There's No Such Thing As A Vitamin D Deficiency - Part One
The complex science about vitamin D levels and what they mean
Vitamin D is everyone’s favourite supplement. It’s the thing that people just know is important. While it’s hard to be sure, with a global market in the billions and a very cheap per-unit cost it’s quite likely that vitamin D is the most taken pill globally. There are just so many people out there who take a daily dose.
Most of this is based on the idea of a deficiency, or the much vaguer concept of insufficiency. We have thresholds for what constitutes “too low” when it comes to many vitamins. For vitamin D, the common wisdom is that this level is set at 20ng/ml, with an additional concern for people with levels between 20-30ng/ml which is usually called insufficiency.
The problem is, the entire idea of deficiencies are based on very weak evidence. With most conditions, we have a very strict and specific reason to set a threshold, but the basis for calling vitamin D levels of <30ng/ml too low is, and has always been, a bit vague. That’s why in 2024, the US Endocrine Society updated their guidelines and no longer recommends using the term deficiency when it comes to vitamin D levels.
In other words, there’s no such thing as a vitamin D deficiency. Or, at least, the entire idea that we should have a specific amount of vitamin D in our bloodstream is highly contested.
