Diabetes Insipidus vs Mellitus: What’s The Difference?

If you hear the term diabetes, you most likely think of the disease that affects your blood sugar levels. 

This is the most common type of diabetes, but there is another health condition that shares part of the name – diabetes insipidus.

Diabetes insipidus and diabetes mellitus get their names from Latin root words and reference back to when health practitioners had to taste patients’ urine to determine their diagnosis. 

They didn’t have urinalysis or blood tests back then!

Diabetes mellitus refers to honey-tasting or sweet urine due to high levels of glucose (sugar) in it. 

Diabetes insipidus refers to “tasteless” urine, usually clear in color, which is produced in excessive amounts and doesn’t contain glucose.

While they both have to do with urine, these two health conditions are quite different. Keep reading for a complete comparison of diabetes insipidus vs mellitus.

What is diabetes insipidus?

Diabetes insipidus (DI) is a rare disorder that causes an imbalance of fluids and electrolytes in your body. Diabetes insipidus causes your body to make large amounts of urine, which can lead to dehydration, low blood pressure, and other issues (1). 

Someone with diabetes insipidus can make up to 20 quarts of urine per day, when the more typical amount is around 1-3 quarts per day.

Diabetes insipidus is quite rare, impacting around 3 in 100,000 people. It’s typically caused by a brain tumor impacting the pituitary gland or hypothalamus or from severe head trauma that damages these areas in your brain.

What is diabetes mellitus?

Diabetes mellitus (DM) is a group of chronic diseases that impact your body’s ability to metabolize glucose properly. Glucose, or blood sugar, is your body’s main fuel source and is essential for survival (2). 

There are two main types of diabetes: type 1 and type 2. Type 1 diabetes is often diagnosed in childhood and is an autoimmune disease that attacks the cells in your pancreas that produce insulin. Insulin is a hormone that helps glucose enter your cells from your bloodstream to provide them with fuel.

Diabetes is estimated to impact nearly 11% of the United States population. Of the people who have diabetes, the majority of them have type 2. 

Millions of people also have prediabetes, a condition that increases your risk of developing type 2 diabetes by as much as 50% within the next 5-10 years after diagnosis.

Symptoms of diabetes insipidus vs mellitus   

Some of the symptoms of diabetes insipidus and diabetes mellitus are similar, while others are more distinct. The main difference between the two lies in how much urine is produced. It will be much higher with diabetes insipidus than with diabetes mellitus.

Signs of diabetes insipidus

• Urinating large amounts of colorless urine, up to 20 quarts a day, compared to the more normal amount of 1-3 quarts per day
• Thirst
• Dry mouth
• Feeling dizzy or light-headed when standing due to low blood pressure & dehydration
• Feeling tired
• Difficulty performing simple mental tasks
• Nausea
• Fainting

Signs of diabetes mellitus

• Increased thirst
• Increased urination
• Losing weight without trying
• Presence of ketones in your urine
• Fatigue
• Feeling irritable or having other mood changes
• Blurred vision
• Poorly-healing wounds
• Increased infections (gum infections, skin infections, yeast infections, etc.)

Diabetes insipidus is more likely to occur more abruptly, such as after the diagnosis of a brain tumor or a traumatic brain injury. In contrast, diabetes mellitus has a much slower onset and can progress over several years. Diabetes mellitus often has no symptoms until it’s progressed, which is why it’s a dangerous and often silent disease.

Getting screened for diabetes mellitus can help reduce your risk of developing it. If you have prediabetes (a condition where your blood sugar levels are high but not high enough to be considered diabetes), you have a good chance of reversing it with healthy lifestyle changes.

Causes of diabetes insipidus vs mellitus    

Diabetes insipidus

If you have diabetes insipidus, your body doesn’t make enough antidiuretic hormone (ADH), also called vasopressin. 

ADH helps prevent dehydration by helping the kidneys retain fluid. If diabetes insipidus is caused by a lack of ADH, it’s called central diabetes insipidus.

The rarest form of diabetes insipidus is called nephrogenic diabetes insipidus and occurs when your kidneys don’t respond to ADH. This type can be genetic and prevents your body from reabsorbing water back into your bloodstream.

