Systemic Factors May Explain Sex Differences
By Annette M. Boyle
DURHAM, NC – While the commitment to physical fitness demanded of active duty forces can keep many ailments at bay, the rigors of service also bring an increased risk of arthritis and other rheumatic diseases, especially for young women entering (and exiting) the military.
As the major rheumatic diseases disproportionately affect women, the increasing number of women in uniform means military rheumatologists are likely to see many more patients and primary care providers will need to screen for those diseases more aggressively.
In 1980, women accounted for 8.4% of all servicemembers. Today, women make up more than 14% of active duty forces, and 20% of all new enlistees are female. About 10% of veterans are female.
A recent study published in the Centers for Disease Control and Prevention’s Morbidity and Mortality Weekly Report (MMWR) found that nearly one-third of female veterans suffer with arthritis and other rheumatic diseases compared with about one-quarter of male veterans. 1
“We don’t completely understand why women are more likely to develop arthritis,” said study co-author Kelli Allen, PhD, health services researcher and exercise physiologist with the VA’s Durham Center for Health Services R
esearch in Primary Care and an associate research professor at Duke University. “Generally, the highest risk tends to be in post-menopausal women and may be related to the estrogen receptors in cartilage as well as other factors. For both men and women, osteoarthritis in young active duty personnel and veterans is likely related to both injuries and occupational overuse.”
Previous studies have shown a higher rate of arthritis in young servicemembers than in their age-matched civilian counterparts, with about 11,000 new cases diagnosed each year. Those numbers will likely increase sharply as the number of women in the military continues to rise.2
The researchers analyzed data from the 2011, 2012 and 2013 Behavioral Risk Factor Surveillance System (BRFSS) for individuals who self-identified as veterans.
To clarify the use of “arthritis” in the article, the authors noted that “BRFSS respondents were defined as having arthritis if they responded ‘yes’ to the question, ‘Have you ever been told by a doctor or other health professional that you have some form of arthritis, rheumatoid arthritis, gout, lupus, or fibromyalgia?’”
The five conditions were grouped together, as “it’s common to ask this type of question when looking at a big picture public health perspective, since these are all arthritis-related/rheumatic diseases,” Allen explained. While the American College of Rheumatology (ACR) classifies nearly 100 different disorders as rheumatic diseases, osteoarthritis accounts for about 70% of all patients with any rheumatic disorder.
The study updates previous figures which “predate the Persian Gulf War, were small, or studied men only, despite the fact that women comprise an increasing proportion of military personnel and typically have a higher prevalence of arthritis than men,” noted the authors.
When it comes to arthritis, the study found some significant variances between men and women and between veterans and nonveterans. “There’s a very interesting difference in younger age groups, in particular,” Allen told U.S. Medicine. Allen and researchers at the CDC found that arthritis was 50% more prevalent among female veterans ages 20-24 (17.3%) than among male veterans of the same age (11.6%).
That age group also presented the most striking difference between women veterans and nonveterans, with the women veterans having nearly twice the rate of arthritis compared to women who had not been in the military (17.3% and 9.8%, respectively). “In younger women, the difference may be due to more joint-injury exposures among veterans,” Allen said.
Between women veterans and nonveterans, the numbers become more comparable as they get older. Among women over the age of 65, the difference between women veterans and their nonveteran sisters is negligible; 58.9% of the veterans have arthritis compared to 58.2% of those who never served.
The higher rates of arthritis among female veterans compared to male veterans persisted over time, however. In the 45- to 64year-old age group, women veterans had a 40.3% prevalence rate, while their male counterparts had a 36.0% rate. Among veterans over age 65, the spread widened to almost 12 percentage points, 58.9% for women and 47.1% for men.
In the general population, women develop osteoarthritis and rheumatic arthritis at two to three times the rate of men and are 10 times more likely to be diagnosed with fibromyalgia and lupus. Of the five conditions surveyed, only gout is more common in men, in whom it occurs at six times the rate seen in women.
Several hypotheses explain why arthritis and other common rheumatic diseases are more prevalent in women. “There’s a hormonal hypothesis, that inflammation may increase the risk of some types of arthritis and estrogen protects against inflammation. As estrogen levels decrease, inflammation increases and may put women at a higher risk of arthritis,” said Lt. Cmdr. (USPHS) Kamil Barbour, PhD, of the CDC.
According to the ACR, that inflammation, along with “changes in the joints and pain in the surrounding structures,” are not only a factor in osteoarthritis and rheumatoid arthritis but also characteristic of other rheumatic diseases such as gout, fibromyalgia and lupus.
“There’s also a biological hypothesis that attributes the increase in some types of osteoarthritis to varying alignment of the knee joints between men and women. Women’s knee joint are not aligned as straight as men, which can result in greater cartilage resorption and a higher rate of injury per incident,” Barbour noted.
Arthritis and related rheumatic diseases also have a strong genetic component, Barbour told U.S. Medicine. Specific genes have been implicated in rheumatoid arthritis (RA). Lupus, ankylosing spondylitis, another rheumatic disease and rheumatoid arthritis are thought to share a common autoimmune pathogenesis based on genome-wide association studies. Research is ongoing to identify a genetic component to osteoarthritis.3
Prevention and Management
As more servicemembers and veterans develop arthritis and related rheumatic diseases, the VA and DoD are focusing on diagnosing the conditions and working with those who have it to mitigate its impact on their lives.
“In general, we don’t have a good way of screening for arthritis, and when pain is not severe or consistent, it often goes unreported. It’s important to recognize that, as women’s roles in the military have changed, they have increased risk of injuries and arthritis, so physicians need to consider arthritis not only for older male veterans but for younger female veterans, too,” Allen said.
Veterans also can reduce their risk of developing arthritis by taking two steps, according to Barbour. “There are two modifiable risk factors: Maintain a healthy weight with a body mass index (BMI) of 18.5 to 25 and avoid joint injury,” he advises.
The ACR also recommends physical activity as an essential part of fibromyalgia treatment to reduce pain symptoms and fatigue and regular exercise for patients with osteoarthritis and rheumatoid arthritis to maintain mobility and increase muscle strength, which can reduce pressure on the joints. Lupus patients are advised to exercise regularly, but not intensely, and to take frequent breaks.
“Another big piece is helping people rehabilitate well if they are injured. For veterans, that can mean engaging them in healthy lifestyles so they maintain physical activity and avoid the stress obesity places on the joints,” Allen added.
1 Murphy LB, Helmick CG, Allen KD, Theis KA, Baker NA, Murray GR, Qin J, Hootman JM, Brady TJ, Barbour KE; Centers for Disease Control and Prevention (CDC). Arthritis among veterans – United States, 2011-2013. MMWR Morb Mortal Wkly Rep. 2014 Nov 7;63(44):999-1003.
2 Cameron KL, Hsiao MS, Owens BD, Burks R, Svoboda SJ. Incidence of physician-diagnosed osteoarthritis among active duty United States military service members. Arthritis Rheum. 2011 Oct;63(10):2974-82.
3 Dieudé P. Rheumatic diseases: environment and genetics. Joint Bone Spine. 2009 Dec;76(6):602-7.