Edema can result from congestive heart failure, certain types of kidney disease, and having too little thyroid hormone, among other things.

A: I get more and more questions about this issue. Although this may be coincidental, it may also be related the growing problem with obesity and increased consumption of salt.

Whenever you get swelling that comes and goes over hours or days, it's almost always due to fluid collecting in the tissue right under the skin. The medical term for this is edema. It is very common, especially as we get older.

The two most common places to develop edema are around the eyes and in the lower legs. However, a lot of fluid can end up in the abdomen without the person being aware of it.

Because of the effect of gravity, the edema and swelling around the eyes increases while one is lying down. Many people have "bags" under their eyes when they wake up. Within a few hours the bags go away or greatly diminish in size.

Edema around the eye occurs in many people without any evidence that there is an abnormal source of the fluid. It then can be considered "normal" for that person. But it may also indicate a problem somewhere else.

Overweight Creates an Additional Burden

The next most common place for edema to show up is, as in your case, the lower legs. And also because of gravity, the edema in this area increases after prolonged standing or even sitting. If it becomes bad enough, you can push your finger into swollen skin and leave a pit when you remove your finger. This is called "pitting edema."

Edema in the lower legs is one of the earliest signs of diseased leg veins, such as occurs in varicose veins or blood clots in the veins. Being overweight creates an additional burden caused by the pressure of increased fat in the legs.

Edema can also result from congestive heart failure, certain types of kidney disease, and having too little thyroid hormone. Drugs, such as nonsteroidal anti-inflammatory drugs and some calcium antagonists, can cause ankle edema. Also, for chair-bound people, inactivity and compression on the back of the legs can cause leg edema.

The most common cause of fluid retention, with or without edema, is high amounts of salt in the diet. And high salt diets worsen the edema from all other causes, especially heart disease.

Detective Work Needs to Be Done

Edema is a symptom rather than a disease, so some detective work needs to be done to determine the cause of your edema. And, as is often the case in medicine, this requires ruling out other potential causes.

Ask your doctor about the cause of your edema and whether it is due to any of the diseases I've listed. And make sure that you understand the recommended treatment, if any. Diuretics are the most commonly prescribed drugs for edema, but they may not improve the underlying cause.

Regardless of the cause, also make sure to talk about the amount of salt (sodium) in your diet. Discuss the importance of keeping your legs elevated to help get the fluid flowing out of the legs and into the general circulation. This fluid will eventually reach the kidneys and some of it will be urinated out.