Diabetes insipidus can be caused by trauma to your pituitary gland or hypothalamus, whether by brain surgery, a brain tumor, or a traumatic head injury. These are the most common causes of diabetes insipidus.

Other things that can increase your risk of diabetes insipidus include a family history of diabetes insipidus, taking medications that can cause kidney issues, and metabolic disorders that cause altered blood levels of certain minerals.

Diabetes mellitus

Unlike type 1 diabetes, type 2 diabetes isn’t an autoimmune disease. Type 2 diabetes usually occurs in adulthood, but it can also impact adolescents. 

Type 2 diabetes occurs from insulin resistance, which is when your body doesn’t respond to insulin the way it should. Over time, insulin resistance can result in insulin deficiency, more similar to type 1 diabetes.

While the risk factors for type 1 diabetes aren’t as clear, the risk factors for type 2 diabetes are more well-established. 

Some of the biggest risk factors for developing type 2 diabetes include having prediabetes (borderline diabetes), being over the age of 45, having a family history of diabetes, being overweight or obese, and not being physically active.

Another type of diabetes is gestational diabetes, which occurs during pregnancy. Many women with gestational diabetes don’t have diabetes before pregnancy, and it usually doesn’t persist after the pregnancy is over.

Diagnosing diabetes insipidus vs mellitus    

Diabetes insipidus

Water deprivation test

During a water deprivation test, you will withhold fluids for several hours to assess how your body responds. 

Your urine output, weight, and levels of ADH hormone will be measured during a water deprivation test to see if your body is making enough ADH. 

Magnetic resonance imaging (MRI)

An MRI can detect issues with your pituitary gland or hypothalamus, which might indicate diabetes insipidus. This test is especially useful if you have a history of head trauma or a brain tumor, which can cause diabetes insipidus in a previously otherwise healthy person.

Urine tests

A urine test can determine how concentrated your urine is. This can be helpful when diagnosing diabetes insipidus.

Genetic screening

Some types of diabetes insipidus are genetic. Genetic testing can determine if you’ve inherited diabetes insipidus.

Diabetes mellitus

Diabetes is diagnosed with blood sugar tests such as fasting blood sugar, random blood sugar, and a hemoglobin A1c test. These tests are usually done in a laboratory setting and most often use a venous blood draw versus a fingerstick test.

• Hemoglobin A1c: A hemoglobin A1c of 6.5% and above indicates diabetes. The hemoglobin A1c test measures your average blood sugar levels over the past 2-3 months and helps diagnose diabetes and prediabetes.
• Fasting blood sugar: Fasting blood glucose of 126 mg/dL or higher is indicative of diabetes.
• Random blood sugar: Any random blood sugar of 200 mg/dL or higher is usually indicative of diabetes.

For gestational diabetes, you’ll likely have a glucose tolerance test where you drink a sugary drink and have your blood sugar level measured one, two, and three hours afterward.

You’ll usually be screened for gestational diabetes between 24-28 weeks of gestation. If you don’t pass the initial screening, you’ll likely be referred to do the three-hour glucose tolerance test. If you fail the three-hour glucose test, you’ll most likely receive a diagnosis of gestational diabetes and be advised on a treatment plan.

Treatment for diabetes insipidus vs mellitus    

Diabetes insipidus

Low-sodium diet

This can help prevent fluid retention, which can further cause electrolyte imbalances. You might also be encouraged to eat a lower-protein diet which helps your kidneys not produce as much urine. 

A lower-sodium diet can also reduce thirst, which is often prevalent with diabetes insipidus due to the high volume of urine loss.

IV fluids/electrolyte replacement

If you have dehydration from increased urination, you might need to be treated with IV fluids to restore fluid balance. 

If you have low blood levels of certain minerals like potassium from a fluid imbalance or diuretic use, those can be replaced in a hospital setting using IV fluids.

