What's black and white, and read all over? Hopefully, this tip. (Everyone knows embarrassed zebras are r-e-d.)

A recent study on humor surveyed people in Switzerland and the U.S. (there's a joke in there somewhere) and found that good-natured humor (e.g., "Waiter, what's that fly doing in my soup?" "The backstroke.") elicits more positive emotions than darker punch lines.

Add to that the newest findings on the power of the smile — the act of smiling, even when it's forced, not felt, lowers your heart rate, and if you're over 40, smiling makes you look a lot younger — and you've got a good case for light-hearted jokes.

So, here's our quiz. Can you identify the positive (boosts mood and optimism) from the more negative (amusing, but not so health-promoting) ripostes.

1. "That's a nice sweater. Too bad they didn't have it in your size."

(Negative. Doesn't help situation)

2. "I just had an MRI to find out if I'm claustrophobic."

(Positive. Relieves stress for those who don't like closed MRIs.)

3. "Yes, Madame, you are ugly and I am drunk. But the difference is that when I wake up in the morning I will be sober."

(Quite negative. Winston Churchill's days as prime minister were numbered.)

4. "That restaurant is so crowded nobody goes there anymore." (Yogi Berra), AND "Time flies like an arrow. Fruit flies like a banana." (Groucho Marx)

(Both positive.)

Our tip? Stick with kind-hearted humor. We know Joan Rivers' fans may disagree, but before you decide the debate for yourself, remember, "It ain't over, 'til it's over."


© 2012 Michael Roizen, M.D. and Mehmet Oz, M.D.
Distributed by King Features Syndicate, Inc.