Carrying too much body weight can do real damage to your knees — and set you up for a world of pain. Here's why.

If you've ever loaded your car's trunk with heavy objects or driven with four adult passengers, you may have noticed that the ride wasn't as smooth. Your car's shock absorbers probably didn't soak up the jolts from the bumps and the potholes as well as they would have with a lighter load.

Similarly, if you're carrying too much weight on your body, your knees may also be in for a rough ride. The bones that meet in your knees are covered with cartilage, which provides a smooth, gliding surface for the thigh bone, shinbone, and kneecap as they move around within the joint while you walk. When you weigh more than you should, you're putting more force on that cartilage. A variety of studies have found connections between carrying extra body weight and having knee pain. And, in many cases, a condition called osteoarthritis is the link between them.

The Link Between Weight and Knee Pain 

In a recent study, researchers looked at the link between body mass index (BMI) changes and knee pain in 594 women over a 14-year period. They found that the women with higher BMIs were more likely to have knee pain by the end of the study. In another study, researchers in the Netherlands took X-rays of people's knees, then repeated them more than six years later. Those with a BMI over 27 were three times more likely to develop knee osteoarthritis. As an example, a woman who is 5 feet 6 inches tall and weighs 167 pounds has a BMI of 27.

Carrying extra body fat may also lead to the releases of a hormone called leptin, which some experts think may play a role in the development of osteoarthritis. In addition, body fat can release substances that promote inflammation in your body. Two of these, called tumor necrosis factor alpha and interleukin-1, appear to play an important role in the cartilage damage seen in osteoarthritis.

Manage Extra Weight to Help Knee Pain

Here's the good news: In a recent study of overweight and obese people with knee osteoarthritis, those who lost weight with diet and exercise reduced their knee pain by about half. Losing weight is an important part of keeping your knees healthy.

The National Institutes of Health recommends the following steps for exercising safely with knee pain.

• Get a consultation . Talk to your doctor if you have any chronic health problems or you're worried that exercise might cause an injury. If you already have knee pain, discuss types of activities with your doctor that might be safe for you.
  
  

• Exercise. Good types of exercises for heavier people include walking — even for just a few minutes when you're starting out — bicycling indoors or outside, and strength training to build stronger muscles.
  
  

• Be more active. Simply work more physical activity into your daily routine. Walk around while you're talking on the phone (after all, that's why they're cordless!), play actively with your kids or grandkids, and make personal visits at work instead of using e-mail.
  
  

Weight loss is something you can do on your own, says Shook. It's inexpensive. And it might save you from knee surgery or other health problems down the road.