Vitamin D in Kidney Disease

Chemical structure of cholecalciferol, aka vitamin D3. (Photo credit: Wikipedia)

photo credit: aluzano

The authors of a recent study in the clinical journal of the american society of nephrology has suggested that vitamin d may have a role in reducing proteinuria in chronic kidney disease. Previously the main stay of therapy for protein in the urine or proteinuria has been the use of a class of drugs known as A.C.E inhibitors (ACEI). This newly discovered effect of vitamin D occurs in addition to the effect of ACEI on proteinuria. This implies that vitamin D supplementation may be a possible adjunctive therapeutic option in patients with kidney disease and proteinuria. Vitamin D may also reduce the loss of a vital class of cell within the kidney, the ever more important podocyte. This cell class is involved multiple diseases affecting the kidneys ability to retain protein in the blood. Dysfunction of the podocyte has been cited as being responsible for some types of inherited causes of kidney failure. In addition blood pressure, the sensitivity of the body to insulin as well as inflammation are all improved by vitamin D.

The authors note that although only few studies exist, the data suggests that this is an area worthy of further research, with previous studies in pre-dialysis patients showing similar findings as above. The decrease in proteinuria due to vitamin D has also been shown to occur in patients with IgA nephropathy in one study of 10 patients, it was also accompanied by decreased levels of chemicals responsible for the development of scarring in the kidney. The development of fibrosis or scarring occurs as a final pathway of injury in many diseases that affect the kidney including diabetic kidney disease. Diabetic kidney disease is perhaps the most common cause of kidney failure requiring dialysis. As such if vitamin D supplementation should be able to have even a small impact on the survival of kidneys of patients with diabetic kidney disease the resultant decrease in spending on dialysis would save millions of US dollars each year.

Several mechanisms have been suggested for the positive action of vitamin D in kidney disease. Chief among these is the notion that the vitamin acts as a hormone at the level of specific tissues and organs of the body where it influences immunity, vascular function cardiac function and muscle function. It also acts on the immune system to turn off inflammation. These are all effects that would benefit patients with kidney disease.

These are truly interesting times for Vitamin D.

Vitamin D in Health and Kidney Disease.

Overview of calcium regulation (See Wikipedia:Calcium in biology). To discuss image, please see Talk:Human body diagrams References Page 1094 (The Parathyroid Glands and Vitamin D) in: Walter F., PhD. Boron (2003). Medical Physiology: A Cellular And Molecular Approaoch, 1300, Elsevier/Saunders. (Photo credit: Wikipedia)

photo credit: photofarmer

Vitamin D is an essential hormone in both health and disease, it is obtained from both dietary sources as well as direct sunlight via a process that occurs in the skin involving ultraviolet radiation. Foods that are high in vitamin D include oily fish, the ingestion of which is capable of preventing vitamin D deficiency. Measurement of vitamin D levels to determine if you have adequate amounts of the vitamin within your body is difficult as there is no consensus on the amount of vitamin D that is appropriate for all individuals. Broad guidelines that are capable of identifying very low levels as insufficient and very high levels as toxic are probably inadequate moving forward and will likely be revised when a more narrow and useful band is obtained.

Vitamin D is related to parathyroid hormone which controls the formation of bone and is now thought to be responsible for vascular health via mechanisms that are still to be worked out. Vitamin D either by direct methods or through its effect on parathyroid hormone should therefore play a role in cardiovascular disease.

Abnormalities in both vitamin D and parathyroid hormone have been cited in the press as being responsible for abnormalities that include cognitive dysfunction, muscle and bone abnormalities and cardiovascular effects. The bulk of the research into vitamin D and parathyroid hormone is obtained from the nephrology literature where its role in metabolic bone disease is well established and its emerging role in cardiovascular disease is being investigated in the dialysis and Chronic Kidney Disease population. It is intriguing that vitamin D's important in the normal population may have been overlooked for so long.

For years the general population has had an increasing incidence of cardiovascular disease diabetes and metabolic syndrome, which has largely been driven by obesity as well as increasing rates of some cancers. Some researchers now speculate that the finding of abnormally low vitamin D in these groups may be more important than previously thought and may imply a causative role of vitamin D. This would place the vitamin at the center of multiple processes that do not seem related on the surface, implying a deeper level of complexity in terms of its involvement with metabolic processes that was unsuspected.


photo credit: aresauburn™.

One author speculates that many of the findings in the normal population have been under our noses the entire time in CKD patients

The findings of cardiovascular disease increased cancer and metabolic syndrome in some part may be considered a part of the aging process with the body becoming progressively more unable to heal entirely with time. The previosuly mentioned problems of cardiovascular disease and metabolic syndrome are prevalent among patients with chronic kidney disease, this was previously thought to be due to the presence of toxins that are not adequately excreted by the failing kidney. But if we think of CKD as a process of accelerated aging and compare vitamin D levels between the normal population and CKD population then the hypothesis that vitamin D may play a central role in the aging process and hence affect multiple systems simulataneously becomes more plausible.

Studying this moving forward will be challenging due to the fact that we are still in the relative infancy of vitamin D research. What does one measure to determine the effect of vitamin D ? which one of the vitamin D's do you measure (of which there are several), what is the normal range for these measurements? Which one of the vitamin D's do you supplement with and how does that affect levels of the other vitamin D's.

However, research is ongoing, studies have demonstrated that positive effects can be obtained by supplementing greater than 700 iu per day, with some reduction in cancer risk and fracture rates. Supplementation with an activated form of vitamin D has also been shown to decrease protein excretion in patients with CKD this may translate into more years off of dialysis for patients with progressive nephropathy something everyone would like to see.



UPDATE: 12/4/12
Related articles

• Vitamin D treatment not found to reduce cardiovascular abnormalities in kidney disease patients (eurekalert.org)
• Vitamin D treatment not found to reduce cardiovascular abnormalities in kidney disease patients (medicalxpress.com)