Vitamin D is essential for bone health. However, significant controversy exists about which technology should be used to assays vitamin D levels in serum, what values constitutes evidence of insufficiency and whether vitamin D levels should be routinely determined in the general population as part of a preventative screening program. In 2010 an Institute of Medicine (IOM) panel issued guidelines, which stated that most adults 18 to 70 years old need to consume 600 IU of vitamin D per day while those older that 70 should consume 800 IU per day (1). The IOM panel also stated that total serum 25 hydroxy (25 OH )-vitamin D levels of greater than 20 ng/ml (50 nmol/l) were adequate to maintain bone health for the vast majority of people. In contrast, the Endocrine Society, while also defining deficient individuals as those with serum 25 OH vitamin D levels below 20 ng/ml, created a category of “insufficiency” to describe individuals with serum 25 OH vitamin D levels between 20 and 30 ng/ml (50 to 75 nmol/l) (2). The Endocrine Society also did not recommend routine screening for vitamin D deficiency in the general population of healthy individuals who are not at risk.
Now the United States Preventive Services Task Force has issued draft recommendations, which can be commented upon until July 21, 2014, regarding whether or not routine screening for vitamin D deficiency in the general population is desirable (3). They conclude “…that current evidence is insufficient to assess the balance of benefits and harms of screening for vitamin D deficiency”. The panel cited numerous issues, which led them to their conclusion. These include that:
1) there is no consensus definition of vitamin D deficiency, and the optimal level of total serum 25-hydroxy vitamin D is debatable.
2) there is a lack of studies using an internationally recognized reference standard. The panel found “evidence suggesting variation in results between testing methods and between laboratories using the same testing methods”. In addition recent evidence in African American populations in the United States argue strongly that serum bioavailable rather than total 25 OH vitamin D levels are a more accurate assay of vitamin D stores in individuals. However, assays for bioavailable 25 OH vitamin D are not currently readily available except in research laboratories.
3) the published evidence argued that “treatment of asymptomatic vitamin D deficiency has no benefit on cancer, type 2 diabetes, mortality in community-dwelling adults, and risk for fractures in persons not selected based on having a high risk for fracture.”
The panel did state that the risks of treating individuals with vitamin D using conventional dosing were low. However, consumption of vitamin D with calcium in conventional doses may be associated with an increased risk for kidney stones, although this does not appear to be true for treatment with vitamin D alone. In contrast, very high dosing of vitamin D, leading to total serum 25 OH vitamin D values of greater than 200 ng/ml (500 nmol/l), may cause hypercalcemia, hyperphosphatemia, suppressed parathyroid hormone levels, and hypercalciuria.
Given the current enthusiasm for vitamin D testing (the number of assays for serum 25 OH vitamin D increased by 50% between 2008 and 2009), these recommendations suggest that most physicians in general practice should first evaluate the risk that an individual might be vitamin D deficiency before ordering the test. Individuals with high risk include those with poor intake of vitamin D in food or from supplements, a history of malabsorption, a history of using medications that decrease serum vitamin D levels such as certain anti-seizure drugs or a history of limited sunlight exposure.
Farmington, CT, USA
Screening the General Population for Vitamin D Deficiency
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