Water retention, also known as fluid retention refers to an excessive build up of fluid in the circulatory system, body tissues, or cavities in the body.
Up to 70% of the human body consists of water - water exists both inside and outside our body's cells. Blood is mostly made up of water, as are our organs and muscles.
A complex system of hormones and prostaglandins (hormone-like substances) is used by the human body to regulate water levels. This means that excess water intake can be resolved by the kidneys quickly excreting the excess fluid in the form of urine. Likewise, reduced hydration on another day can result in a decreased urine output than usual.
Up to 70% of our body is water:
- Muscle is made up of approximately 75% water
- Fat consists of about 50% water
- Bones are made up of about 50% water.
Causes of water retention
Water retention can occur in many different areas of the body and for differing reasons. We will look at these individually.
Fluid (liquid) rich in nutrients, vitamins and oxygen continuously passes from tiny blood vessels (capillaries) into surrounding tissues - this fluid is known as interstitial fluid (tissue fluid). Interstitial fluid nourishes cells and eventually makes its way back to the capillaries.
Water retention may occur if pressure inside the capillaries changes. Water (fluid) retention is also possible if something occurs that makes the capillary walls too leaky. If something goes wrong with capillary pressure or capillary wall permeability (wall becomes too leaky), excess liquid (fluid) will be released into the tissue spaces between cells. If too much fluid is released more and more of it will remain in the tissues, rather than returning to the capillaries, resulting in swelling and water logging (water retention).
The lymphatic system
The lymphatic system, which consists of a network of vessels throughout the body, drains lymph (a fluid) from tissues and empties it back into the bloodstream. However, if too much fluid is released in the first place the lymphatic system can be overwhelmed - it is unable to return fluid fast enough, and it accumulates around the tissues (fluid retention).
Sometimes, if the lymphatic system is congested, there may be something wrong with the rate at which fluid is returned back into the bloodstream. This means that fluid can remain in the tissues, causing swelling in various parts of the body, including the abdomen (ascites) or ankles, legs and feet (edema).
The lymphatic system is a network of vessels that carry a clear fluid called lymph.
Normal pressure within blood vessels is partly maintained by the pumping force of the heart. However, if the heart starts to fail (congestive heart failure), there will be a change in blood pressure, which often results in serious water retention.
Typically, the legs, feet and/or ankles will swell. Fluid will also build up in the lungs, giving the patient a chronic (long-term) cough.
Congestive heart failure can eventually cause breathing problems, as well as excessive stress on the heart. The patient will probably be prescribed diuretics. A diuretic is anything that promotes the formation of urine by the kidney - in other words, anything which helps the body shed water.
A diagram of the kidneys.
Our kidneys carry out the complex system of filtration in our bodies - excess waste and fluid material are removed from the blood and excreted from the body. Our kidneys get their blood and oxygen supply from the renal arteries, which are branches of the abdominal aorta (another artery). When it enters the kidneys, blood goes through smaller and smaller blood vessels - the smallest ones being the glomeruli (tiny capillary blood vessels which are arranged in tufts).
It is in the glomeruli that blood is filtered - waste, fluids and other substances are extracted and cross into miniscule tubules, from which the bloodstream reabsorbs what the body is able to reuse. What the body cannot reuse - waste - is excreted in our urine.
In most cases our kidneys are able to eliminate all waste materials that our body produces. However, if the blood flow to the kidneys is affected, or the tubules or glomeruli are not working properly because of damage or disease, or if urine outflow is obstructed, problems can occur. Including kidney failure - then waste material, including fluids, cannot be eliminated (shed) from the body properly, resulting in fluid retention.
The weight of the uterus on the major veins of the pelvis can cause a buildup of fluid in the body during pregnancy. In most cases it is nothing to worry about and generally resolves after the baby is born.
Physical activity (exercise) helps the leg veins return blood to the heart (against gravity). If the blood does not travel fast enough it will begin to accumulate in the legs, resulting in higher pressure in the capillaries. Fluid will leave the capillaries at a higher rate because of the higher pressure. The higher pressure also makes it harder for fluids to come back later on. Eventually, some capillaries may break; leaving small blood marks under the skin, and the veins can become swollen and distorted (varicose veins).
Long haul flights can increase your risk of water retention.
Exercise is also needed to stimulate the lymphatic system to fulfill its function of regulating overflow - bringing fluids back into the bloodstream at rates which may regulate body water levels. Very long periods of physical inactivity, such as a long-haul flight, increase the risk of water retention. During a long-haul flight, even minor physical movements, such as standing on tiptoes and down a few times, rotating the ankles and wiggling the toes can help reduce fluid retention.
Humans require a certain level of proteins for effective water balance. An individual with severe protein deficiency may find it harder to get the water from the tissue spaces back into the capillaries. The enlarged abdomens of seriously malnourished and/or starving people are mainly caused by a lack of protein in their diet.
When an inflammation is present in the body, histamine is released. Histamine causes the gaps between the cells of the capillary walls to widen, making them more leaky. The aim is to make it easier for infection-fighting white cells to quickly get to the site of an inflammation (infection). However, if the inflammation persists for a long time, water retention can become chronic (long-term).
Some medications can cause water retention, including:
- Estrogen-containing drugs, such as the combined oral contraceptive pill, or HRT (hormone replacement therapy).
- NSAIDs (non-steroidal anti-inflammatory drugs) - medications with analgesic (pain reducing), antipyretic (fever reducing) effects. In high doses they are actually effective in reducing inflammation. Examples include aspirin, ibuprofen and naproxen.
- Beta-blockers - used to treat abnormal heart rhythms and prevent tachycardias.
Pre-menstrual water retention
This causes bloating and can cause breast tenderness. Experts say it is due to hormone imbalances, and also some nutritional factors. Premenstrual refers to the second half of the woman's menstrual cycle (during the days or the week or so before her period begins).
Sodium-rich foods may cause water retention.
Malnutrition and/or bad diet
Dieticians say low consumption of thiamine (vitamin B1), as well as insufficient vitamins B6 and B5 may contribute toward fluid retention. Low levels of albumin levels may also play a part - low albumin levels can also be caused by kidney disease.
Some foods and insect bites may cause edema in susceptible people.
People with a disorder of the thyroid gland can commonly experience water retention.
On the next page we look at treatments for water retention and some self-help prevention tips.