Antidiuretic drugs 

Antidiuretic drugs like Desmopressin help your body not produce as much urine. Desmopressin is a synthetic version of vasopressin (ADH), the hormone often lacking if you have diabetes insipidus. Antidiuretic drugs help reduce thirst and reduce dehydration by helping your body hold on to more fluids.

Diuretic drugs

It might seem counterintuitive to use a diuretic to treat increased urination since most diuretics cause increased urination. While paradoxical, drugs like thiazide diuretics are used to treat diabetes insipidus by helping reduce the rate at which your kidneys filter blood, which reduces the amount of urine produced.
Your electrolyte levels will likely be monitored to prevent imbalances that can occur from diuretic use, such as low potassium (hypokalemia).

Non-steroidal anti-inflammatory drugs (NSAIDs)

These types of medications are often used along with thiazide diuretics to help reduce the amount of urine produced. Taking NSAIDs over a long period can increase your risk of stomach ulcers, so you should only take medications as prescribed and recommended by your healthcare provider.

Diabetes mellitus

Diet changes

Carbohydrates are a type of nutrient that turns into blood glucose and are found in foods like grains, fruit, some dairy products like milk and yogurt, legumes, and foods with added sugar. 

Eating a healthy diet low in added sugars and moderate in carbohydrates can help treat diabetes mellitus.

Some people can manage their diabetes with diet and lifestyle alone, while others need medication. Needing medication isn’t necessarily an indicator of an unhealthy lifestyle or “non-compliance” by the patient – some patients develop insulin deficiency and don’t make enough insulin over time, which can require medication.

Physical activity

Being physically active helps improve blood sugar levels and insulin sensitivity. It’s recommended to engage in at least 30 minutes of physical activity most days of the week to help manage blood sugar levels. Both cardiovascular exercise and resistance/weight training are beneficial.

Medications

Several types of medications are used to treat diabetes, including insulin, sulfonylureas, metformin, and non-insulin injectable medications. Metformin is a common first-line drug therapy for people with type 2 diabetes. 

People with type 1 diabetes are only treated with insulin, which can be a combination of long-acting, short-acting, and intermediate-acting to achieve blood sugar goals.

At-home blood sugar monitoring

Your healthcare provider might recommend checking your blood sugar levels at home using a glucometer. 

Testing your blood sugar levels at home gives you more insight into what impacts your blood sugar levels and whether or not your current treatment plan is effective. It can also help identify low blood sugar, which can cause dizziness and fainting if left untreated.

Similarities and differences between diabetes insipidus vs mellitus    

Similarities

• Both can cause increased urine production, increased thirst, fatigue, and dehydration.
• They both involve altered hormone response (insulin/DM, ADH/DI) – because they are related to hormones. An endocrinologist can help treat both conditions.
• Both can involve the use of medications for treatment.

Differences

• Diabetes mellitus causes high blood sugar, while diabetes insipidus doesn’t
• There are lifestyle factors that increase your risk of diabetes mellitus, whereas risk factors for diabetes insipidus aren’t lifestyle-related
• Diabetes insipidus is very rare, while diabetes mellitus is common
• Diabetes insipidus can’t be managed through lifestyle changes and requires medication and other treatments to prevent dehydration.

Can you have diabetes insipidus and diabetes mellitus at the same time?

While it’s technically possible to have both diabetes insipidus and diabetes mellitus at the same time, it would be extremely rare and very unlikely. While around 1 in 10 people have diabetes, only 1 in 25,000 of the general population will have diabetes insipidus.

Conclusion

While diabetes mellitus (DM) and diabetes insipidus (DI) have similar names, that’s where most of their similarities end. Both conditions have to do with urine output (that’s how they’re named), but the causes and treatment of both are quite different.

Some key differences to note:

• Diabetes mellitus occurs from high blood glucose levels, while diabetes insipidus is caused by a hormonal imbalance, most often due to head trauma, brain tumors, or brain surgery, resulting in a fluid imbalance due to excessive urine output.
• Diabetes mellitus is relatively common, while diabetes insipidus is quite rare.
• The main distinguishing characteristics between DM and DI are: blood sugar levels are high with DM, not DI; urine output is very high with DI, and not nearly as high with DM.

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