Diabetes mellitus and diabetes insipidus share some symptoms but stem from issues with different hormones. Diabetes mellitus relates to blood sugar regulation. Diabetes insipidus affects fluid balance and urine concentration.

Diabetes mellitus is a group of conditions that impair the body’s ability to process blood sugar, or glucose. The most common types of diabetes include type 1, type 2, and gestational diabetes. While the exact cause differs between the types, difficulty regulating blood sugar typically relates to issues with the pancreas and how the body uses or produces the hormone insulin.

Diabetes insipidus describes a condition that affects the body’s ability to maintain fluid balance. It occurs when the body is unable to produce a hormone called vasopressin, or when the kidneys do not respond to this hormone. This means the kidneys cannot prevent water excretion or properly concentrate urine.

This article outlines the differences between diabetes mellitus and diabetes insipidus, including causes, diagnosis, and treatments.

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Diabetes mellitus and diabetes insipidus are not related. The naming and some symptoms of the conditions may be similar, but they have very different causes and treatment options.

The naming of the conditions is confusing and refers to an old diagnostic method for differentiating between the two. The term diabetes derives from the ancient Greek word meaning to pass through. Both mellitus and insipidus are Latin terms for sweet and tasteless.

As both conditions share symptoms of increased thirst and frequent urination, physicians would use a urine sample to distinguish between them. They would dip a finger in the sample to test if the urine was sweet, suggesting diabetes mellitus, or tasteless, indicating diabetes insipidus.

Both conditions involve different organs and hormones. Diabetes mellitus may involve the pancreas and occurs due to issues with insulin. This hormone is responsible for regulating blood sugar levels. If the pancreas does not produce enough, or the body does not respond to it, a person’s blood sugar levels will rise. This causes excess glucose to spill into the urine, dragging extra water and resulting in more frequent urination.

Diabetes insipidus instead involves the kidneys and issues with vasopressin. This hormone is responsible for regulating the amount of water the body passes in urine. If the body does not produce enough, or the kidneys do not respond to it, the kidneys will excrete too much water. This causes a person to pass large volumes of dilute urine.

As such, treatments for each condition differ as they attempt to treat the underlying cause or provide medications to replenish levels of these hormones.

For either condition, a person may experience frequent urination, or polyuria, and increased thirst, or polydipsia.

Additionally, other symptoms of diabetes mellitus may include:

Other symptoms of diabetes insipidus can include:

Diabetes mellitus usually occurs due to difficulties with insulin. The pancreas is either unable to produce enough insulin or cells stop responding to the hormone. Insulin is responsible for regulating levels of sugar in the bloodstream. Without it, blood sugar levels become too high, which can result in serious health issues. The most common types of diabetes mellitus include:

  • Type 1 diabetes: This type is an autoimmune disease. This means a person’s immune system mistakenly attacks healthy tissue. In this case, the immune system damages the beta cells present in the pancreas, meaning it can no longer produce enough insulin.
  • Type 2 diabetes: This type occurs due to insulin resistance. This refers to when the body no longer responds to insulin correctly. The pancreas may attempt to produce more insulin to compensate but eventually is unable to keep up.
  • Gestational diabetes: A person experiences this type of diabetes during pregnancy. It also occurs due to insulin resistance. The placenta releases hormones that interfere with how well insulin can function, causing blood sugars to rise.

Typically, diabetes insipidus results from issues with vasopressin. Different factors may contribute to the development of diabetes insipidus, such as damage to parts of the endocrine system, namely the hypothalamus or pituitary gland, or damage to the kidneys. The specific cause of diabetes insipidus varies among the four types.

  • Central diabetes insipidus: This type occurs due to a reduction or absence of vasopressin. It can be primary central diabetes insipidus, which is present from birth, or secondary, which a person may acquire due to brain lesions resulting from head injuries, cancers, or brain surgery.
  • Nephrogenic diabetes insipidus: This type results from how the kidneys respond to vasopressin. It can occur due to kidney cysts, kidney infections, or certain medications.
  • Gestational diabetes insipidus: In some cases, pregnancy can affect vasopressin levels. This is typically due to the placenta releasing an enzyme that reduces vasopressin levels.
  • Dipsogenic diabetes insipidus: Issues with the hypothalamus can cause this type of diabetes insipidus. Issues can result from damage to the hypothalamus, mental health conditions, or certain medications.

As diabetes mellitus and diabetes insipidus may initially present with similar symptoms, they are often a differential diagnosis for each other. A doctor will first perform a physical examination, view medical history, and ask about symptoms. They will then typically request tests, such as urine and blood tests, to help differentiate the conditions.

For example, different types of blood tests can measure a person’s blood sugar levels to determine if they are high and indicate a diagnosis of diabetes mellitus. Additionally, a doctor can also perform genetic testing or look for the presence of autoantibodies in the blood to determine which type of diabetes mellitus a person has. A urine test cannot diagnose diabetes mellitus, but the presence of sugar in the urine can suggest it.

To diagnose diabetes insipidus, a doctor can test urine to check whether it is too watery and measure blood for high sodium levels. To confirm the diagnosis and determine which type of diabetes insipidus a person has, a doctor can perform further tests, such as imaging scans of the brain or testing how the body responds to vasopressin.

The main goal for both conditions is to restore either blood sugar or urine concentration to appropriate levels. A person can typically achieve both of these through a combination of medications and lifestyle behaviors.

For type 1 diabetes, treatment involves the administration of insulin to help keep blood sugars within target ranges. For type 2, a person may also use insulin or take other medications, such as metformin. In some cases, a doctor will also recommend insulin for gestational diabetes.

A doctor will also suggest certain lifestyle behaviors to help manage blood sugars for type 1, type 2, and gestational diabetes. These can include managing weight, a varied dietary pattern, and regular physical exercise.

For diabetes insipidus, treatment typically involves the administration of desmopressin. This is a synthetic version of vasopressin available in different forms, such as a tablet, injection, and nasal spray. For nephrogenic diabetes insipidus, a doctor will instead treat the underlying cause, which may include switching medications or prescribing a class of diuretics known as thiazides to help reduce the amount of urine the kidneys produce.

A doctor may also suggest reducing salt and protein intake to help the kidneys produce less urine.

Diabetes mellitus and diabetes insipidus are different and unrelated conditions. Diabetes mellitus typically relates to issues with insulin and regulating blood sugars, while diabetes insipidus occurs due to issues with vasopressin and urine concentration.

A doctor may be able to diagnose either condition from blood and urine tests. To help treat and manage both conditions, a doctor can prescribe medications and suggest lifestyle changes to help a person control their blood sugars and urine concentration.