Look Thinner Instantly (cont.)

In fact, she says, when subjects looked only at the bodies of the women, (their heads were masked) the researchers found that the woman who weighed more -- 125 pounds, compared to the 105-pound model -- was perceived as thinner and more attractive simply because she was standing up and taller.

Personal trainer Jessica Bottesch isn't surprised. "When you slump over, you lose inches in your height, so you are taking whatever your body mass is and scrunching it down, making yourself look shorter and wider," says Bottesch, co-owner of Empower Personal Training studios in North Carolina.

But, Fleming says, "when your body is in alignment, your head is sitting squarely on your shoulders, and your shoulders are pulled back with your core muscles pulled in, you not only increase your height and stretch out your body mass, making you look thinner, but you're also projecting an image of confidence, of being more alert, and more youthful -- all of which makes you look more attractive."

Posture and Your Health

If vanity isn't enough motivation to get you to stand taller, experts say posture can also affect your health.

"Low back pain, shoulder pain, neck pain, tension headaches, trigger points in neck or shoulders, sometimes tightness and stiffness -- all of these problems can occur when our skeleton is thrown out of alignment via bad posture," Bottsech says.

In a study presented at the annual meeting of the Radiological Society of North America in 2006, doctors found that the typical "slouch" is linked to higher rates of wear and tear on the spine, which is often a contributing factor to chronic lower back pain.

In another study published in the journal Headache, researchers found that people whose posture caused their heads to jut forward had more frequent, longer, and more severe headaches than people who maintained a correct posture.

But even if you don't experience any short-term health consequences, you may not be off the posture hook.

Over time, studies show, faulty body alignment can lead to actual skeletal damage, including degeneration of the disks and joints, and even a breakdown of cartilage that can leave you achy and less mobile in your later years.

This may be particularly important for women at risk for osteoporosis. In a study published in the journal Bone and Mineral Research in 2006, researchers found that posture that continually causes the head to jut forward (known as hyperkyphotic posture) was linked to a higher risk of fractures in women aged 47-92 -- independent of bone mineral density or even a history of fracture.

The Big Slump: Why Our Posture Is So Bad

Right now, you're probably remembering all those times Mom whispered in your ear "stand up straight". And of course, she was right. But if you're also thinking poor posture is only about what goes on when you're standing, you're missing much off the message. Novak says slumping when we're sitting is by far the more serious problem.