How an underactive thyroid affects the kidneys
Thyroid hormones and kidney function
A certain level of thyroid hormones is necessary for your kidneys to filter out toxic substances from your blood, so proper kidney function is dependent on thyroid activity and health (1).
What do kidneys do?
Kidneys have four main functions (2):
Removing waste products from the body
Removing excess water from the body
Regulating salt levels in the body
Producing hormones erythropoietin (responsible for production of red blood cells) and calcitriol (an active vitamin D3)
Your thyroid helps kidneys function by (3):
Maintaining the correct pace blood filtration
Ensuring kidneys efficiently remove water from the body
Co-regulating salt levels in the body
An underactive thyroid can cause kidneys to have a reduced rate of recleaning toxins from the blood. Being hypothyroid further negatively affects kidney function and health by (4–9):
Reducing blood flow through the kidneys
Narrowing blood vessels in the kidneys
Reducing the blood filtration rate
Changing salt balance
All of these effects result in the swelling of the kidneys and low sodium concentration in the blood.
How kidney diseases impact the thyroid
There are several types of kidney diseases that impact thyroid function and health.
Chronic kidney disease
Patients who have chronic kidney disease often have an underactive thyroid, even without Hashimoto’s being the root cause (10).
The very first clinical sign of a kidney problem caused by an underactive thyroid is low T3 levels (11). Chronic kidney disease further affects thyroid health by:
Preventing enzyme deiodinase to convert T4 into active T3 (12).
Causing an increase in iodine levels, which prevents the thyroid gland from producing thyroid hormones (13).
Disturbing the daily rhythm of thyroid hormone production; leading to low T3 levels, slightly lower T4 levels, elevated TSH levels, and goiter (14–16).
Immune kidney diseases (glomerulonephritides)
Many different antibodies are found to be elevated in people with immune kidney diseases, similar to Hashimoto’s. Glomerulonephritis is also shown to be associated with Hashimoto’s as it leads to an underactive thyroid (17–19).
Proteinuria (high levels of protein in urine)
High levels of protein in the urine can cause kidney damage. It also causes a high loss of thyroid hormones — which are bound to protein in urine after being filtered out of the blood (20). This causes a decrease in thyroid hormone levels — so if you’re on hormone replacement therapy, you might need to take higher doses of your medication.
What are the symptoms of kidney dysfunction?
Many symptoms of kidney dysfunction are similar to those of an underactive thyroid or urinary tract infection, so recognizing a kidney problem might take some time. Here’s what to look out for:
You’re urinating less than usual, or your urine is foamy (this is because of a high amount of protein in the urine)
You are swollen, especially around your ankles or feet (this is because the kidneys’ capacity to regulate water levels in the body is diminished)
You are tired and weak (this is because the kidneys’ capacity to filter out toxins is reduced, and a high level of toxins in the body will cause fatigue and weakness)
You feel confused — similar to fatigue (this is caused mostly by high levels of toxins in the blood)
You have shortness of breath and an irregular heartbeat (to some extent this is because the kidneys cannot regulate body electrolytes)
You are anemic (this is because the kidneys are responsible for producing hormones that makes red blood cells)
Dry and itchy skin (due to mineral and nutrient deficiencies)
Muscle cramps (due to the imbalance of concentrations of sodium and potassium, aka electrolytes)
Kidney conditions are treatable with the right medical help. If you’re concerned, talk to your healthcare provider.
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