friendships and healthier work environments.

Other personality characteristics associated with longevity include the ability to laugh, along with people who are socially connected, optimistic, happy and extroverted. It seems to me that this may also describe people who are more likely to be in happy and healthy relationships.

Other health benefits that are correlated with loving and caring relationships include a stronger immune system, faster healing, better cardiovascular health, and less depression and substance abuse. But it's still not clear if the loving relationship causes these beneficial outcomes or if people with all these characteristics are more likely to be in a satisfactory relationship.

Then there are claims and evidence that more frequent sex boosts health and longevity. But are healthier people more likely to have sex, or does having sex make you healthier?

The question of whether such links are causally related or merely correlate is unlikely to be resolved anytime soon.  So if you're the type who needs irrefutable scientific evidence as the foundation for your decisions, you won't be satisfied by the findings discussed above.

With this subject, however, I have a different way of making decisions, which I call the "feel good" method. It feels good to eat right, exercise, be in a loving and caring relationship, and have a robust social life. Feeling good must be beneficial for my health and longevity. If these actions actually help me be healthier and live longer, that's just icing on the cake.

So on Valentine's Day, go out to dinner with your sweetie, exchange some thoughtful notes or gifts, and joyfully indulge in whatever activities follow. You'll certainly feel good, and who knows? It might help you live longer.

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    Steve Vernon helped large employers design and manage their retirement programs for more than 35 years as a consulting actuary. Now he's a research scholar for the Stanford Center on Longevity, where he helps collect, direct and disseminate research that will improve the financial security of seniors. He's also president of Rest-of-Life Communications, delivers retirement planning workshops and authored Money for Life: Turn Your IRA and 401(k) Into a Lifetime Retirement Paycheck and Recession-Proof Your Retirement Years.