If you start to notice that your legs are expanding in size, it could be related to the health of your thyroid. Legs swell because of an accumulation of fluid in the tissues. This occurrence is called peripheral edema. There are several causes of this symptom like salt retention, cellulitis, congestive heart failure, pregnancy, venous insufficiency, and side effects from medication.
An edema is a sign of smaller issues like blood clots in the leg, liver disease, kidney disease, lymphedema, or eosinophilic fasciitis. Simple lifestyle changes, such as exercise, eating whole foods and taking supplements can often take care of leg swelling. If the problem persists for long periods of time, do consult your doctor.