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Vitamin D Deficiency in Kidney Disease

Oct 6, 2023
 

Many people are deficient in Vitamin D. The Centers for Disease found that more than 50% of Americans have low levels of vitamin D, and roughly 35% of adults have a vitamin D deficiency.

Chronic kidney disease (CKD) is an increasing burden on the healthcare system. Vitamin D deficiency is common in CKD patients due to decreased kidney function. Growing evidence shows that vitamin D deficiency may contribute to reduced kidney function and CKD progression.

Key Points

  • Kidney disease, or CKD, is a growing burden on healthcare systems due to its increasing prevalence and the characteristics of the disease.
  • Research has provided an increased understanding of the clinical and biological results of the relationship between vitamin D deficiency and CKD.

Vitamin D Overview

Vitamin D is a fat-soluble vitamin that is naturally only present in very few foods. Two forms of inactive vitamin D occur naturally: vitamin D2 (ergocalciferol), which is derived from nonanimal sources, and vitamin D3 (cholecalciferol), which is derived from the skin and animal products.

Through two steps, the liver and kidney convert these inactive forms of vitamin D into their active forms. In the first step, inactive forms of vitamin D2 and vitamin D3 are first moved to the liver by vitamin D-binding proteins, where they undergo hydroxylation to become the main circulation form of vitamin D.

The second step of vitamin D activation occurs in the kidneys and involves a second hydroxylation.

Sources of vitamin D may include:

  • Sun exposure
  • From your diet and fortified foods
  • Through dietary supplements

Vitamin D has several essential functions in the body that it is responsible for, such as:

  • Regulating the absorption of phosphorus and calcium
  • Facilitating regular immune system function
  • Preventing osteomalacia in adults and rickets in children
  • Maintaining and building strong and healthy bones
  • Suppressing the release of parathyroid hormone, which causes bone resorption (breakdown)
  • Reducing inflammation

What causes vitamin D deficiency?

Vitamin D deficiency typically occurs when the body is not correctly using or absorbing active or inactive forms of vitamin D and when Vitamin D consumption is insufficient in the diet or from sunlight.

Several specific causes of vitamin D deficiency include medical conditions such as kidney disease or liver disease, weight-loss surgeries, and certain medicines.

Environmental and biological factors, such as age, race, and the amount of melanin in the skin, may increase the risk of a person developing vitamin D deficiency.

Complications of vitamin D deficiency

Vitamin D insufficiency is common and is characterized as a vitamin D level that is lower than normal and presents with no symptoms or visible signs.

As many foods and drinks have become fortified with vitamin D, severe complications have become less common. Severe complications of vitamin D deficiency may include:

  • Rickets (softening of the bones during childhood)
  • Hypocalcemia (low blood calcium)
  • Hypophosphatemia (low blood phosphate)
  • Osteomalacia (softening of bones in adults)

Diagnosis

A healthcare provider or nephrologist may order a blood test to measure vitamin D levels if the patient has certain medical conditions, risk factors, or vitamin D deficiency symptoms. The most common blood test for vitamin D deficiency is the 25-hydroxyvitamin D [25(OH)D].

Vitamin D Deficiency and Kidney Disease

Vitamin D deficiency in CKD patients is an increasing health issue. The prevalence of vitamin D is higher in CKD patients than in the general population.

How does CKD cause vitamin D deficiency?

The kidneys play an essential role in vitamin D level regulation and metabolism in the bloodstream. Healthy kidneys are full of vitamin D receptors, and they are required to convert vitamin D into its active form. Across all stages of CKD, the kidneys lose their ability to activate vitamin D.

CKD reduces the amount of specific enzymes from the kidney (1-alpha-hydroxylase) that are required in the last step of turning inactive vitamin D into its active form. This can lead to a reduced level of usable (active) vitamin D in the body.

The changes that CKD causes in vitamin D metabolism, phosphate, and calcium regulation, and bone metabolism may lead to CKD metabolic bone disease (CKD-MBD).

Research suggests several mechanisms may be involved in the reduced production of active forms of vitamin D that occur over the course of CKD progression:

  • A decrease in kidney weight due to damage limits the amount of chemicals needed to produce active vitamin D products.
  • A reduction in glomerular filtration rate (GFR) may also result in decreased production of active vitamin D products.
  • Another factor that may cause low vitamin D status during CKD progression is the increase in fibroblast growth factor 23 levels. This may directly suppress the activity and expression of chemicals required to convert inactive vitamin D into its active form.

How does vitamin D deficiency affect CKD?

In pre-dialysis or dialysis CKD patients, vitamin D insufficiency or deficiency is a common condition.

When there are low levels of vitamin D and the kidneys begin to fail, the body absorbs less calcium. This causes calcium blood levels to become low. Low calcium blood levels signal the parathyroid glands to produce more parathyroid hormone, and they increase in size. This results in a condition called secondary hyperparathyroidism.

Vitamin D deficiency also increases the risk of CKD patients and the general population developing heart disease.

Vitamin D supplementation for dialysis patients

If a CKD patient has a high PTH, a healthcare provider may prescribe an activated vitamin D to suppress the increased PTH production. Patients on hemodialysis may receive their vitamin D prescription intravenously during dialysis treatment.

Patients on peritoneal dialysis or those not on dialysis may be prescribed an oral form of generic calcitriol or active vitamin D. Healthcare providers will regularly check PTH levels to ensure that the treatment is working and that PTH production is not over-suppressed.

Further research is required to uncover potential renoprotective mechanisms of vitamin D treatment for CKD patients.

Talk to your healthcare provider or nephrologist before taking any vitamin D supplements, as there are many different types of vitamin D supplements. Your healthcare provider will tell you the amount and type of vitamin D that you should take.

Panoramic Health

Panoramic Health is an integrated value-based kidney care platform that is led by physicians. We have 14 years of experience managing patient outcomes using care management tools, predictive analytics, and the largest live CKD database in the United States.

Our patients receive holistic care management from our care coordination team and nephrologists. This provides patients with industry-leading care that may slow disease progression, increase quality of life, and help them manage their health’s full spectrum.