Defining Hypovitaminosis D in the Elderly

Since the advent of assays for serum 25-hydroxyvitamin D (25[OH]D) many studies have reported a high prevalence of hypovitaminosis D in the elderly (1). It is essential to set criteria for hypovitaminosis D so that the means to exceed this level can be established and the progression to vitamin D deficiency requiring pharmacologic intervention averted. Definition of hypovitaminosis D as judged by assay of serum 25(OH)D poses many questions. Should the reference range for the elderly be adjusted-seasonally, and should it be similar to the values found in young adults in countries of similar latitude? Should the cut-off point be the lowest value seen in young or elderly healthy adults in summertime? Should the cut-off point be the serum 25(OH)D concentration that is associated with parathyroid hormone (PTH) levels in the young healthy adults? Should the duration of exposure to the lowest level of serum 25(OH)D be taken into consideration? Should the cut-off point be tempered by different levels of calcium intake, both from basal diet and calcium supplemented intake? Finally, should the cut-off be that which is associated with evidence of diminished fracture rate or with the improvement in bone remodeling balance?