There's No Such Thing As A Vitamin D Deficiency - Part 3

Does anyone really need to take a supplement?

Pictured: Entirely unnecessary? Photo by Marco Palumbo on Unsplash

This is the third installment of my series looking at vitamin D supplementation and the 2024 Endocrine Society guidelines. In the first section, we looked at why there is no such thing as a vitamin D deficiency. In the second, we discussed why the recommendation for people over 75 to take a vitamin D supplement regardless of blood levels is very debatable.

For the last two parts, we are going to look at much more problematic issues in the remaining recommendations. To recap, the Endocrine Society currently recommends that four groups of people take a vitamin D supplement:

1. People over 75

2. People under 18

3. Pregnant people

4. People with prediabetes

For people over 75, the recommendation makes a bit of sense. It is based on very weak data, but there’s ~some~ possibility that vitamin D pills will add a month or two to your life if you start taking them the day you turn 75. They aren’t harmful, so on balance it’s not the worst idea.

For the other groups, the data is…much worse. The issue is fairly simple—in all three cases, there are serious concerns about the trustworthiness of the studies used to make the recommendations. Trustworthiness, or reliability, is the term we use when we find mistakes, errors, and similar in scientific research. These sorts of errors can be caused by anything from simple data mismanagement to outright fraud, but they always mean that we should not use the study in question as evidence of anything.

So let’s look at the recommendations for pregnant people, kids, and people with prediabetes, and why the evidence does not support these groups taking vitamin D supplements.

Pregnancy

The first group we should tackle is pregnancy, because it’s the easiest one to deal with. I’ve recently written about the issue of fraud, misconduct, and trustworthiness in the women’s health space. The question of whether pregnant people should receive vitamin D supplementation falls squarely into the area of women’s health research where there are innumerable studies that are extremely problematic.

The Endocrine Society recommends that people take a vitamin D supplement during pregnancy due to the “potential to lower risk of preeclampsia, intra-uterine mortality, preterm birth, small for gestational age birth, and neonatal mortality”. Specifically, the systematic review and meta-analysis that the society did for their updated guidelines found:

1. No benefit for preeclampsia

2. No benefit for intra-uterine mortality

3. No benefit for preterm birth

4. No benefit for small for gestational age birth

5. No benefit for neonatal mortality