This month (Feb 2023) Pittas and colleagues from Tufts published a systematic review article article in Annals of Internal Medicine about the possible value of Vitamin D in delaying diabetes onset (“Vitamin D and Risk for Type 2 Diabetes in People With Prediabetes A Systematic Review and Meta-analysis of Individual Participant Data From 3 Randomized Clinical Trials”).

Data from 3 studies was evaluated in which “high dose” varied from 20,000 IU (international units) of D3 a week to 4,000 IU of D2 daily to 0.75 mcg of eldecalcitol daily (which is 500 mcg). I’ve talked before about the fact that a math error might mean that the Institute of Medicine (IOM) minimum daily requirement recommendations for Vitamin D were set way too low. A new look at old data suggested that the daily dose should be closer to 8,000 IU, so a weekly dose of 20,000 IU only qualifies as “high dose” based on the current (perhaps mistaken) recommendations. I’ve also talked about the fact that most patients with chronic wounds have a low Vitamin D (25-hydroxy) level and that they often heal when that level is normalized.

Early COVID-related deaths were linked to low Vitamin D. There are a lot of reasons to take more Vitamin D (and that means D3) than the IOM recommended dose. Now there’s another one – it might stave off diabetes in Prediabetics.

Because the Annals article is behind a paywall, I am providing the link to the summary from MedPage Today.

You can read the details yourself, but the short version is that a meta-analysis of three randomized clinical trials showed that vitamin D supplementation reduced the risk for type 2 diabetes by 15% in people with Prediabetes in a model adjusted for age, gender, body mass index (BMI), race, and HbA1c. Those who took vitamin D supplementation had a 30% increased likelihood of returning to normal glucose levels. This translated to a 3.3% absolute risk reduction over the course of 3 years – which is a big deal economically and medically. In followup (excluding those who stopped the D supplement, started diabetes medication or lost weight), the individuals who just kept taking the supplement continued to be protected from diabetes.

However, authors Malachi McKenna, MD, of University College Dublin, and Mary Flynn, PhD, RD, of Food Safety Authority of Ireland, Dublin, pointed out that on their own, all three of these trials found similarly nonsignificant diabetes risk reductions associated with vitamin D supplementation –- so it’s fair to ask how much this plan would really work. Having said that, there are so many other reasons to take Vitamin D supplementation (if you don’t have kidney disease – if you do, ask your nephrologist) that it’s worth considering. What annoys me is how hard it is to get insurance to cover a darn Vitamin D level. It’s easier to get a drug screen. What should we do about that?