Whereas toxic levels of vitamin D activity clearly promote vascular calcification by boosting absorption of calcium and phosphate, poor vitamin D status (low serum 25-hydroxyvitamin D) has been linked in observational epidemiology to increased risk for vascular calcification, in individuals with either normal or impaired renal function [166-170]. Vitamin D deficiency likewise promotes vascular calcification in rodent models [171]. Therefore, to avoid vascular calcification it may be prudent to correct either excessive or deficient vitamin D status [172]. Preferably, serum 25-hydroxyvitamin D should exceed 30 ng/mL. In those taking vitamin D regularly, hypercalcemia is unlikely until 200 ng/mL is reached; however, hypercalcemia can be seen at somewhat lower levels of 25-hydroxyvitamin D after ingestion of a massive bolus dose, or in disorders in which 1-a-hydroxylase activity is dysregulated (e.g., primary hyperparathyroidism, sarcoidosis) [173].