What Causes Varicose Veins?

Whilst arteries carry blood from the heart to the rest of the tissues, veins return this blood from the body to the heart to enable it to be recirculated. This returning blood must be moved upwards from the legs towards the heart against gravity. This is carried out by a combination of muscle contractions that act like a pump, along with a system of one-way valves in the veins that only allow the blood to move upwards (against gravity), thus preventing it from flowing backward.

The valves found in veins consist of small pockets that fill with blood until they are forced together, sealing off any possible backflow of blood. However, when a valve deteriorates it may not be able to make a tight seal. Blood will then seep back into the part of the vein below it, and that part of the vein will swell. The vein will appear blue as it contains deoxygenated blood, which is in the process of being recirculated.

However, this problem does not occur with the body's deep veins. This is because these veins are fully supported by the muscles they run through, and also because they share the supportive sheath of connective tissue of the nearby arteries. Unfortunately, the veins just under the skin have no such support. If the valves allow them to over-fill with blood, then they easily spread and become distorted in shape to produce varicose veins.

Varicose veins tend to run in families, and there is probably a genetic tendency to leaky valves. They may also be brought on by a collection of circumstances, such as pressure at the upper end of the vein from tight clothing or from fat in the abdomen. People who spend a great deal of their time standing or sitting are more at risk of developing varicose veins than those whose jobs involve physical activity.

Pregnancy can also cause varicose veins; this is because the volume of blood in the body increases during pregnancy, whilst the flow of blood from the legs to the pelvis decreases. This circulatory change is intended to support the growing foetus, but can cause the unpleasant side-effect of enlarging the veins in the legs. The condition may be exacerbated during late pregnancy when the uterus exerts a greater pressure on the leg veins.