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):

  1. Removing waste products from the body

  2. Removing excess water from the body

  3. Regulating salt levels in the body

  4. Producing hormones erythropoietin (responsible for production of red blood cells) and calcitriol (an active vitamin D3)

Your thyroid helps kidneys function by (3):

  1. Maintaining the correct pace blood filtration

  2. Ensuring kidneys efficiently remove water from the body

  3. 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):

  1. Reducing blood flow through the kidneys

  2. Narrowing blood vessels in the kidneys

  3. Reducing the blood filtration rate

  4. 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:

  1. You’re urinating less than usual, or your urine is foamy (this is because of a high amount of protein in the urine)

  2. You are swollen, especially around your ankles or feet (this is because the kidneys’ capacity to regulate water levels in the body is diminished)

  3. 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)

  4. You feel confused — similar to fatigue (this is caused mostly by high levels of toxins in the blood)

  5. You have shortness of breath and an irregular heartbeat (to some extent this is because the kidneys cannot regulate body electrolytes)

  6. You are anemic (this is because the kidneys are responsible for producing hormones that makes red blood cells)

  7. Dry and itchy skin (due to mineral and nutrient deficiencies)

  8. 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.

References

  1. Kaptein EM. Thyroid function in renal failure, 1986

  2. Gounden V, et al. Renal Function Tests, 2018

  3. Emmanouel DS, et al. Mechanism of impaired water excretion in the hypothyroid rat, 1974

  4. Diekman MJ, et al. Endocrine factors related to changes in total peripheral vascular resistance after treatment of thyrotoxic and hypothyroid patients, 2001

  5. Singer MA. Of mice and men and elephants: Metabolic rate sets glomerular filtration rate, 2001

  6. Klein I, et al. Thyroid hormone and the cardiovascular system, 2001

  7. Schmid C, et al. Effect of thyroxine replacement on creatinine, insulin-like growth factor 1, acid-labile subunit, and vascular endothelial growth factor, 2004

  8. Bradley SE, et al. Changes in glomerulotubular dimensions, single nephron glomerular filtration rates and the renin-angiotensin system in hypothyroid rats, 1982

  9. Zimmerman RS, et al. Cardiorenal endocrine dynamics during volume expansion in hypothyroid dogs, 1988

  10. Lo JC, et al. Increased prevalence of subclinical and clinical hypothyroidism in persons with chronic kidney disease, 2005

  11. Wiederkehr MR, et al. Correction of metabolic acidosis improves thyroid and growth hormone axes in haemodialysis patients, 2004

  12. Zoccali C, et al. Low triiodothyronine: A new facet of inflammation in end-stage renal disease, 2005

  13. Bando Y, et al. Non-autoimmune primary hypothyroidism in diabetic and non-diabetic chronic renal dysfunction, 2002

  14. Singh PA, et al. An evaluation of thyroid hormone status and oxidative stress in undialyzed chronic renal failure patients, 2006

  15. Lim VS. Thyroid function in patients with chronic renal failure, 2001

  16. Hegedus L, et al. Thyroid gland volume and serum concentrations of thyroid hormones in chronic renal failure, 1985

  17. Brohee D, et al. Circulating immune complexes in various thyroid diseases. Clin Exp Immunol, 1979

  18. Akikusa B, et al. Hashimoto’s thyroiditis and membranous nephropathy developed in progressive systemic sclerosis (PSS), 1984

  19. Dizdar O, et al. Membranoproliferative glomerulonephritis associated with type 1 diabetes mellitus and Hashimoto’s thyroiditis, 2004

  20. Feinstein EI, et al. Thyroid function in patients with nephrotic syndrome and normal renal function, 1982