It is well known that around 60% of human body is composed of water. The balance of water entering the body and being lost has to be carefully maintained as either extreme, both too much and too little water, can be dangerous. Excess water within the body is expelled mainly through the urine but also through the stool, breath as water vapor and via the skin as sweat (perspiration). Sometimes the body retains fluid and this can cause a host of problems.
What is fluid retention?
Fluid retention simply means that the body is retaining more water than it should. As a result the excess fluid may accumulate in the tissue spaces and body cavities resulting in various symptoms. It can also be retained within cells which may cause these cells to swell and even burst, or within the circulatory system thereby increasing total blood volume leading to disturbances like high blood pressure.
The medical term for fluid retention is edema. Sometimes the accumulation of fluid is restricted or more pronounced in one area and then referred to by various other terms. For example, fluid accumulation in the abdomen is known as ascites while fluid in the lungs is referred to as pulmonary edema. Anasarca is the medical term for generalized edema or swelling throughout the body.
Read more on abdominal swelling.
What happens with fluid retention?
The body has the ability to retain more water than is considered to be within normal limits without any significant symptoms. However, once this limit is greatly exceeded especially for long periods of time then it can cause a host of disturbances.
Fluid in the body is either within cells (intracellular fluid) or outside cells (extracellular fluid). The latter includes fluid in the circulatory system (heart and blood vessels), tissue spaces (between the cells) and cavities. The fluid can shift between compartments to ensure an optimal balance.
The main organ to regulate the fluid balance in the body is the kidney. It achieves this in conjunction with various hormones and electrolytes to either increase or decrease fluid excretion in the form of urine. However, fluid retention is not always linked to excess fluid in the body.
In some cases, fluid from one compartment like within the blood in circulation, seeps into another compartment. This occurs when blood vessels are malfunctioning and becomes leaky. Sometimes drainage of fluid around the cells is impaired due to dysfunctional blood or lymphatic vessels resulting in accumulation of fluid in a certain area.
Causes of Fluid Retention
Some of the possible causes of fluid retention has been discussed below. It is important to differentiate fluid retention from other reasons for distension, like fat accumulation and gas bloating.
Dietary causes of water retention varies from excess salt intake to nutritional deficiencies. With regards to salts, it can also the osmotic concentration which may shift the water balance by drawing fluids from one compartment to another. Fluid retention is also seen as a symptom of deficiencies of certain B-vitamins, especially vitamin B1 (thiamine), B5 and B6. It is also seen in malnutrition where there is a protein deficiency like kwashiokor.
The main lifestyle factor that can contribute to fluid retention is being sedentary. Muscles around veins play a role in moving blood back to the heart. When physically inactive, these muscles are not able to assist circulation as it normally should. As a result blood may pool in certain areas, particularly the periphery like the legs, eventually causing fluid to seep out of the blood vessel and into the tissue spaces.
Swelling is also seen with trauma, particularly with burns and following surgery. The fluid retention in these cases may be temporary until the tissue heals, heart activity returns to normal and a person is once again physically active. However, in severe cases like extensive burns the fluid retention can be life-threatening.
Inflammation is the body’s mechanism to protect against tissue damage. One of the consequences of this mechanism is a change in the permeability of blood vessels in the affected area. In other words the blood vessels become leaky. Fluid seeps out of the blood vessels and into tissue spaces resulting in swelling. Inflammation may occur for various reasons such as trauma, infections, allergies and autoimmune diseases.
Swelling may be seen with various types of cancers. Kidney cancer that may significantly affect kidney function can lead to fluid retention as a result of the disruption. Liver cancer may also have a similar effect. Some types of cancers may produce hormones which be the cause of fluid retention.
Certain organs play a central role in ensuring that the fluid balance is maintained throughout the body. Therefore diseases of these organs, and especially failure of these organs, can result in fluid retention. It is mainly seen with kidney, liver and heart failure which may occur for various reasons. Dysfunction of the thyroid may also play a role in swelling as is seen with myxedema which arises in hypothyroidism (underactive thyroid gland).
Hormones like vasopressin (also known as antidiuretic hormone or ADH) are central to maintaining the fluid balance. Vasopressin aids with the retention of fluid therefore high levels of vasopressin will lead to excessive fluid retention. The changes in hormone levels with pregnancy may also be responsible for fluid retention although this is temporary. Another hormonal problem where swelling may occur is thyroid diseases.
A number of different drugs can cause fluid retention for various reasons. This includes:
- Female hormone drugs like the oral contraceptive pill and hormone replacement therapy (HRT).
- Certain blood pressure and diabetes drugs.
- Non-steroidal anti-inflammatory drugs (NSAIDs).
A blood clot in a vein can prevent the return of blood to the heart. As a result blood accumulates in one area and the congestion may eventually lead to fluid seeping out of the vein. A similar effect may be seen in conditions like varicose veins where the valves of the veins malfunction. Blood pools in the legs as a result and causes swelling of the lower legs and feet.
- Protein-losing enteropathy
- Lymphatic filariasis
- Traumatic head injury
- Chronic obstructive pulmonary disease (COPD)
- High altitudes