Hypothyroidism, also known as underactive thyroid, is a condition in which the thyroid gland does not produce enough of the thyroid hormones T3 and T4. Thyroid hormones play an important role in regulating many body functions, including urine output. So does hypothyroidism affect urine output? Let’s take a closer look.
Overview of hypothyroidism
The thyroid gland is a small, butterfly-shaped gland located at the base of the neck. It produces two main hormones – triiodothyronine (T3) and thyroxine (T4). These hormones circulate in the blood and affect nearly every cell and tissue in the body. They help regulate growth, development, metabolism, body temperature, heart rate, and many other functions.
In hypothyroidism, the thyroid gland does not make enough thyroid hormones to meet the body’s needs. This can happen for several reasons:
- Hashimoto’s disease – an autoimmune disorder where the immune system attacks and damages the thyroid gland.
- Thyroiditis – inflammation of the thyroid gland.
- Surgical removal of part or all of the thyroid gland.
- Radiation treatment of the thyroid gland.
- Certain medications.
- Congenital (birth) defect.
- Iodine deficiency.
Whatever the cause, the result is that the body lacks sufficient thyroid hormones. This causes many of the body’s functions to slow down. Symptoms of hypothyroidism can include fatigue, weight gain, dry skin, hair loss, feeling cold, muscle weakness, constipation, slowed heart rate, depression, and impaired memory.
How thyroid hormones affect kidney function and urine output
Thyroid hormones affect nearly every system in the body, including the kidneys. The kidneys are responsible for filtering waste from the blood and regulating water and electrolyte balance in the body. Normal thyroid function is important for the kidneys to work properly.
Here are some of the ways thyroid hormones influence kidney function and urine output:
- Increasing glomerular filtration rate (GFR) – T3 stimulates the kidneys to increase GFR, which is the rate at which the kidneys filter blood. A higher GFR leads to more urine output.
- Increasing renal blood flow – Thyroid hormones cause vasodilation of blood vessels in the kidneys, increasing renal blood flow. More blood flow allows the kidneys to filter more fluid.
- Stimulating renin release – Renin is an enzyme produced by the kidneys that helps regulate blood pressure and fluid balance. Thyroid hormones increase renin release, which leads to increased sodium retention and fluid reabsorption by the kidneys.
- Increasing number of aquaporins – Aquaporins are proteins that act as water channels in the kidneys, allowing water reabsorption. T3 stimulates aquaporin production, increasing water reabsorption and decreasing urine output.
- Regulating electrolyte pumps – Thyroid hormones help regulate pumps like the sodium-potassium ATPase pump. This helps control sodium reabsorption in the kidneys.
In summary, thyroid hormones directly stimulate kidney function, glomerular filtration, renal blood flow, and electrolyte reabsorption. This allows the kidneys to regulate fluid balances in response to the body’s metabolic needs.
Kidney effects of hypothyroidism
Since thyroid hormones are so important for normal kidney function, it’s not surprising that hypothyroidism can impair kidney function and urine output. Some of the major kidney effects of hypothyroidism include:
- Decreased GFR – Studies show hypothyroidism causes a decreased glomerular filtration rate, indicating the kidneys are not filtering blood normally.
- Impaired water handling – Hypothyroidism impairs the kidneys’ ability to concentrate and dilute urine optimally.
- Hyponatremia – Low thyroid levels can lead to hyponatremia (low blood sodium), due to impaired free water clearance.
- Increased creatinine – Mild elevations in serum creatinine may occur, indicating reduced kidney function.
- Proteinuria – Some patients with hypothyroidism develop protein in the urine.
- SIADH – The impaired water handling sometimes seen can lead to SIADH (syndrome of inappropriate antidiuretic hormone secretion).
- Electrolyte imbalances – Abnormal sodium, potassium, and calcium levels are more common in hypothyroid patients.
Fortunately, these kidney impairments are often reversible once the hypothyroidism is treated and thyroid hormone levels are restored to normal.
Hypothyroidism leads to reduced urine output
Given the important effects of thyroid hormones on the kidneys, it’s clear hypothyroidism ultimately reduces urine output. Without enough T3 and T4, many of the kidney’s functions are suppressed. Here are some of the mechanisms that lead to decreased urine production:
- Lower GFR due to decreased renal blood flow and filtration pressure.
- Reduced water and salt pumping due to lower activity of channels and transporters.
- Decreased aquaporin channels for water reabsorption.
- Impaired renin-angiotensin system reduces glomerular pressure.
- Blunted response to antidiuretic hormone (ADH).
These combined effects result in both decreased fluid filtration and reduced reabsorption by the kidneys. This double hit leads to an overall reduction in urine volume produced.
Research on hypothyroidism and urine output
Several studies have looked specifically at urine output in hypothyroid patients compared to healthy controls. Some key findings include:
- One study of 23 women with hypothyroidism found they excreted an average of 1.3 liters of urine daily, compared to 1.7 liters in healthy women. Their kidneys’ concentrating ability was also reduced.
- A study in hypothyroid rats found significantly decreased glomerular filtration rate, urine flow, and electrolyte excretion.
- Multiple studies show impaired urinary dilution and concentration in hypothyroidism, with decreased free water clearance.
- Hypothyroid patients have been found to have an impaired response to vasopressin, which helps regulate urine volume.
- Treatment with levothyroxine has been shown to increase urine output towards normal as thyroid hormone levels are restored.
Overall, the research clearly demonstrates that hypothyroidism impairs normal urine production due to both decreased filtration and reduced tubular reabsorption in the kidneys.
Other potential causes of increased urine output in hypothyroidism
Although hypothyroidism itself reduces urine output, there are a few factors that can cause excessive urination in someone with low thyroid levels:
- Medications – Some medications used to treat hypothyroidism’s symptoms like diuretics and antidepressants may increase urine volume.
- Hyperglycemia – Uncontrolled diabetes causing high blood sugar leads to increased urine output.
- SIADH – The impaired water handling in hypothyroidism can sometimes paradoxically cause increased urine diluteness and frequency.
- Heart failure – Severe hypothyroidism can impair heart function, leading to increased urine output.
However, these causes of increased urination are consequences of hypothyroidism itself or its treatment, not direct effects of reduced thyroid hormones. The underlying effect of low T3 and T4 levels is to decrease urine production.
Conclusion
In summary, there is strong evidence that hypothyroidism impairs normal kidney function and reduces urine output. Thyroid hormones are critical for regulating glomerular filtration, renal blood flow, electrolyte pumps, and aquaporin water channels in the kidneys. Without enough T3 and T4, both the filtration and reabsorption functions of the kidneys become impaired.
Research studies have confirmed reduced 24-hour urine volumes in hypothyroid patients compared to healthy individuals. Treatment to restore thyroid hormone levels can reverse these impairments in kidney function and urine output. So while uncontrolled diabetes or medications may sometimes cause excessive urination, the direct effect of hypothyroidism itself is to decrease urine production due to reduced kidney function.