WATER constitutes 60 percent of the body weight and it is widely known that humans cannot survive without water for long. Reduced water intake may lead to dehydration while excessive consumption may result in water intoxication.
Salt (sodium chloride) is a very essential constituent of the body and it is found in most of foods. Sodium has an important role in the regulation of blood pressure and blood volume. It is the most abundant element in the body fluids.
Low sodium level in the blood is called hyponatremia, a condition characterised by abnormal brain functions. Excess salt intake may worsen blood pressure, precipitate cardiac failure and trigger kidney diseases.
There are many misconceptions regarding the recommended intake of salt and water. It is important that the body is adequately hydrated. Good urine output, absence of significant thirst and healthy skin are markers of adequate hydration. People who are exposed to hot weather conditions and those involved in strenuous activities lose water as sweat.
Though the thirst mechanism is sufficient to take care of the water needs, it is essential to drink plenty of water so that good urine output is maintained.
Patients with kidney stones should also drink plenty of water to prevent crystallisation of various salts like calcium oxalate in the urine.
It is important that they pass at least 2500 ml of urine every day. They should also make sure that water intake is distributed throughout the day.
A healthy average sized adult can consume up to 12-14 litres of water a day.
The kidneys will not be able manage water intake beyond this limit and it may lead to ‘water intoxication’. This is a condition characterised by low sodium level, convulsions and loss of consciousness which can be life threatening.
There are some psychiatric conditions like a craving for water intake exceeding this limit. Although the body can handle up to 12-14 litres of water a day, the kidneys can produce only up to 800 ml of urine per hour. Hence if a large quantity of water is consumed over a short span of time, it can result in water intoxication.
This phenomenon may occur in patients awaiting radiology procedures who are instructed to drink plenty of water to ensure that the urinary bladder is full.
With declining kidney and cardiac functions, the ability to handle water load comes down. Creatinine level in the blood is the parameter often used for measuring kidney functions. In a healthy adult, creatinine level will be less than 1.4 mg/ dl.
Though severe kidney failure is associated with high creatinine level, any value higher than 2 mg/dl suggests impaired kidney functions. A significant number of chronic diabetes and hypertension pat ients have mi ld t o moderately der a n g e d k i d n e y functions.
T h o u g h they are oedema free and are able to tolerate the usual water load, excess water intake is likely to cause hyponatremia.
Patients with heart failure should also restrict water intake as excess fluid may worsen this condition.
That increased water intake will improve kidney functions is a myth.
Salt has an important correlation with blood pressure. Though all mammals share a similar physiology, hypertension, which is uncommon in animals and common in humans, is linked to the increased salt intake among humans.
Although in a healthy individual extra salt load can be handled by the kidneys, prolonged high consumption of salt may lead to hypertension, cardiovascular diseases and renal diseases.
Healthy individuals should also restrict salt intake to less than 8 gram per day.
Increased salt consumption can worsen fluid overload and heart failure.
Those with hypertension should reduce the intake to 4 g per day and those who require drugs to control blood pressure and have swelling of the body, or kidney/ heart failure should restrict the intake even further.
The intake of pickles, papad and preserved foods rich in salt should be restricted.
Hypertension is becoming common. One of the reasons cited is the increased consumption of rich foods with high salt content.
While adequate water intake to prevent dehydration is important, drinking water in excess quantities has no known scientific benefits.
People with compromised kidney and heart functions should restrict fluid intake to prevent fluid overload and hyponatremia.
Patients with hypertension and disorders of the kidney and heart should also restrict salt intake. But do not avoid salt altogether.
Dr Abi Abraham M
Senior Consultant Nephrologist Lakeshore Hospital Email: dr.abiabraham@gmail.com
