En español | No one is immune to stress, including me. For my television show, I participated in a stress experiment by wearing a portable device that monitored my heart rate, respiratory rate, and skin temperature for 24 hours. Even after two years of hosting my own show — and two decades of performing heart surgery — I learned I still experience "pre-game jitters." My adrenaline starts to pump, causing my heart to race before it returns to baseline.

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Periods of brief stress like this are normal, but chronic stress takes a toll on the body — there's the rush of adrenaline that never quite turns off, leading to an overproduction of another stress hormone, cortisol. I've seen firsthand how excess cortisol places a massive strain on the heart.

Now scientists are learning how cortisol affects the brain, too. Researchers recently discovered that the hippocampus — an area of the brain that helps you respond to anxiety-filled situations — appears uniquely susceptible to the negative effects of cortisol. Excess cortisol, they suspect, may suppress neurogenesis, the brain's ability to create and support new brain cells. And that's not good for anyone, especially those over age 50.

So how can you turn off the cortisol? Two key stress fighters are exercise and sex. While exercise increases cortisol in the short term, over time it decreases anxiety and boosts neurogenesis — likely by improving blood circulation to the brain. Even more intriguing, the brain cells created during exercise may be more resilient against future episodes of stress.

Next: The stress-reducing benefits of sex. >>