ANN ARBOR—Young and middle-aged overweight women with high bone density have an increased risk of developing osteoarthritis during the mid-life, according to a study from the University of Michigan School of Public Health. Osteoarthritis is a major chronic disease estimated to afflict one in 10 people at age 50 and one in two people at age 75.

“Our study supports what researchers have suspected,” said MaryFran Sowers, U-M epidemiologist and principal investigator. “People with increased bone density are more susceptible to osteoarthritis. The ‘stiffer’ bone does not deform, or ‘give’, and then bounce back, so the articular cartilage suffers more wear and tear, which eventually leads to osteoarthritis. Overweight women are at even greater risk because they carry a heavier load.” The U-M study appears in the January issue of the American Journal of Epidemiology.

The researchers collected a range of data on 573 women ages 20-40, including bone mineral density in the spine and hip, X-rays of the hands and knees, body mass index, age, blood pressure, physical activity, smoking and drinking habits, hormone levels and hormone replacement therapy. The researchers found that:

–Factors associated with hand osteoarthritis included older age, being overweight (greater body mass index), higher bone mineral density and increased blood pressure.

–Factors associated with knee osteoarthritis included knee injury, being overweight, higher bone mineral density and increased blood pressure.

–Women with higher testosterone levels “associated with more lean muscle mass” were less likely to have hand osteoarthritis.

–Women in the upper quartile of systolic blood pressure levels were at significantly increased risk of both hand and knee osteoarthritis. The reason for this is not currently known.

–Estradiol levels were not related to either hand or knee osteoarthritis. Estradiol is one of the body’s three major estrogens.

–Women on hormone replacement therapy (HRT) were also slightly more likely to have knee osteoarthritis compared with menstruating women, “but it is likely that HRT simply means that the women were older, and thus more likely to develop the ailment due to age-related factors,” Sowers said.

–Moderate drinking reduced the risk. “Women who were moderate drinkers were less likely to have hand osteoarthritis compared with both non-drinkers or heavy drinkers,” Sowers said.

–Injury contributed to developing the ailment. Women with hand injuries had 4.2 times the prevalence of hand osteoarthritis while women with knee injuries had 3.4 times the prevalence of women with no injuries.

–Smokers were at slightly less risk of osteoarthritis. “Smokers may have less total body mass and would tend to have less bone density. They also may have subtle differences in hormone status or insulin levels. Osteoarthritis may be the only disease for which smoking is a protective factor,” Sowers added.

Sowers’ colleagues for the study include Marc Hochberg of the School of Medicine, University of Maryland; Jeffrey P. Crabbe, Department of Radiology, U-M Medical School; and Anthony Muhich, Mary Crutchfield and Sharon Updike of the Department of Epidemiology, U-M School of Public Health.