Edema, which can develop in nearly any organ or body region, results from an imbalance in the opposing mechanical and chemical forces that normally keep fluids inside your blood vessels. Much like water traveling through a porous soaker hose, the liquid coursing through your arteries and veins tends to get pushed into the surrounding tissues by hydrostatic pressure within the vessels. Usually, this fluid is drawn back into your circulation by reverse osmotic pressure – a sort of “chemical sponge” – generated by the relatively higher concentration of proteins and electrolytes within the capillaries, where hydrostatic pressures are low. Fortunately, the back-and-forth exchange of fluids, nutrients, gases and electrolytes occurs at an unconscious level; it’s only when this finely tuned mechanism fails that we become aware of our own fluid dynamics.
Simply stated, if the hydrostatic pressure that pushes liquid out of your vessels exceeds the osmotic pressure that pulls it back in, the fluid starts loitering in your tissues, where it eventually becomes noticeable as swelling. In many cases, the feet are the first body parts affected by edema, because they’re located where the hydrostatic pressures are highest. (After all, water follows gravity when it is given the opportunity.)
Most women who have been through a pregnancy are familiar with pedal edema, which is nearly universal during the last trimester. The pedal edema associated with pregnancy is believed to stem from several factors: increased blood volume, compression of the veins that return blood from the legs to the heart, and hormonal changes that increase capillary permeability (leakiness). Although many doctors still tell pregnant women to cut back on salt to relieve foot swelling, elevation of the lower extremities, daily walking (which pumps blood from the legs) and compression stockings are likely to be more useful than salt restriction. Following delivery, the pedal edema associated with pregnancy typically resolves.
There are other times when pedal edema is a transient, benign condition. Individuals who take long trips or who sit for prolonged periods often discover a bit of swelling in their feet and lower legs when they finally slip their shoes and socks off at the end of the day. This edema, which results from pooling of tissue fluid in dependent body parts, usually disappears following a short walk or elevation of the legs. When you’re forced to sit for prolonged periods, periodically standing and walking – or intermittently performing some toe raises if you can’t leave your seat – will help prevent this type of edema from developing in the first place.
While the pedal edema associated with pregnancy or prolonged sitting is usually self-limiting, persistent or recurrent foot swelling warrants a visit to a healthcare provider, as it could signal a serious underlying condition. In medical disorders where pedal edema occurs, diuretics (“water pills”) are routinely prescribed. Removal of excess fluid from the circulation not only alleviates the edema; it usually improves other symptoms associated with the underlying problem, as well. And, since excess sodium in the bloodstream and tissues encourages fluid retention, patients suffering from “fluid overload” are typically advised to restrict their salt intake.
For example, congestive heart failure, which is characterized by a reduction in the heart’s ability to push blood through the body, is frequently accompanied by pedal edema. When the blood returning to a weak heart has to “wait in line” before being pumped back out to the body, it gets temporarily stored in places where the hydrostatic pressures are lowest or the blood vessels are leakiest: the feet and lungs, usually. Excess tissue fluid in these body parts causes pedal edema and – as the air sacs in the lungs fill with fluid – shortness of breath. Removal of excess fluid with diuretics not only reduces pedal edema in patients with congestive heart failure; it often improves their breathing. And, because congestive heart failure paradoxically increases sodium retention, salt restriction is also a part of the therapeutic regimen for patients with this condition.
Other causes of bilateral pedal edema (swelling in both feet) include liver failure, kidney disease, venous insufficiency (often heralded by varicose veins) and certain medications (nonsteroidal anti-inflammatory drugs, calcium channel blockers and corticosteroids, for example). Diuretics may be indicated for these disorders, just as they are for congestive heart failure.
Unilateral pedal edema – swelling that occurs in only one foot or leg – is often caused by blockage of the venous return in the involved extremity. Venous insufficiency – typically a benign but chronic problem – can cause unilateral pedal edema that comes and goes. Sudden onset of unilateral foot or leg swelling could be caused by a blood clot in the veins of the leg. This condition, called deep vein thrombosis (DVT), can be life-threatening; immediate medical evaluation is warranted.
Diuretics are not indicated for treating venous insufficiency or DVT. Compression hose, weight control, avoidance of prolonged standing or sitting and daily walks are usually helpful for people with venous insufficiency; surgery may be indicated for severe cases. For patients with DVT, anticoagulants (“blood thinners”) are used to prevent the clot from extending up the leg or fragmenting to the lungs; hospitalization may be recommended when DVT is associated with signs or symptoms of clot fragmentation, such as shortness of breath, anxiety, rapid heartbeat or low blood pressure.
People who take prescription diuretics for pedal edema often question whether they can use herbal diuretics instead. Advocates of herbal diuretics argue – justifiably – that these preparations contain vitamins, minerals and other nutrients that aren’t found in prescription drugs. Unfortunately, herbal diuretics may not be potent enough to remove the volumes of fluid needed to successfully treat serious medical disorders, such as heart failure or end-stage liver disease. Therefore, while an herbal diuretic such as dandelion, horsetail, parsley or juniper might be useful for benign, self-limiting edema, people with medical conditions should always check with their physicians before supplanting their prescription diuretics with herbal ones. Pregnant women, too, should consult their midwife or doctor before using any herbal diuretic. While many herbal diuretics, such as dandelion or parsley, are generally considered safe when consumed as foods during pregnancy, not enough is known about these agents to ensure their safety at the higher dosages needed to increase urine flow. And some herbal diuretics, such as juniper, have been linked to miscarriages, premature labor or fetal damage.