Low vitamin D status: definition, prevalence, consequences, and correction

Abstract

Vitamin D is obtained from cutaneous production when 7-dehydrocholesterol is converted to vitamin D(3) (cholecalciferol) by ultraviolet B radiation or by oral intake of vitamin D(2) (ergocalciferol) and D(3). An individual's vitamin D status is best evaluated by measuring the circulating 25-hydroxyvitamin D (25(OH)D) concentration. Although controversy surrounds the definition of low vitamin D status, there is increasing agreement that the optimal circulating 25(OH)D level should be approximately 30 to 32 ng/mL or above. Using this definition, it has been estimated that approximately three-quarters of all adults in the United States have low levels. Low vitamin D status classically has skeletal consequences such as osteomalacia/rickets. More recently, associations between low vitamin D status and increased risk for various nonskeletal morbidities have been recognized; whether all of these associations are causally related to low vitamin D status remains to be determined. To achieve optimal vitamin D status, daily intakes of at least 1000 IU or more of vitamin D are required. The risk of toxicity with "high" amounts of vitamin D intake is low. Substantial between-individual variability exists in response to the same administered vitamin D dose. When to monitor 25(OH)D levels has received little attention. Supplementation with vitamin D(3) may be preferable to vitamin D(2).

Copyright 2010 Elsevier Inc. All rights reserved.

Figures

Figure 1. Spectrum of Vitamin D Status

The spectrum of low vitamin D status is depicted. At very low vitamin D levels, (25[OH]D of approximately 10 ng/ml or below) calcium malabsorption, osteomalacia/rickets and myopathy occur. Less marked vitamin D deficiency (often referred to as inadequacy or insufficiency) has been associated with a variety of adverse health consequences. Consensus regarding an “optimal” 25(OH)D concentration continues to evolve, however there appears to be increasing agreement that values above approximately 30-32 ng/ml are associated with optimal physiologic function.

Figure 2. Distribution of Serum 25(OH)D in Highly Sun-exposed Adults

In these two studies in which the average total body sun exposure was approximately 11 hours per week, a broad, and somewhat Gaussian, distribution of circulating 25(OH)D is apparent. Data adapted from Binkley, et. al., and Barger-Lux, et. al. Note that the Barger-Lux, et. al., study utilized a 25(OH)D assay that measures approximately 10% higher than the HPLC assay used in the Binkley, et. al., report.

Figure 3. Prevalence of Low Vitamin D Status in Various Populations

In these recent cohort studies, low vitamin D status, whether defined as a 25(OH)D below 20 ng/ml or below 30 ng/ml is extremely common. Data adapted from various sources., -

Figure 4. Variable Response to Daily Vitamin D3

In these seven Caucasian older adults (age 66-88 years), all of whom started the study with a 25(OH)D level less than 30 ng/ml, the variable response to daily administration of 1,600 IU vitamin D3 is apparent.