Sitting for a long time left foot numbness may be a normal physiological phenomenon, may also be caused by lumbar disc herniation, cerebrovascular disease. 1. Physiological phenomenon: If it is a bad sitting posture, such as sitting on the left side or crossing the legs, this situation will lead to local nerve compression, affecting blood circulation and numbness of the left foot, which is a normal phenomenon. 2. Lumbar disc herniation: the sensory nerve innervating the left leg is issued from the lumbar vertebrae, so if you suffer from lumbar disc herniation, it may compress the nerve root, causing numbness of the left leg and foot, and sometimes it may be accompanied by pain. 3. Cerebrovascular disease: especially cerebral infarction, static onset of disease, so long time sitting for a long time after the sudden onset of disease, numbness and weakness of the limbs on the side of the symptoms. See in hypertension, diabetes and other chronic diseases of the elderly patients. Sitting for a long time left foot numbness, if self-adjustment can not be significantly restored, should be as soon as possible to consult a doctor, a clear diagnosis, the correct treatment.