The worthlessness of Vitamin D is mildly exaggerated
5 hours ago
- #randomized trials
- #vitamin D
- #health supplements
- Vitamin D is not a miracle cure but may still offer modest benefits for those with low levels, despite skepticism from randomized trials.
- Early beliefs in vitamin D's magic were debunked by RCTs showing correlations with health outcomes are largely non-causal, but biological complexity suggests plausible local effects.
- Classical view: vitamin D regulates calcium absorption for bones; severe deficiency (<25 nmol/L) causes issues like rickets, but most people have adequate levels.
- Beyond bones, vitamin D acts as a signaling molecule with receptors in many cells, influencing immune function, insulin secretion, and inflammation, though mechanisms are unclear.
- Major RCTs (WHI, VITAL, D-Health) found no dramatic benefits, with small hazard ratios around 0.96 for all-cause mortality, but trials often enrolled people with already high baseline levels.
- Evolutionary evidence suggests humans adapted to higher vitamin D levels (e.g., pale skin for synthesis), supporting a prior that moderate levels (e.g., 80 nmol/L) are likely beneficial.
- Daily dosing may be safer and more effective than bolus doses, which could upregulate counterproductive enzymes and lead to worse outcomes in some trials.
- Weak evidence from meta-analyses hints at small reductions in cancer and all-cause mortality, but detecting these effects requires impractically large trials.
- Vitamin D fortification in foods is common in many countries, complicating trials and suggesting many people already supplement indirectly.
- Given low cost and plausible benefits, supplementing vitamin D for low levels is a reasonable bet, despite uncertain evidence.