Gout is caused by a build-up of uric acid in the blood. Uric acid is a waste product that forms when the body breaks down chemicals in the cells known as purines.
Most uric acid is removed from the body through the kidneys. A small amount is removed through the digestive system.
Uric acid usually remains dissolved in your blood and passes through your kidneys into your urine so it can be passed out of your body.
If you produce too much uric acid or excrete too little when you urinate, the uric acid will build up and may cause microscopic crystals to form, usually in a joint or surrounding tissue.
The crystals may spill over from the joint cartilage into the joint space where they trigger a reaction from the soft lining (synovium), which produces the intense pain and inflammation associated with gout.
Some things can increase the amount of uric acid in your blood, making you more likely to develop gout. These risk factors fall into one of two categories:
- medical conditions known to increase levels of uric acid, such as obesity, high blood pressure (hypertension), high lipid levels and long-standing impairment of kidney function
- lifestyle factors, such as diet or certain types of medication that you may be taking
These risk factors are discussed in more detail below.
Certain types of medication can increase your uric acid levels and your risk of developing gout. These include:
- diuretics, used to treat high blood pressure (hypertension) or an abnormal build-up of fluid in your body
- niacin, used to treat high cholesterol
Men are more likely to develop gout than women because their uric acid levels rise during puberty. During the menopause, women experience a similar, albeit smaller, rise in their uric acid levels. This explains why symptoms start later in women than in men.
Foods naturally high in purines include:
Alcoholic drinks raise the level of uric acid in the blood by increasing its production in the liver and by reducing how much is passed out in urine.
Beer and spirits do so more than wine, and beer also contains significant quantities of purines. (Moderate consumption of wine - one or two glasses a day - should not significantly increase your risk of gout).
Research has shown a possible link between gout and certain sugary drinks.
Specifically, a study found that men who regularly drank sugar-sweetened soft drinks and drinks with high levels of fructose (a naturally occurring sugar found in many fruits) had an increased risk of gout.
Diet soft drinks were not found to increase the risk of gout.
Studies have shown that gout often runs in families. Around one-in-five people with gout have a close family member who also has the condition.
Medical conditions that can increase your risk of developing gout include:
Gout attacks occur most frequently in the joints of the feet and hands, possibly because the temperature in these joints is often lower than the rest of the body, which increases the likelihood of crystals forming.
It is still uncertain why some people are more susceptible to crystal formation and gout than others with equally high blood levels of uric acid. Many people with a high level of uric acid in their blood and tissues never develop gout.
One theory is that certain genes you inherit from your parents may make you more likely to develop gout by causing your kidneys that are otherwise healthy to be relatively inefficient at excreting uric acid. Several genes have recently been identified that are associated with high uric acid levels and gout and which influence uric acid elimination by the kidney.