Leg cramps - Causes 

Idiopathic leg cramps

As the name suggests, the cause (or causes) of idiopathic leg cramps are unknown, although a number of theories have been suggested. These include:

• abnormal nerve activity that may occur when a person is sleeping, which causes the muscle of the leg to cramp
• excessive strain placed on leg muscles, such as when exercising, may cause the muscles to cramp at certain times
• a sudden restriction in blood supply to the affected muscles

Another theory about why older people are particularly affected by leg cramps is that tendons naturally shorten over time as we grow older. Tendons are tough bands of tissue that connect muscles to bone. If the tendons become too short, they may cause the muscles that are connected to them to cramp.

Secondary leg cramps

Causes of secondary leg cramps include:

• pregnancy – it is thought that the extra weight that women have to carry during pregnancy can strain the leg muscles, making them more vulnerable to cramping
• exercise – many people experience leg cramps when resting after exercise
• neurological conditions (conditions that affect the nerves that control your leg muscles) – for example, motor neurone disease (a condition where the nerves in the brain and the spine gradually lose function) or peripheral neuropathy (a condition where the nerves inside the leg are damaged)
• liver disease – once your liver stops working properly, toxins inside the blood can build up, which can make your muscles go into spasm
• infection – some type of bacterial infection, such as tetanus, can cause muscle cramps and spasm
• toxins – high levels of toxic (poisonous) substances in the blood, such as lead or mercury, can cause leg cramps in some people
• dehydration – a low level of water in your body leads to a similar drop in your salt levels, which can trigger muscle cramps in some people

Medications

A number of medications have been known to cause leg cramps in a small number of people. These include:

• diuretics – these remove fluid from the body and are used to treat a number of conditions, such as high blood pressure, heart failure and some types of kidney disease
• statins – these are used to treat people with high cholesterol levels in their blood 
• raloxifene – this is used to prevent osteoporosis (thinning of the bones) in women who have gone through the menopause
• nifedipine – this is used to treat angina and Raynaud’s phenomenon (when the supply of blood to the fingers is restricted)
• nicotinic acid – used in the treatment of high cholesterol

If you are concerned that your medication is causing your leg cramps, contact your GP as your dosage may need to be adjusted. Never stop taking a prescribed medication unless advised by your GP or another qualified healthcare professional who is responsible for your care.