The Medicine Cabinet: Ask the Harvard Experts
Q: I am starting to have knee pain when I climb stairs. I read that being overweight increases the risk of developing arthritis. What’s the reason?
A: Carrying excess body weight definitely affects your chance of getting osteoarthritis, the most common type of arthritis. Osteoarthritis is the deterioration of cartilage, a smooth tissue that covers the ends of bones. When osteoarthritis occurs, the cartilage wears away and the bones begin to grind against each other. When it happens in the knees, stair climbing and walking become painful.
There are two ways that being overweight raises your risk for developing osteoarthritis. First, the extra weight puts additional stress on weight-bearing joints, especially the knees and hips. Second, excess body fat means you are more likely to have higher levels of inflammatory factors which can injure joints.
Let’s look at weight and your knees. When you walk across level ground, the force on your knees is the equivalent of 1.5 times your body weight. That means a 200-pound man will put 300 pounds of pressure on his knees with each step. Add an incline, and the pressure is even greater. The force on each knee is two to three times your body weight when you go up and down stairs, and four to five times your body weight when you squat to tie a shoelace or pick up an item you dropped.
Losing a few pounds can go a long way toward reducing the pressure on your knees — and protecting them. A sustained 10- to 15-pound weight loss in obese young people can translate to a much lower risk of osteoarthritis later in life.
Increasing physical activity has many health benefits and can help you shed weight. But stepping up your exercise alone is rarely enough to help you lose weight. Every pound you’d like to shed represents roughly 3,500 calories. So if you’re hoping to lose half a pound to one pound a week, you need to knock off 250 to 500 calories a day. A good way to start is to try to burn 125 calories through exercise and eat 125 fewer calories each day.
(Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.)