Polydipsia Vs Dehydration

Introduction

Polydipsia and dehydration are both related to fluid regulation. Dehydration occurs when the body loses more fluids than it takes in and can be lost through excess sweating, vomiting, diarrhoea and inadequate fluid intake.¹ This may cause symptoms such as a dry mouth and thirstiness, which would encourage drinking water, to alleviate these symptoms.¹

On the other hand, polydipsia is a feeling of excessive thirst and an abnormal urge to drink large volumes of fluids. Polydipsia can last from weeks to months at a time.² This feeling of excessive thirst cannot be quenched by drinking fluids and is usually due to an underlying condition such as diabetes.

So whilst dehydration and polydipsia are linked, in the sense that thirst is triggered by dehydration and polydipsia is a form of excessive thirst, they represent different aspects of fluid regulation and have various causes and health risks.³ This article will discuss how dehydration and polydipsia differ, their treatment strategies and the best ways to avoid these complications.

The importance of understanding the differences between polydipsia and dehydration

It is important to understand the differences between these two processes, as there are distinct ways to manage and treat them. Dehydration is treated with the aim of restoring hydration whilst treating polydipsia would involve addressing underlying health conditions.

Failing to distinguish between the two, could have serious health implications. Administering fluids to an individual who has polydipsia could exacerbate the problem causing serious fluid overload, while not recognising dehydration promptly could lead to dangerous long-term effects.^1,4

Polydipsia: definition and causes

Polydipsia is the medical term for excessive thirst and/or excessive drinking. There are two types of polydipsia: primary and secondary. In clinical practice, secondary polydipsia is where excessive thirst is prompted by an actual need for water and is caused by an underlying medical condition or medication.²

In contrast, primary polydipsia involves the excess consumption of fluids without underlying dehydration. This means that the individual is just drinking in excess, rather than drinking fluids to correct a fluid imbalance. Individuals may drink fluids in excess as they believe it has health benefits, this is referred to as dipsogenic polydipsia, or because they have a psychiatric disorder.

Although rare, some people will consume excessive quantities of liquids due to psychological disorders such as schizophrenia or obsessive-compulsive disorder, this is known as psychogenic polydipsia.⁴

Health concerns

Polydipsia is a common symptom of diabetes mellitus. Diabetes is characterised by high blood sugar levels, also known as hyperglycemia. The excess glucose in the bloodstream cannot be absorbed by the cells and therefore, the body tries to dilute the glucose by drawing water from cells into the bloodstream.

This in turn leads to polyuria, which is a medical term used to describe the increased need to urinate.⁵ This loss of water consequently leads to excessive thirst. If a doctor suspects diabetes mellitus is the cause of polydipsia, urine samples will be taken, and blood tests measuring glucose levels will also be collected. 

• FPG test (Fasting Plasma Glucose test): Glucose levels will be measured after 8 hours of fasting, levels that are above 126 mg/ml indicate diabetes
• ORG test (Oral Glucose Tolerance test): Patients are given an oral glucose solution to drink and after two hours, blood glucose levels are measured. Levels above 200 mg/dl indicate diabetes
• Urinalysis: tests for the presence of glucose in the urine (glycosuria). This is a typical sign of diabetes

Polydipsia is a common symptom for people with diabetes mellitus but many other medical conditions can cause polydipsia: 

• Kidney diseases or damage to the kidney can affect the body's ability to regulate fluids and electrolytes. An imbalance of electrolytes can trigger long-term t thirst as the body tries to restore equilibrium. For example, diabetes insipidus, which is caused by dysregulation of the hormone vasopressin leads to kidney dysfunction
• Hypokalemia (low potassium levels) an essential electrolyte, disrupts fluid balance at low levels. This can be caused by gastrointestinal, endocrine and eating disorders
• Medications, such as diuretics, which are used to treat high blood pressure that work by increasing urine production, antidepressants, ACE inhibitors used to treat heart and kidney problems, and anticholinergics used to treat parkinsons and IBS can all cause polydipsia as a side effect^2,4

It must be noted that while dehydration triggers initial thirst polydipsia persists beyond the immediate need to replace fluids. Long-term periods of excessive thirst as mentioned in the examples above may not be directly related to fluid balance but other issues such as medication or hormonal imbalances.

Symptoms of polydipsia 

The difference between normal thirst and polydipsia is quite significant. 

Polydipsia is a constant thirst irrespective of the volume of fluid consumed. Everybody gets thirsty from time to time but in polydipsia, the feeling of thirst lasts for long periods - sometimes even weeks and months despite consuming large volumes of water.

