The cause of varicose veins is the failure of the leg pump.

This is usually due to the valves failing (see "How Veins Work" later in the Veins Web Site).

Most valves fail in the teenage years - by the time you've got your job that makes you stand up a lot, the writing is on the wall.

Standing still for long periods of time probably does not cause veins - however, if you have lost your valves, then standing is most likely to make both the symptoms and the speed of deterioration of the varicose veins worse.