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When it comes to retirement, good health cuts both ways. As any financial calculator will tell you, living longer actually means you'll need a bigger nest egg. But the healthier you are leading up to retirement, the easier it is to build up the savings you'll need.

A recent National Bureau of Economic Research study by James Poterba, Steven Venti, and David Wise found that people who were among the healthiest 20% in their fifties retired with three times the assets of the least healthy. And the healthy also spent down their wealth more slowly.

Poterba says that's because the impact of health on your finances begins well before you quit working.

"People in good health have lower health care costs, so they have less of a drain on their resources," he says. Also, other research shows that about half of people who retire earlier than they planned cite health as the reason. Staying healthy gives you more power to save for longer.

TAKE ACTION

Know your numbers. According to the U.S. Agency for Healthcare Research and Quality, one-third of adults with diabetes don't know it, and 20% of adults with high blood pressure are unaware. If you haven't been checked for a few years, do so now. Make sure your spouse does too.

Focus on what you can control. Just because you have a family history of a health condition doesn't mean you'll get it as well.

"DNA isn't your destiny," says Laura Carstensen of the Stanford Center on Longevity. "Research shows a very small number of factors make a big difference." Those probably won't come as a surprise: whether you smoke, how much you drink, your weight, and your exercise routine (you've got one, right?).

Any smoking is bad, but how much alcohol or weight is too much? Here's the scoop: No more than seven drinks a week for women or 14 for men, according to the National Institute of Alcohol Abuse and Alcoholism. For weight, check your body mass index at cdc.gov to see if you are in the healthy range.

You don't have to become a triathlete. Just 2½ hours of moderate exercise a week can make the difference, according to the Centers for Disease Control.

Need some extra motivation to hit the treadmill? People who are fit in middle age battle fewer chronic ailments in the last five years of life, so they get to enjoy more of their retirement being active and feeling good.