- Wearing high heels puts extra pressure on the inside of woman's knee, upping her risk for osteoarthritis later in life.

- Heels also alter muscle and tendon structure.

- If you choose to wear heels, try not to wear them all the time and do regular stretching.

Women commonly sacrifice comfort for fashion, but their choices in footwear may be causing long-term damage to their bodies, suggests a new study.

Wearing high heels, the study found, puts extra pressure on a woman's knee joints, increasing her risks for joint degeneration and osteoarthritis. As low heels become high stilettos, those risks grow.

"Everyone knows that high heels are bad for you," said Danielle Barkema, a biomechanist who conducted the new study at the Iowa State University in Ames. "Wearing even higher heels puts individuals at even greater risk of developing knee osteoarthritis later in life. It can get to the point where there's bone-on-bone contact, and knee replacements are in order."

Compared to walking barefoot, previous research found, wearing heels adds greater compression to the inside of a woman's knee. To expand on the work, Barkema and a colleague compared flat shoes with 2-inch heels and 3.5-inch heels.

In their lab, the researchers used sensors, cameras and other equipment to measure the forces and shock waves in the legs of women, ages 18 to 40, as they walked in each type of shoe.

The women performed a series of trials at either their own chosen speed or at a pre-determined fixed speed. The goal was to get around the natural tendency for women to walk slower in heels and the influence that might have on physical loads and walking style.

Among the results, the study found that wearing heels changed women's posture, caused their ankles to tilt inward and destabilized their ankle joints. There was also significantly more loading on the inner knee, which was even greater in the higher heel.

NEWS: King Tut Wore Orthopedic Sandals

This type of inner knee pressure, called medial loading, is a known risk factor for joint degeneration and osteoarthritis. Barkema will present her results in more detail at a meeting of the American Society of Biomechanics later this month.

The study doesn't mean that everyone who wears high heels will end up with arthritis in their knees, she said. But the results do add to accumulating evidence that high heels just aren't very good for the body.

In a study published last month in the Journal of Experimental Biology, scientists in the United Kingdom found that women who wore high heels five times a week for two years had calf muscles that were 13 percent shorter and Achilles tendons that were substantially stiffer and thicker than those of women who wore flat shoes. The distance the high-heel wearers could flex their feet up and down was also drastically reduced.

The study explains why habitual heel-wearers might feel calf pain when they try to walk barefoot, said study author Marco Narici, of Manchester Metropolitan University in the U.K. Regularly wearing heels, he added, could also make women less efficient at more flat-shoed activities, like running.

"It would be very impractical to recommend that women stop wearing high heels; it would never work," Narici said. Instead, he recommends regular stretching exercises, like standing with your toes on a step and letting your heels drop down.

In the meantime, researchers are narrowing in on what makes for a perfect shoe. In a study published earlier this year in the journal Arthritis Care & Research, rheumatologist Naija Shakoor of Rush University Medical Center in Chicago and colleagues found that walking barefoot or wearing flat, flexible shoes were best for knee joints. In the study, flip-flops and basic sneakers put lower loads on the knees than did clogs or running shoes with added stability. She also recommends arch support.

"It's just common sense that high heels are bad for women," said Shakoor. "I would save them for social occasions and going out. For every day, light, flexible and flat is the way to go."