Michael Edwards

In one study, 94 percent of bills had pathogenic or potentially pathogenic organisms on them. (Interestingly, another study showed 92 percent tested positive for cocaine.) But at the end of the day, are they dangerous? No. Our skin provides a barrier. Just avoid sucking on dollar bills, and do less cocaine, please.

2. What's the popping sound in my hip (or elbow or knee) when I do certain stretches or exercises?

When you stretch a joint, it creates a vacuum that literally sucks gas out of the fluid inside the joint. Pop. No big deal.

3. Does warm water quench thirst as effectively as cold water?

No. Cold water actually slows gastric emptying, and because the water hangs around longer, it gives your stomach time to tell your brain that you're hydrated.

4. When I notice a new problem, how many days should I wait for it to go away before I talk to a doctor?

If you have crushing chest pain that feels like an elephant is sitting on your chest, maybe see a doctor, because you're having a heart attack. Same if you're passing out. But if you've got diarrhea or the flu, two to three days is very reasonable. Five to seven days for a sprained joint.

5. Carrots: honestly good for the eyes or old wives' tale?

Lutein is the best for eyes — and it's in leafy, green vegetables. The carrot rumor was started during the Second World War. The Nazis realized that the British were getting a lot of lucky shots on their aircraft, and so the British started the rumor that their pilots were being given carrots to improve their eyesight. Which was hogwash. What they really did was discover radar.

6. I've had lower-back pain for years. Flares up when I run on concrete, like when I play tennis or basketball. Any athletic shoes or equipment that you can recommend to soften the impact?

You want orthotics. They work. I like Zapz (masterfitenterprises.com).

7. My dermatologist asked me how many sunburns I got before I was 18. Is that when I screwed myself with the melanoma?

We used to think you got most of your UV exposure before age 18. Now we know it's more like 25 percent. But even if you burn once, you increase the chance of developing melanoma. But we're talking about blistering burns, like in The Heartbreak Kid. Not just a little redness.

8. What kind of stories do heart surgeons tell at the bar after work?

It's usually jokes. Medical jokes. "You hear the one about the constipated accountant? Worked it out with a pencil."

9. Are fresh berries healthier than frozen ones?

There's not that big a difference — probably 20 percent — in the nutrient levels. But the good thing about frozen berries is they don't lose those nutrients over time. Net, frozen berries are a great value.

10. My bum knees mean I can't jog. What are your recommended alternatives? And please don't say elliptical machine. Boredom's worse than joint pain.

Elliptical machine. But if you want something more athletic, cycling or swimming are both high-energy and low-impact.

11. When it comes to vitamins and supplements, can there be too much of a good thing?

Yes. Just go with a complete daily multivitamin plus DHA-omega-3 fats. Add some extra vitamin D if the multi doesn't give you the 1,000 IUs (international units) you need.

12. Do women really have smaller bladders than men, and is that why they have to stop to pee every 17 miles?

Yep.

Mehmet Oz is a heart surgeon and the coauthor of You: Being Beautiful.

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