THURSDAY, July 27 (HealthDay News) -- The drop in estrogen levels that occurs with menopause may boost a woman's risk for osteoarthritis of the knee, new research suggests.
"Osteoarthritis has always been regarded as a wear-and-tear phenomenon that's really related to biochemical stresses," said study author MaryFran R. Sowers, a professor in the department of epidemiology at the University of Michigan in Ann Arbor.
"But this work suggests that we should expand our thinking to include how hormones might affect the tissues around the joint and change the susceptibility to developing osteoarthritis," said Sowers.
According to the U.S. National Institutes of Health, more than 20 million American men and women have osteoarthritis, making it one of the most common causes of adult disability in the United States.
Reporting in the August issue of Arthritis & Rheumatism, Sowers' team focused on declining blood levels of the estrogen known as estradiol.
Estradiol is the main estrogen in both premenopausal women and women who are in the transitional or perimenopausal phase immediately preceding menopause.
Levels of estradiol and its byproduct hormones, such as 2-hydroxyestrone, are known to diminish once menopause begins, the researchers said. They also noted that while risks for osteoarthritis rise for both genders after age 45, the disease is much more likely to affect women than men.
In their Michigan-based study, Sowers' team spent three years observing the onset of knee osteoarthritis among 842 white and black women between the ages of 26 and 54.
More than 75 percent of the women were premenopausal at the start of the study, with the remainder being perimenopausal.
None of the patients were on hormone replacement therapy prior to the study launch. More than 10 percent of the women had already been diagnosed with knee osteoarthritis before participating in the study.
The researchers assessed the women for their body mass index, and all underwent X-rays of both knees during each year of the study. Blood and urine samples were drawn as well to assess levels of estradiol and other hormones.
The researchers found that those women who went on to develop knee osteoarthritis for the first time during the study period were more likely to have had lower estradiol levels at the start of the study than those who did not develop osteoarthritis.
These same osteoarthritis patients were also more likely to have lower levels of 2-hydroxyestrone, as well.
In both cases, women with knee osteoarthritis were more likely to fall into the bottom one-third of the group in terms of their blood levels of these hormones.
The authors concluded that hormonal drops which commonly occur in perimenopausal and menopausal women are "strongly associated" with the onset of osteoarthritis.
However, they cautioned that it' not yet clear whether these hormonal dips help cause osteoarthritis or osteoarthritis-linked pain and inflammation.
Sowers and her colleagues also found that heavier women were more likely to have lower 2-hydroxyestrone levels. In addition to the well-established notion that excess pounds can aggravate joint stress around the knee, ankle and foot, being overweight might also negatively impact on hormonal levels, which could in turn provoke the onset of osteoarthritis, the researchers said.
Sowers stressed the findings don't mean menopausal women need to seek medical help -- such as hormone replacement therapy -- at this time.
"I don't think that this work suggests an immediate intervention," she said. "I think this work opens and broadens the way we think about the development process for osteoporosis, but I think to talk about doing things based on this would be premature."
Dr. Ronald Moskowitz, immediate past president of the Osteoarthritis Research Society International, agreed.
"This is not a simple connection," he said. "It's a very interesting observation, but one needs to looks at confounding factors in trying to explain the hormonal relationship."
"For example, as women grow older, they age, and their estrogens go down as they become postmenopausal," added Moskowitz, who is also a professor in the department of medicine at Case Western Reserve University Hospitals in Cleveland. "So, the onset of arthritis may be a function of age rather than estrogen level dropping. It may not be causal. It may be simply that age is the risk factor for osteoporosis."
For more on osteoarthritis, visit the U.S. National Institute of Arthritis and Musculoskeletal and Skin Diseases.
By Alan Mozes
SOURCES: MaryFran R. Sowers, Ph.D., professor, department of epidemiology, University of Michigan, Ann Arbor, Mich.; Ronald Moskowitz, M.D., professor, department of medicine, Case Western Reserve University Hospitals, Cleveland, and immediate past president, Osteoarthritis Research Society International; August 2006 Arthritis & Rheumatism.
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