Read more on post.

Diabetes mellitus – known to many as type 1 and type 2 diabetes – gets all the attention with its rising global prevalence and connection to lifestyle and autoimmunity. Meanwhile, its lesser-known relative – diabetes insipidus – more quietly affects hundreds of thousands of people worldwide, but is an altogether different condition, unrelated to blood sugar.

Both forms share the same defining symptom: excessive urination. The word diabetes comes from ancient Greek meaning “passing through”, which perfectly captures what happens to newly affected patients.

In the more-familiar diabetes mellitus, sugar builds up in the blood because the body either doesn’t make enough insulin or can’t use it properly. When this happens, extra sugar enters the urine, and that sugar pulls water out of the body along with it.

People with diabetes may notice that they need to urinate more often and in larger amounts than usual. Sometimes, the urine can even have a sweet smell. Legend has it that Hippocrates, the “father of medicine”, used to taste his patients’ urine to make the diagnosis. Thankfully, we now use dipstick tests instead.

Diabetes insipidus is very different from diabetes mellitus. It has nothing to do with blood sugar. Instead, the problem is with a hormone called arginine vasopressin (AVP), also known as anti-diuretic hormone (ADH), which normally helps the body control how much water it keeps or loses.

This chemical messenger, produced by the pituitary gland at the base of your skull, acts like your body’s water conservation system. When you need to hold on to fluid – say, when you’re dehydrated – AVP tells your kidneys to reabsorb water rather than letting it escape in urine.

When this system breaks down, the results are dramatic. Without enough AVP, or when the hormone fails to function properly, your kidneys lose their ability to conserve water. No matter how much you drink, you remain perpetually thirsty and dehydrated, producing large volumes of pale, diluted urine. It’s a frustrating cycle that affects around 2,000 to 3,000 people in the UK alone.

The most common culprit is AVP-deficiency (formerly called central diabetes insipidus), where the problem lies in AVP production itself. It’s actually made in a brain region called the hypothalamus before being transported to the pituitary gland, from where it is released.

Brain tumours can damage this delicate system, as can head injuries or brain surgery. Genetics sometimes plays a role, and neurological infections like syphilis or tuberculosis can also disrupt hormone production. In some cases, however, doctors are unable to identify a clear cause.

Pregnancy brings its own unique version called gestational diabetes insipidus. The growing placenta produces an enzyme that breaks down AVP in the bloodstream before it can do its job. Fortunately, this rare condition typically resolves after birth.

For AVP-deficiency, treatment is more straightforward. Patients can take desmopressin, a synthetic version of AVP available as tablets, injections, or even a nasal spray. This replacement therapy effectively restores the body’s ability to conserve water.

Things get trickier with AVP-resistance (formerly called nephrogenic diabetes insipidus), where the kidneys themselves fail to respond to AVP.

Sometimes present from birth, this form can also develop later due to kidney damage from electrolyte imbalances or certain medications. Lithium, commonly used to treat bipolar disorder, is one such example. Since the problem is the kidneys’ inability to respond to AVP, different medications are used. Low-salt diets and careful attention to staying hydrated are also key.

When thirst goes wrong

Perhaps most puzzling is dipsogenic diabetes insipidus, where the brain’s thirst centre goes haywire.

Also located in the hypothalamus, this control centre can be damaged by tumours, trauma, or infections, leading to an insatiable urge to drink water. The excessive fluid intake then suppresses AVP production, creating a vicious cycle. Dangerously, it can dilute blood sodium levels, causing headaches, confusion and even seizures.

The symptoms of this condition sometimes overlap with psychogenic polydipsia, where mental health disorders – particularly schizophrenia – drive compulsive water drinking. The consequences can be severe, as seen in one documented case where a young patient suffered complications after consuming an astounding 15 litres of water per day.

These extreme examples of pathological water intake stand alongside wellness trends promoting excessive hydration as part of a healthy lifestyle. NFL quarterback Tom Brady has famously recommended drinking around two gallons daily – nearly eight litres.

While we’re often told to drink more water to avert dehydration, constipation, kidney stones and the like, there’s clearly a dangerous level. Sustained or unexplained high water consumption is not only toxic to the body but may be a sign of an underlying health problem.

Diabetes insipidus reminds us that the term “diabetes” encompasses more than blood sugar problems. This other diabetes may be less common, but for those affected, the consequences of leaving the condition untreated may prove severe. Anyone experiencing persistent excessive thirst, water consumption, and urination should seek medical attention promptly. The cause may turn out to be sugar, hormones, or something else entirely.