How Helpful Is Vitamin D in Prediabetes?

Thatched Cottages in the Sunshine Reminiscence of the NorthVitamin D is an illusory panacea. Popular fascination with this “sunshine vitamin” has drawn people to latch onto associations that it has with many conditions. But those associations, when tested, often turn out to be confounded. So does a new systematic review and meta-analysis of vitamin D in prediabetes tell a different story?

Anastassios Pittas and colleagues think so. Based upon their analysis, they offer a rather unqualified conclusion:

“In adults with prediabetes, vitamin D was effective in decreasing risk for diabetes.”

A Small Effect

We like an elegant conclusion, but unfortunately, this one leaves out an important fact. The effect is very modest. In fact, lifestyle changes in the diabetes prevention program (DPP) study had roughly four times greater effect than vitamin D in this analysis. To prevent one case of prediabetes from progressing to a diagnosis of type 2 diabetes, 30 people would have to take a vitamin D supplement. By comparison, only seven people have to follow the DPP lifestyle program to prevent a case of diabetes.

Lifestyle change in the DPP hardly wins acclaim for overwhelming effectiveness, and yet, vitamin D supplementation is far less effective.

In a companion editorial, Malachi McKenna and Mary Flynn pointed to the outcomes of the three studies that provided the data for this meta-analysis. Not one of them showed a benefit by itself. Pittas et al dismiss that concern. They say the individual studies “underpowered” to detect the effect of vitamin D.

We have a different view – the effect is underwhelming.

Click here for the study, here for the editorial, and here, here, and here for further perspective.

Thatched Cottages in the Sunshine Reminiscence of the North, painting by Vincent van Gogh / WikiArt

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February 9, 2023