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Vitamin D landscape marked by lack of consensus


 

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If you’re stumped about what to tell patients who ask you if they should be adding supplemental vitamin D to their diet, you’re not alone.

Speaker after speaker at a public conference on vitamin D sponsored by the National Institutes of Health acknowledged that there is general disagreement among well-respected scientists and medical organizations not only about recommended intakes, but about whether supplementation of vitamin D (25-hydroxyvitamin D) has any impact on ailments ranging from depression and nonspecific pain to hypertension and fall prevention.

“Most people agree that at least in high-risk individuals with osteoporosis, vitamin D has an impact on bone and skeletal health, but maybe not in those who are asymptomatic and in healthy individuals as a preventive tool,” said Dr. Clifford J. Rosen, director of clinical and translational research and a senior scientist at Maine Medical Center Research Institute, Scarborough, Me. “There seems to be growing evidence that in high-risk individuals, or in those who repeatedly fall, vitamin D may have an impact, particularly in those with very-low levels of 25-D.”

Other relationships lack conclusive randomized control data, although there are strong observational data for vitamin D’s role in preventing type 2 diabetes. Dr. Rosen is one of the investigators in a National Institute of Diabetes and Digestive and Kidney Diseases–funded clinical trial known as D2D: a study of 4,000 IU of vitamin D vs. placebo in high-risk individuals with obesity and prediabetes. The primary outcome is time to onset of type 2 diabetes. “Currently, that [trial is] in its second year and is about 30% recruited,” said Dr. Rosen, who is also a member of the FDA Advisory Panel on Endocrinologic and Metabolic Drugs. “One of the biggest obstacles to recruitment has been the constant use of vitamin D by people being screened. [They say] ‘Why should I go into a clinical trial when I’m taking vitamin D, and my doctor tells me that it will prevent diabetes?’”

The potential benefit of vitamin D intake on reducing the risk for developing cardiovascular disease, cancer, and stroke is being investigated in the NIH-funded VITAL trial. Clinicians involved in this project have enrolled more than 28,000 men and women with no prior history of these illnesses, investigating the impact of taking vitamin D3 supplements (2,000 IU/day) or omega 3 fatty acids (1 G/day).

In the meantime, current vitamin D guidance and conclusions differ among leading medical organizations. For example, the American Geriatrics Society (AGS) recommends a daily dose of 4,000 IU for fall prevention in elderly individuals. This differs from the daily dose for adults recommended by the Endocrine Society (1,500-2,000 IU), Institute of Medicine (an average requirement of 400 IU and 600-800 IU meeting the greatest need), the United States Preventive Services Task Force (600-800 IU as a fall-prevention strategy), the Standing Committee of European Doctors (600-800 IU), and the National Osteoporosis Foundation (400-1,000 IU). “How do we reconcile vitamin D intake with vitamin D levels?” asked Dr. Rosen, who is also a professor of medicine at Tufts University. “This is one of the hallmarks of the questions or problems we have, or the lack of consistency of data. We know that intakes do not reflect serum 25-D levels to a great extent.”

In addition, the terminology for serum 25-D is not clear. “Is it a deficiency? Is it a disease? What does that mean?” he asked. “More importantly, we don’t really understand what vitamin D insufficiency is. Is it a disease? Not a disease? Is it inadequate intake?”

The definition of optimal 25-D is also a matter of debate, he continued. “What’s the upper level? What does pharmacological treatment mean with respect to long-term outcomes. What is the tolerable upper limit? What is the potentially toxic limit?”

A lack of consensus also exists regarding one’s risk of vitamin D deficiency. For example, the AGS puts this risk at less than 30 ng/mL, the Endocrine Society at less than 20 ng/mL, and the Institute of Medicine at less than 12 ng/mL. “We have a lot of inconsistency in the data,” Dr. Rosen concluded. “There’s not unanimity in recommendations, even among so-called experts.”

Dr. Peter Millard

Dr. Peter Millard

During the same session, Dr. Peter Millard presented findings from a national analysis of vitamin D level testing in adult patients conducted from January 2013 to September 2014. The sample, drawn from Athenahealth integrated electronic health records (EHRs), included more than 6,000 internists and family physicians and 2,000 nonphysician clinicians, translating into an estimated 900,000 patient encounters per month. During that time period 4%-5% of all adult patient encounters were associated with a vitamin D test ordered.

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