Excessive thirst (polydipsia) may be a completely innocent symptom, but on the other hand it may accompany many diseases. Feeling of thirst is by humans controlled by brain. Brain centers monitor the concentration of dissolved substances in the blood. When this concentration is elevated because of fluid deficiency, brain sends us unpleasant perception of thirst to force increased fluid intake.
Excessive thirst is usually a response to dehydration, i.e. excessive loss of fluid.
Diabetes is associated with increased levels of blood sugar (glucose). This level may be so high that glucose molecules begin to leak into urine. Glucose molecules in urine pick up fluid and ions. The first symptom of untreated diabetes is therefore excessive urination leading to dehydration and this is followed by thirst. Yet the thirst is usually perceived as the major symptom by majority of patients.
This is a rare endocrine disease linked to the antidiuretic hormone that is produced in the brain. Antidiuretic hormone affects kidney tissue and prevents excessive fluid loss into urine. If production of this hormone decreases or when kidney tissue stops to respond, the consequences are similar – urine production is sharply increased (sometimes over 10 to 15 liters of urine per day).
Note: A short-term decline of antidiuretic hormone occurs also due to alcohol consumption. Therefore, person after a few beers often suffers from thirst and mild dehydration (despite fluid taken in beer) because of excessive urination.
This is an autoimmune disease that is accompanied by impairment of the salivary and lacrimal glands. The sensation of thirst occurs in dry mouth during long-term lack of saliva. Dry mouth is in Latin described as xerostomia.
Nervous people, mentally labile individuals, people under stress or some psychiatric patients may feel thirsty, drink more, and then, quite naturally, more frequently urinate. Complaints about thirst and excessive drinking in this case mimic symptoms of diabetes. The difference is that thirst occurs initially and frequent urination is its result. In diabetes, the problem is opposite as mentioned above.
Situations related to excessive fluid output
These include fever, physical activities, warm environment, greater blood loss, etc. Dehydration usually causes increased thirst. When the condition is solved by increased fluid intake, feeling of thirst disappears with subjective relief.
Excessive ions intake
Larger amount of salt causes increase of sodium concentration in blood. The brain notices these changes and creates feeling of thirst to cause dilution. When increased fluid intake follows, the brain is indeed satisfied, but excessive amount of water is present in blood vessels causing elevation of blood pressure. For this reason, people with high blood pressure shall reduce meal salting.
This is a rare genetic disease where functionally impaired kidney tubules result in loss of ions and fluid into the urine. Excessive fluid loss leads to thirst.
The most common illness accompanied by strong thirst is diabetes. We have to distinguish it from psychogenic thirst, in ideal case by urinalysis (glucose in urine) and basic blood test (glucose concentration in blood). If there is elevated blood sugar and present glucose in the urine, diabetes is a very suspicious diagnosis. Diabetes insipidus may be investigated by administration of artificially produced antidiuretic hormone.
Abnormally excessive long-term thirst - especially if it is associated with excessive urination - is a good reason to visit a doctor. Urinalysis and blood sugar examination shall be made.