As for how high vitamin D levels need to be, the authors write that their research indicates that the optimal level of vitamin D in the blood needed to reduce diabetes risk may be higher than an Institute of Medicine committee recommendation in 2011.
“The blood 25-hydroxy vitamin D level needed to optimally reduce diabetes risk may be near and possibly above the range of 125-150 nmol/L (50-60 ng/mL) that the 2011 Institute of Medicine Committee to Review Dietary Reference Intakes for Calcium and Vitamin D provided as the range corresponding to the tolerable upper intake level (UL) of 4,000 IU/d for vitamin D,” the authors of the new paper said.
Editorialists urge caution
In an accompanying editorial also published in the Annals of Internal Medicine, Malachi J. McKenna, MD, with the department of clinical chemistry, at St. Vincent’s University Hospital, and Mary A.T. Flynn, PhD, RD, with the Food Safety Authority of Ireland in Dublin, urge caution regarding vitamin D dosing.
They write that there are important distinctions between vitamin D supplements and vitamin D therapy, and the potential harms of high-dose vitamin D are still unclear.
“Vitamin D supplementation of 10 to 20 mcg (400 to 800 IU) daily can be applied safely at the population level to prevent skeletal and possibly nonskeletal disease. Very-high-dose vitamin D therapy might prevent type 2 diabetes in some patients but may also cause harm,” they note.
Dr. Pittas said in an interview that there have been some studies with high-dose vitamin D (up to 500,000 IU a year in one study) that reported an increased fall risk in older adults who had high fall risk. “However, these findings are not generalizable to other populations that are younger and at low or average fall risk, such as the prediabetes population to which the results of this meta-analysis apply,” he noted.
“The benefit-to-risk ratio for vitamin D depends on the target population and medical condition,” Dr. Pittas said. “The editorial refers to the NAM (National Academy of Medicine) vitamin D guidelines for the general, healthy population to promote bone health. The guidelines should not be extrapolated to specific populations, for example [patients with] prediabetes,” where the vitamin D benefit-to-risk ratio would be different from that in the general population.
Dr. Pittas and colleagues caution that the people studied in this meta-analysis were at high risk for type 2 diabetes, so these results do not apply to the general healthy population. The results also should not be extrapolated to people at average risk for any type of diabetes, they add.
Several physicians either declined to comment or did not respond to requests for comment on this research.
Dr. Pittas reports the National Institutes of Health and the American Diabetes Association made payments to his institution to conduct Vitamin D-related research. He is an unpaid cochair of the Endocrine Society’s Evaluation, Treatment and Prevention of Vitamin D Deficiency Clinical Practice Guideline team.
Coauthor Dr. Jorde reports grants from Novo Nordisk Foundation, North Norwegian Regional Health Authorities, and the Research Council of Norway.
Dr. Dawson-Hughes reports she is on the DSMB for AgNovos Healthcare. AgNovos is developing a bone implant to reduce hip fracture risk and she gets a stipend from the company. She reports Helsinn Therapeutics provided anamorelin and matching placebo for an NIH-funded clinical trial.
Dr. Trikalinos was supported by the D2d study. He is a technical methodological consultant to Latham and Watkins, who is retained by Pacira Pharmaceuticals.
Dr. Angellotti has been employed by Takeda and owns stock in the company.
The editorialists report no relevant financial relationships.