It doesn’t just annoy your friends and co-workers -- it may not be very good for you, either. A substance called synovial fluid keeps your joints moving easily. The sound your knuckles make when they “crack” comes when you pop tiny bubbles in that fluid.

If you do it all t...

This can damage your teeth as well as the skin around your nail bed, which can lead to infection. You also may get more colds and other illnesses when you put your fingers, which often carry germs, into your mouth. It can help to keep your nails neatly trimmed or manicured.

If you don’t get enough sleep, you’re not just turning yourself into a daytime zombie -- you also could be more likely to have high blood pressure, heart disease, diabetes, and depression. And it might be harder for you to learn and remember things. Set a regular sleep routine an...

Sound is measured in decibels -- normal conversation is about 60 decibels.

• It's best to keep the volume in your headphones below 75 to be safe. And don't listen for more than a couple of hours at a time.
• You're more likely to lose hearing as ...

Not waves -- the Internet. The “blue light” given off by electronic gadgets like phones, computers, and TVs can mess up your sleep. And some studies show that too much of any kind of nighttime light might be linked to cancer (especially breast and prostate), diabetes, obesity, and heart disease. ...

Most Americans spend too much time in chairs. Part of the problem is the modern workplace, where you may hunker over your computer for hours on end. This slows down your metabolism, which means you could gain weight. It’s also linked to other health problems, including heart disease.

• ...

If you make a habit of it -- even if it’s healthy food -- you’re likely to gain weight. That can lead to heart disease, diabetes, and high blood pressure, and it can raise your chances of certain kinds of cancer.

• Check portion sizes before meals and measure out snacks...

It can leave you less satisfied -- and make you more likely to overeat over the course of the day. If you slow down, you could feel fuller with less, because your body has a chance to realize you’ve eaten enough. It can help to focus when you eat: Take small bites, and chew them well.

You did a full brush, isn’t that enough? Nope, you need to clean between your teeth, too, if you want to do all you can to get rid of plaque, the sticky bacteria-filled film that causes cavities.

Too much plaque also can lead to gum disease, a serious condition that’s link...

Soda, candy, and pastries have lots of calories and little nutrition, and all that sugar gets into your blood too quickly. Those kinds of things are linked to serious health problems like obesity, diabetes, and heart disease.

• “Complex carbs” with more fiber and nutrit...

It’s not how many people you know or how often you see them -- what matters is that you feel connected to others. If you don’t, you’re more likely to have high blood pressure, depression, brain issues (like Alzheimer’s), and inflammation.