Osteoarthritis

Description

Risk Factors

The prevalence in osteoarthritis increases as people age, and in the US about 60% of people over 65 have some form of arthritis. Osteoarthritis and other arthritic conditions affect about 70 million American adults--about 21 million of whom are over 65 years old. With the growing population of older adults, experts expect that the number of arthritis sufferers will double by 2030.

Gender

Before age 45, osteoarthritis occurs more frequently in males (although it is not even common in younger adults). After age 55, it develops more often in females. In a 2000 study, 33% of women had osteoarthritis compared to 25% of men. Some research suggests that women may also experience greater muscle and joint pain, in general, than men. And women also tend to be undertreated for pain compared to men. The causes of such differences in pain sensitivity and treatment are largely unknown and most likely are due to a complicated mix of biologic, psychologic, and social factors.

Education

The incidence is highest in lower educational levels. In a 2000 study, 41% of adults with less than a high school education had arthritis compared to 21% of college graduates.

Geography

Although the average rate of osteoarthritis among older adults in the US is 60%, it can vary widely in certain geographical regions. In the US, the rates in older adults are lowest (34%) in Hawaii and highest (70.3%) in Alabama. In general, the highest prevalence of arthritis in America occurs in the central and northwestern states.

Ethnicity and Inheritance

The rate of osteoarthritis varies by ethnic group. In the US, Caucasians and African-Americans have higher rates of arthritis than Hispanics or other ethnic groups. Osteoarthritis also tends to favor specific joints over other in certain ethnic groups. The following are some examples:

• Studies report that in the US, older African American men are about 33% more likely than Caucasian men to have hip osteoarthritis. And, in one of the studies, although men in both groups had equal risks for arthritic knees, African American men were more likely to have arthritis in both knees and to have more severe cases. Although comparable disparities in knee arthritis were observed between African American and Caucasian women, they might be explained by greater average weight among African American women. The study could not account for the differences among men, however.
• Asians appear to have a higher incidence of osteoarthritis in the knee, an equal risk for osteoarthritis in the spine, and a lower risk for osteoarthritis in the hips than Caucasians. (Because osteoarthritis in the hip is the most common location, Caucasians have a total higher risk than Asians.)

Some researchers stress the need for more research. For example, genes that determine the angles, amount of force, and other structural factors in the hip joints or genes that regulate the chemistry in the joints may account for ethnic differences.

Physical and Anatomical Factors

Some researchers suggest that a number of people have anatomical abnormalities, such as mismatched surfaces on the joints, which could be damaged over time by abnormal stress. Legs of unequal length or skewed feet can cause jerky movement and may induce osteoarthritis. One study reported that those whose knees bent inward (knock-kneed) or outward (bow-legged), for example, were more likely to have progressive osteoarthritis of the knee.

Obesity

Obesity, which is defined as being 20% over one's healthy weight, places people (particularly women) at increased risk for osteoarthritis. It also exacerbates osteoarthritis once deterioration begins. This higher risk is most likely to be due to increased weight on the joints. However, being obese also increases the risk for osteoarthritis in the fingers as well as the knees and hips, suggesting that being overweight may contribute to osteoarthritis in other ways.Some research is now indicating that obesity may produce an inflammatory response, which is now a major suspect in age-related diseases--not only osteoarthritis, but heart disease as well. [SeeWell-Connected Report #53 Weight Control and Diet.]

Work and Leisure Factors

Because injuries can trigger the disease process, people whose work or leisure activities place them at risk for muscle and joint injuries may face a higher risk for osteoarthritis later on.

Workers at Higher Risk. Certain occupations that require repeated stressful motions (such as squatting or kneeling with heavy lifting) can contribute to deterioration of cartilage. A 2000 study suggested that workers whose jobs require kneeling or squatting for more than an hour a day are at high risk for knee osteoarthritis. (In the study, jobs that involved heaving lifting, climbing stairs, or walking also posed some, but not as high, a risk. Being heavier compounded the chances for osteoarthritis.)

People Who Engage in High-Intensity Exercise. There has been some question about the role of strenuous exercise in osteoarthritis.Sports that definitely pose a higher risk for osteoarthritis are those that require repetitive or direct joint impact (such as football), twisting, or both (baseball pitching, soccer).

Marathon runners, however, have a relatively low rate of osteoarthritis in general. Some scientists speculate that running enhances cartilage health because the rhythmical compression of cartilage expels wastes and promotes absorption of nutrients. (One study did report a higher rate of osteoarthritis in marathon runners, which was associated with a higher intensity of impact rather than with the distance being run.)

In any case, regular and moderate exercise is important for everyone and does not increase the risk for osteoarthritis. Furthermore many factors associated with a sedentary life--muscle weakness, obesity, and low lung capacity--are associated with a high risk for osteoarthritis.