There are so many things to worry about these days. Wouldn't it be nice to cross something off the list? Turns out you can. Researchers have been busy debunking some common medical myths that have been repeated so many times, people assume them to be true. Here are five misconceptions you can stop biting your nails over now:

1. Myth: Stretching before exercise prevents injury.

Fact: There's no evidence to support the old presumption that holding a stretch for 20 to 30 seconds primes muscles for a workout. On the contrary, we now know it actually weakens them, thanks to a recent University of Nevada report, among other studies. A light, five- to 10-minute jog five minutes before exercise is now recommended.

2. Myth: Eggs raise your cholesterol.

Fact: In the 1960s and '70s, scientists linked blood cholesterol with heart disease and gave eggs a bad rap. More recent studies have found that saturated and trans fats in a diet are more likely to raise heart disease risk, according to the American Heart Association. An egg has only 1.6 grams of saturated fat, compared with about 3 grams in a cup of 2 percent milk. At 213 milligrams of cholesterol, one egg slips under the AHA's recommendation of no more than 300 milligrams a day. Just watch the cholesterol levels in the other food you eat that day.

3. Myth: Cancer cannot be prevented.

Fact: As many as 50 percent or more of cancer deaths in the United States are caused by social and environmental conditions and unhealthy choices, according to the Centers for Disease Control and Prevention. In general, you can help your body prevent cancer if you quit smoking, avoid second-hand smoke, avoid drinking too much alcohol, avoid weight gain, eat five or more servings of fruits and vegetables a day, eat a low-fat diet and be physically active.

4. Myth: Shaved hair grows back faster, coarser and darker.

Fact: A 1928 clinical trial compared hair growth in shaved patches to growth in nonshaved patches. The hair that replaced the shaved hair was no darker or thicker, and did not grow in faster, according to Indiana University School of Medicine researchers who debunked seven commonly held medical beliefs in a 2007 report. When hair first comes in after being shaved, it grows with a blunt edge on top. Over time, the blunt edge gets worn so it may seem thicker than it actually is. Hair that's just emerging can be darker too, because it hasn't been bleached by the sun.

5. Myth: You should drink at least eight glasses of water a day.

Fact: A 1945 article from the National Research Council claimed that a ''suitable allowance'' of water for adults is 2.5 liters a day. The last sentence of the article noted that much of that water is already contained in the food we eat, but most people ignored that fact. Existing studies suggest we get enough fluids from our typical daily consumption of juice, milk and even caffeinated drinks, the Indiana University researchers found.

Get Smart appears every other week, and offers a quick overview of health and medical topics in the news. Got a question or suggested topic? E-mail jmailander@

MiamiHerald.com.

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