How does thirst work and when is it excessive?
The thirst center in the hypothalamus responds to the concentration of salts in the blood and the volume of circulating fluid. When the blood thickens just a fraction of a percent, the desire to drink kicks in, and the hormone vasopressin causes the kidneys to retain water. Normally, a person needs about one and a half to two liters of fluid per day, adjusted for heat and stress. Polydipsia is said to occur when there is a persistent excess of the usual volume, when thirst is not quenched and is accompanied by the same copious urine output.
- Thirst increases in the heat and during physical activity - this is the norm.
- The thirst that wakes you up at night is alarming
- The volume of urine is important, not just the frequency of trips to the toilet
- Dry mouth without a lot of urine is a separate situation
Diabetes mellitus is the number one cause
When glucose levels are high, the kidneys do not have time to return sugar to the blood; it comes out in the urine and pulls water with it. A vicious circle arises: excessive urination - dehydration - thirst. In type 1 diabetes, complaints increase over weeks and are accompanied by weight loss; in children, bedwetting often returns. In the second type, the picture is blurred, thirst may be the only noticeable sign. That is why, with constant thirst, a glucose test is taken first.
- Thirst and excessive urination, including at night
- Losing weight with normal or increased appetite
- Dry skin and mucous membranes, itching
- Slow wound healing
- Recurring thrush and boils
- Deterioration of vision, feeling of fog before the eyes
Other causes of constant thirst
If sugar is normal, the search circle expands. Diabetes insipidus is associated with a lack of vasopressin or insensitivity to it: a lot of urine is released, but it is light and light. High levels of calcium in diseases of the parathyroid glands also cause thirst and weakness. Thirst is caused by chronic kidney disease, taking diuretics and lithium drugs, dehydration due to vomiting and diarrhea. There is also primary polydipsia, when a person drinks a lot out of habit or due to anxiety, and the kidneys simply excrete the excess.
- Diabetes insipidus
- Increased blood calcium
- Chronic kidney disease
- Diuretics and lithium
- Dehydration due to vomiting, diarrhea, fever
- Primary polydipsia due to anxiety
Dry mouth is not always thirst
Many describe thirst as a feeling of stickiness and dryness in the mouth, although the volume of urine is normal. This condition is most often associated with a decrease in saliva production: taking medications with a drying effect, breathing through the mouth with a stuffy nose, smoking, age-related changes, Sjögren's syndrome. A simple guideline helps to distinguish: with true thirst, water brings relief and the amount of urine increases; with dry mouth, water moistens the mucous membrane, but the desire to drink returns almost immediately.
- Stuffy nose and mouth breathing
- Antihistamines, diuretics, antidepressants
- Smoking and dry air
- Sjögren's syndrome
- Radiation therapy to the head and neck area
What tests to take and what to do
The examination begins with fasting blood glucose and glycated hemoglobin - they either confirm diabetes or eliminate the question. Urinalysis shows sugar, ketones and density, and low density indicates diabetes insipidus. Calcium, creatinine and electrolytes complete the picture. Before visiting a doctor, it is useful to keep a diary: how much liquid you drink and how much urine you pass during the day. You cannot limit yourself in drinking when you are very thirsty - this is dangerous due to dehydration.
- Fasting blood glucose
- Glycated hemoglobin HbA1c
- General urine analysis with density
- Blood calcium and creatinine
- Diary of fluid intake and urine volume
- Review your medications with your doctor
