Running can be hard on the knees, but the same may not be true for the hips. In fact, running might protect the hip joint.
New research has shown that running decreased the chance of developing osteoarthritis and the need for hip replacement.
The risk for osteoarthritis did not increase as runners covered more mileage, even if they ran multiple marathons.
Consistent runners tend to have a lower body mass index (BMI), or measure of height and weight together.
The study, led by Paul Williams, PhD, researcher in the Life Sciences Division at Lawrence Berkeley National Laboratory, involved about 75,000 runners and 15,000 walkers over a seven- and six-year period, respectively.
The study is part of the National Runners' and Walkers' Health Studies launched by Dr. Williams in 1991 with follow-up questionnaires given between 1999 and 2002.
Participants were surveyed on the distance they ran or walked and their body weight, height and waist size.
During the follow-up period, participants reported whether their doctor diagnosed them with osteoarthritis and if they had a hip replacement.
Osteoarthritis is the leading cause of disability in the elderly.
During the study period, 2,004 runners were diagnosed with osteoarthritis by their doctors and 259 had hip replacements. At the same time, 696 walkers were diagnosed with osteoarthritis and 114 received a new hip.
Researchers found that compared to more sedentary individuals, runners who covered 1.2 miles per day had a 15 percent lower risk of osteoarthritis and a 35 percent lower risk of needing a hip replacement.
Having a lower BMI can make runners prone to certain injuries, but researchers found that running reduced the chance of getting injured from having a lower BMI.
Participants with a higher BMI at the start of the study were likelier to have osteoarthritis, researchers said. The risk increased 5 percent for each extra kilogram per square meter increase in BMI.
A higher BMI was also linked to hip replacement. This risk increased about 10 percent for each kilogram per square meter increase in BMI.
"In addition to promoting weight loss directly, running attenuates middle-age weight gain, such that higher mileage runners gain only half as much as low mileage runners," researchers wrote in their report.
"The prevention of weight gain is an additional mechanism for limiting risk of [osteoarthritis] and hip replacement risk."
Compared to non-running exercises, running was associated with a lower risk for osteoarthritis and hip replacement. People who played soccer had a 29 percent chance for injury on average, compared to 14 percent for running on average. Weight lifters had a 31 percent chance of injury on average.
According to the researchers, these findings might not apply to elite athletes. But recreational runners may find the exercise preferable to other kinds.
The authors noted that they relied on doctors' assessments in diagnosing osteoarthritis and hip replacement instead of looking at medical images. They also had a greater proportion of runners in their study compared to walkers.
The study, which was funded by the National Heart, Lung, and Blood Institute, was published January 31 in the journal Medicine & Science in Sports & Exercise.
No conflicts of interest were reported.