It can sometimes be a mystery. You speak to people in their thirties who are suffering from arthritis but others in the seventies are happily going about their business without the inconvenience of this condition. So exactly what causes arthritis?

First of all we have to be clear about what type of arthritis we are talking about because there are several different types with different symptoms. We'll concentrate on osteoarthritis as this is the most common condition and most people will know somebody who suffers from it to a greater or lesser degree.

Doctors do not know the precise causes but they are able to identify a number of risk factors for getting the condition. Here are some of those factors:

Age - We are more likely to suffer from arthritis the older we get. The cartilage that protects the ends of the bones in a joint becomes thinner in sufferers and less able to repair itself. The condition is sometimes referred to as a 'wear and tear' disease.

Injury - It has been found that osteoarthritis can develop in joints that have been previously affected by injury. But just because you have had a broken bone or other injury it doesn't mean that you are going to get arthritis in later life.

Weight - being overweight can put more stress on the weight-bearing joints of the body such as the knees and hips. These are frequently affected by arthritis and many doctors would recommend that overweight sufferers try to lose some weight if possible

Sport - There is a paradox here. Playing sport can have many beneficial effects to us all, including people with arthritis. But high impact sport at a professional level has also been implicated as a possible cause of arthritis. The twisting motion on the knee in sports like soccer, or the constant pounding of the jogger running 50 miles a week could be a contributory factor in developing arthritis. Less intense activities such as swimming are less likely to cause such problems.

Occupation - The occupation that you have performed for years may also be telling. Physical jobs such as building site laborers are more at risk. Assembly line workers who perform repetitive tasks can also be more likely to suffer.

Although it is not always possible to exactly pinpoint the causes of arthritis, it is useful to know the risk factors so that we can take action to reduce the risk of getting the disease.