Symptoms are a dry mouth, a feeling/need to drink large amounts of fluids and also frequent urination. Other symptoms may vary depending on the underlying health conditions associated with the polydipsia.

Examples include:

• Weight changes
• Fatigue and weakness
• Seizures 
• Heart problems 
• Confusion
• Tremors 
• Nausea/Vomiting^2,4

Diagnosis and treatment

Treatment for polydipsia depends on the underlying medical condition causing the excessive thirst, because of this a comprehensive evaluation will be completed by a doctor.² Medical history and medications taken will be examined to determine what may be causing the problem. Urine samples and glucose blood tests can then be taken depending on what the doctor suspects is the cause.

For an individual with diabetes mellitus this may be lifestyle changes, for someone with primary polydipsia this could be behavioural therapy. In most cases and especially chronic conditions such as kidney diseases causing polydipsia, the patient must be regularly monitoring their fluid intake and other symptoms to reduce any further complications.²

Doctors may also assess kidney function and ask if there are other associated symptoms beyond the feeling of thirst to understand the cause better.

Dehydration

Dehydration is when the body loses more fluids than is being taken in. When water levels are low, it disrupts the balance of salt and sugars in the body, affecting how it functions.¹ A variety of factors can disrupt fluid intake or increase fluid output such as:

• Insufficient fluid intake
• Excessive fluid loss e.g vomiting, diarrhoea, sweating
• Diabetes 
• Heatstroke 
• Excessive alcohol consumption
• Diuretic medication
• Fever¹

Younger and older Individuals, as well as those with chronic illness, are more susceptible to dehydration as they may have decreased thirst sensation, limited mobility and a decline in physical and cognitive function. This may mean they are less aware of their need to hydrate and are unable to communicate effectively with someone who can provide water. However, for the majority of the population dehydration is easy to spot.

Symptoms

There are a variety of symptoms that are associated with dehydration that range from mild to severe.¹ Some of them include:

• Feeling thirsty
• Dry Mouth 
• Tiredness 
• Disorientation
• Dry lips
• Dark and strong-smelling urine
• Headaches 
• Muscle cramps
• Potential heart arrhythmias 
• Constipation 
• Heatstroke

Dehydrated babies may have the following symptoms:

• A sunken soft spot on their head - known as the fontanelle 
• They may sleep more than usual
• Have fewer wet nappies
• Have fewer tears why crying

Diagnosis and treatment

Recognising dehydration tends to be easier in the general population. For mild cases of dehydration, an oral rehydration solution with electrolytes is usually sufficient to restore fluids. Rehydration packets are available over the counter at pharmacies and can be recommended after fluid loss from vomiting, diarrhoea or excessive sweating.

For more severe cases of dehydration hospitalisation, and intravenous fluid administration may be required. Fluids and electrolytes are delivered directly to the bloodstream to rapidly hydrate the individual. IV administration may also be required for individuals who are unable to tolerate oral fluids due to vomiting or gastrointestinal illness.

After hydration levels are restored it's important to address the underlying cause of the loss of fluids and implement a plan to prevent future occurrences. While mild dehydration is common and easily reversible, severe dehydration can result in seizures and even death, so it is important to take the necessary steps to maintain hydration.¹

FAQs

When to seek medical attention for dehydration?

The NHS recommends calling 111 for help and advice if feeling unusually tired, disoriented and dizziness that doesn’t go away after standing up and drinking. Promptly seek medical advice if you are concerned about a child or infant that is dehydrated.¹

When to seek medical attention for polydipsia?

After prolonged unexplained periods of excessive thirst, It is important to note if you already have any underlying medical conditions associated with polydipsia that fluid levels and urination should be closely monitored.²

What are some top tips to maintain hydration?

Try to ensure your urine is a pale colour throughout the day. If you anticipate there is a higher chance of dehydration due to the weather, exercise or illness, drink more throughout the day and try to drink regularly.

Can polydipsia be prevented?

Preventing polydipsia involves addressing the underlying conditions that contribute to excessive thirst.

Is polydipsia a disease?

No. Polydipsia is a symptom of other conditions such as diabetes.

Summary

To summarise dehydration is the state of being in a fluid deficit, while polydipsia involves the feeling of excessive thirst that isn’t quenched after consuming large amounts of water. Both involve fluid regulation however the underlying mechanisms causing dehydration and polydipsia can be very different.

Polydipsia usually stems from underlying medical conditions and can persist over long periods while dehydration can vary in terms of severity and may occur acutely or chronically. It is important to recognise and distinguish between them both as how they are addressed and treated is different and both can lead to serious complications