The Pros and Cons of Vitamin D Supplementation
Editor's note: The author will discuss the topic of this article at the National Kidney Foundation's 2013 Spring Clinical Meetings in Orlando, Fla., at an April 3 session titled “Controversies in the Management of CKD—What's Next?”
Vitamin D levels are almost universally low in patients with chronic kidney disease (CKD) and patients on dialysis.1,2 Low vitamin D levels have been associated with multiple poor outcomes in dialysis patients including all-cause mortality and faster progression of kidney disease.1,3-5
Low vitamin D levels, along with other metabolic abnormalities in CKD, such as hypocalcemia and hyperphosphatemia, lead to secondary hyperparathyroidism.Nephrologists prescribe activated vitamin D, calcitriol, or activated vitamin D analogs, such as paricalcitol and doxercalciferol, to patients with secondary hyperparathyroidism to lower parathyroid hormone (PTH) levels and prevent high turnover bone disease.
Recently, evidence has emerged suggesting that nutritional vitamin D, in the form of cholecalciferol or ergocalciferol, may also lower PTH levels. However, there may be some detrimental effects of vitamin D therapy, such as an increased risk of kidney stones and vascular calcification at very high doses.
Activated vs. nutritional vitamin D
There is controversy in the literature about the use of activated versus nutritional vitamin D.6,7 The use of activated vitamin D has been more widespread among nephrologists and its use has been associated with improved survival on dialysis and in pre-dialysis CKD.7 Because patients with end-stage renal disease (ESRD) do not have functioning kidneys, they do not convert 25-hydroxyvitamin D (the less active, circulating form) to 1,25-dihydroxyvitamin D as efficiently as patients with functional kidneys.
Separate meta-analyses of PTH suppression with either nutritional or activated vitamin D both showed statistically significant lowering of PTH levels with the respective vitamin D compound.8,9 There have been no large randomized clinical trials of vitamin D evaluating hard outcomes, such as mortality or progression of kidney disease.