Rheumatoid arthritis (RA) is primarily a disease of the joints, but it's essentially a systemic disease that can cause inflammation throughout the body, affecting the lungs, eyes, skin, heart, and blood vessels.

RA is not related to osteoarthritis, although they share many similar features. Osteoarthritis is the most common form of arthritis and is characterized by the breakdown of cartilage because of wear and tear.  

Although the average age of someone with rheumatoid arthritis is in the mid-60s, the disease often begins decades earlier -- and it can even strike children and young adults.  The average age of onset is between 25 and 50 with most cases occurring when people are in their 20s or 30s.

Men account for 30% of all people who have RA. Researchers think female hormones play a role in the development of the disease, which may explain why more women are affected.

Rheumatoid arthritis is an autoimmune disorder, meaning that it develops when a person's immune system attacks itself, sending white blood cells to healthy tissues -- particularly, in RA, in the lining of the joints.  This process leads to inflammation.

Researchers know that all of this occurs in rheumatoid arthritis, but they don't know what causes it in the first place.

A blood test can detect antibodies often found in people who have RA, but it's not a definitive test for the disease. A diagnosis of rheumatoid arthritis requires a more thorough clinical evaluation that would also include symptoms, physical exam findings, and might also include X-rays, to detect joint damage.

A number of studies indicate that smoking may increase your risk of rheumatoid arthritis.  According to the Arthritis Foundation, smoking boosts the risk of RA, particularly among people who have a certain specific gene. Smoking also can make RA worse and harder to treat.

Properly managed, rheumatoid arthritis is not considered to be a danger for pregnant women or their babies. Many pregnant women experience an improvement in symptoms; 70% to 75% of mothers-to-be with rheumatoid arthritis have less pain and other symptoms at the end of the first trimester than RA patients who aren't pregnant.

However, pregnant women with RA need to be very careful about medications they take during pregnancy.  Some RA drugs may increase the risk of miscarriage, premature birth, or birth defects. 

Most new mothers with RA experience a recurrence of symptoms in the weeks after pregnancy.

Researchers don't know what causes RA, but they think many factors are involved.  Genes associated with the immune system are thought to play a role; researchers have identified genetic markers associated with a greater probability of developing rheumatoid arthritis. Researchers also think environmental factors -- viral or bacterial infection, for instance -- may help trigger RA (although the disease itself is not contagious).  And scientists think hormones may play a role.

RA affects people differently. Symptoms may wax and wane, but it is a chronic condition.  Most RA patients experience periods of intense disease ("flares") interspersed with periods during which the disease subsides ("remissions").  This combination of flares and remissions is highly variable from person to person: Some people have mild, short flares followed by a long remission; others may have more severe or longer flares that never go away.  Early diagnosis and treatment before destructive joint damage develops  may help put the disease into remission.

Rheumatoid arthritis can be deadly.  People with RA are two times more likely to die than other people of their same age.  Cardiovascular disease is responsible for about half of all deaths among people with RA.

Medications are increasingly seen as having potential to prevent joint damage in newly diagnosed RA patients or to put the disease into remission.  Most patients begin treatment with a DMARD (disease-modifying antirheumatic drug).

Surgery remains a treatment option, but increasingly it’s seen as appropriate for more advanced stages of the disease.

Doctors recommend that RA patients strike a balance between rest and exercise, but physical activity is encouraged. Exercise can help preserve joint mobility and healthy muscle tone.  However, people with RA may need to modify their exercises and other physical activities to adjust to the physical limitations brought on by the disease.

According to the National Institutes of Health, "there is not enough scientific evidence to firmly establish that any [complementary and alternative medicine] therapies are safe and effective for RA."  It warns against replacing proven medical treatment with unproven alternatives.

However, the NIH's National Center for Complementary and Alternative Medicine says some mind-body therapies (such as meditation or tai chi) or supplements (such as fish oil) may be helpful additions to conventional treatment. It cautions, though, that some supplements may interact with medication.

Consult your doctor before starting any alternative treatment.

According to the Arthritis Foundation, "scientific studies have not proved that diet changes either cause or relieve symptoms of rheumatoid arthritis."

However, as the Arthritis Foundation also notes, a wide variety of foods -- "from strawberries to olives to fish" -- have been shown to have anti-inflammatory properties.   It has yet to be proven, though, whether these anti-inflammatory properties have actual clinical benefit for people suffering from RA.