Review of 84 Studies Finds Most Supplements Offer Little Benefit as Timing Shapes Absorption
Updated
Updated · The Conversation · Aug 20
Review of 84 Studies Finds Most Supplements Offer Little Benefit as Timing Shapes Absorption
3 articles · Updated · The Conversation · Aug 20
Summary
A review of 84 studies found routine vitamin and mineral supplements gave generally healthy adults little or no protection against cardiovascular disease, cancer or early death, while unnecessary high doses can cause harms including B6-linked nerve damage and vitamin A toxicity.
Iron showed the clearest timing effects: coffee cut absorption of a 100mg supplement by 54% in a small study, breakfast cut it by 66%, and NHS advice is to take ferrous sulfate 30 minutes before food or two hours after if tolerated.
Vitamin D is better absorbed with a fat-containing meal, supporting use with a main meal, but medicines such as orlistat and corticosteroids can interfere in ways that changing the hour may not fix.
Vitamin B12 timing matters less than the reason for treatment: vegans who did not supplement had poorer B12 status, while metformin and acid-suppressing drugs can lower absorption or levels over time.
The broader message is to take supplements only for evidence-based reasons—such as diagnosed deficiency, folic acid in early pregnancy, B12 need or 10 micrograms of vitamin D in UK autumn and winter—and to check labels, overlap and drug interactions.