The worthlessness of vitamin D is mildly exaggerated
11 hours ago
- Vitamin D was once thought to be a miracle cure for many conditions, but large randomized trials show it is not a miracle.
- The classical view holds vitamin D as a bone vitamin that regulates calcium absorption; severe deficiency causes rickets.
- Correlation studies linked higher vitamin D levels to better health outcomes, but these may be due to confounding and reverse causation.
- Large RCTs (WHI, VITAL, D-Health) found no significant benefit for all-cause mortality and only weak evidence for some outcomes.
- Daily dosing may be more effective than bolus (monthly) dosing, possibly avoiding harmful metabolic fluctuations.
- Biology and evolution suggest that moderate vitamin D levels (e.g., 80 nmol/L) are likely better than low levels (e.g., 40 nmol/L) and unlikely harmful.
- Meta-analyses show hazard ratios slightly below 1 for all-cause and cancer mortality with daily dosing, close to statistical significance.
- Most trials enrolled people with already moderate vitamin D levels, making modest effects hard to detect; people with low baseline levels might benefit more.
- Fortification of foods is common in many countries, indicating widespread acceptance of vitamin D’s importance.
- The author concludes that for people with low vitamin D levels, supplementing is a wise choice given weak but positive evidence and low cost.