In a single center observation study of 43 pre-dialysis chronic kidney disease patients (stages 1–5) and 103 patients undergoing hemodialysis, inadequate levels of 25-(OH)D (<30 ng/mL) was found in 86.0% of the former and 97% of the latter with no correlation of 25-(OH)D levels with either albumin or parathyroid hormone levels [58]. Here, PTH is linked to chronic kidney disease.