“The worthlessness of vitamin D is mildly exaggerated” by dynomight

For a while there, many people thought vitamin D was magical—that it could improve bones, the heart, infections, cancer, heart disease, longevity, even mental health. But among people I respect, opinion is now overwhelmingly that taking vitamin D does nothing unless you're severely deficient. The central argument is that while vitamin D levels are correlated with ~all positive health outcomes, when you actually test vitamin D supplements against placebo in randomized trials, nothing ever happens. That's what I used to think, too. But I've come to think the skeptics have over-corrected. Yes, randomized trials have shown the magical correlations are not causal. But if you start with non-insane expectations, the trials look like weak but positive evidence. And if you consider what we know about biology and evolution, I think the balance of evidence tips pretty clearly in the direction that people with low-ish levels would be wise to supplement. Am I certain that vitamin D is beneficial for people with low-ish levels? Absolutely not! But I claim that's the best bet given the limits of our knowledge. The classical view: Boring bone vitamin Most vitamins are "ingredients" that the body uses to do stuff. Vitamin D is more [...] ---Outline:(01:19) The classical view: Boring bone vitamin(04:28) The correlation view: Magical mystery cure(07:58) Meanwhile in biology(11:10) Then came the RCTs(15:12) I made some tables(16:32) Squinting at the data(22:24) Where are we?(23:15) The case for supplementing anyway(23:19) It's biologically plausible that vitamin D is good(24:40) Humans evolved to have a lot of vitamin D(27:14) What do you expect from vitamin D?(29:22) What do you expect from vitamin D trials?(31:11) The trials do find slightly helpful numbers(32:50) You're probably already taking vitamin D(34:34) So that's my story The original text contained 35 footnotes which were omitted from this narration. --- First published: June 23rd, 2026 Source: https://www.lesswrong.com/posts/sF5gAxnmifQe2TBNt/the-worthlessness-of-vitamin-d-is-mildly-exaggerated --- Narrated by TYPE III AUDIO. ---Images from the article:Apple Podcasts and Spotify do not show images in the episode description. Try Pocket Casts, or another podcast app.