Vitamin D Deficiency
And
Kidney Disease
Vitamin D deficiency has a dual relationship to chronic kidney disease.
Chronic Kidney Disease Causes Vitamin D Deficiency
Vitamin D deficiency is a common problem in patients with chronic kidney disease. As discussed earlier in Chapter 2, vitamin D is synthesized in the skin. After its production, vitamin D enters the blood stream and reaches the liver where it undergoes a chemical change known as hydroxylation. Hence, vitamin D is converted to 25 (OH) vitamin D (25 hydroxy vitamin D), also called Calcifediol. It re-enters the blood stream and reaches the kidneys where another chemical reaction (hydroxylation) takes place. At that point, 25 (OH) vitamin D is converted to 1,25 (OH)2 vitamin D (or 1,25 dihydroxy vitamin D), also called Calcitriol. It re-enters the blood stream and exerts its biochemical effects. Therefore, Calcitriol is considered the active form of vitamin D.
Now let’s examine what happens as a person develops kidney disease. The conversion of 25 (OH) vitamin D (Calcifediol) to 1,25 (OH)2 vitamin D (Calcitriol) does not take place properly. Therefore, these patients become low in Calcitriol. Chronic kidney disease causes a gradual, but progressive decline in kidney function. Therefore, the formation of Calcitriol gradually decreases. This decrease in Calcitriol causes a decrease in calcium absorption from the intestines.
However, then a compensatory mechanism kicks in: The parathyroid glands in the neck start to produce a large amount of parathyroid hormone (PTH). This large amount of PTH exerts its effects on the kidneys and enhances the conversion of 25 (OH) vitamin D (Calcifediol) into 1,25 (OH)2 vitamin D (Calcitriol). But, it comes at a price. The high amount of PTH dissolves calcium from the bones, which then become weakened. In addition, if this compensatory increase in PTH production remains unchecked, patients end up with tumors of the parathyroid glands and a high blood calcium level. For these reasons, patients on End-stage kidney disease are given Calcitriol (or its synthetic analogue) supplementation. This prevents the compensatory increase in PTH production and therefore, prevents weakening of bones and tumor formation in the parathyroid glands.
Vitamin D Deficiency Worsens Chronic Kidney Disease, Increasing Your Odds Of Ending Up On Dialysis
If you recall from Chapter 15, “Vitamin D Deficiency and High Blood Pressure,” there is a special system in the body called the Renin Angiotensin Aldosterone System (RAAS). Renin is a hormone in the body which causes production of another hormone, Angiotensin, which in turn raises blood pressure. Angiotensin also stimulates another hormone, called aldosterone, which further raises blood pressure. Aldosterone also reduces potassium in the blood.
Normal functioning of this (RAAS) system is important in maintaining blood pressure and keeping potassium in the blood in a normal range. However, when your RAAS becomes overactive, high blood pressure (hypertension) develops. An overactive RAAS and hypertension cause damage to the kidneys and are the two main culprits in the progression of kidney disease.
An overactive RAAS is often seen in people with diabetes and that’s why they often have hypertension and kidney disease as well. Currently, we use two types of drugs to deal with an overactive RAAS: ACE-inhibitors (Angiotensin Converting Enzyme inhibitors) and ARB (Angiotensin Receptor Blocking) drugs.
Now consider Vitamin D. It inhibits the RAAS by inhibiting renin and therefore, counteracts an overactive RAAS in patients with diabetes, hypertension and chronic kidney disease. Therefore, doesn’t it make sense to make sure these patients have a good level of vitamin D?
I utilize ACE inhibitors and/or ARB drugs in my patients with diabetes, hypertension and chronic kidney disease, but I also make sure that these patients have a good level of vitamin D which can also help suppress the overactive RAAS.
Unfortunately, most physicians aren’t aware of this beneficial effect of vitamin D. Consequently, vitamin D often stays low in patients with hypertension and diabetes. Many patients are not even on ACE inhibitors or ARB drugs. Unfortunately, many of these patients end up with chronic kidney disease. The sad end result is that the kidneys cease to function and they end up on dialysis.
Now you can understand why proper vitamin D supplementation in every patient with diabetes and hypertension is crucial. This simple strategy can help prevent kidney failure as well as incalculable physical, emotional and economic suffering.