Are antioxidant supplements useful?

Antioxidant supplements are not a single category: whether they are useful depends strongly on which supplement, for which condition, and in whom. Simply 'taking antioxidants' has no proven general health benefit.

Curcumin has the most positive indications. Fifteen clinical studies show promising results for cognitive decline and muscle loss in older age. When curcumin is combined with piperine (a compound from black pepper that substantially increases absorption), there are also favourable signals for blood sugar, blood lipids and inflammatory markers in diabetes and obesity. Nevertheless, well-designed large-scale studies are still lacking, and the optimal dose is not known.

Vitamins C and E together appear to substantially reduce pain in women with endometriosis: chronic pelvic pain, menstrual pain and pain during sex decreased significantly in an analysis of five RCTs. Note that the study groups were small. A broader analysis of antioxidants in endometriosis showed, however, that studies with the lowest risk of measurement error no longer demonstrated a significant benefit. The evidence is therefore mixed.

CoQ10 is a popular supplement, but formulation problems (it is poorly absorbed) limit its effectiveness. Its efficacy in chronic disease is not yet solidly supported. For cognitive problems and dementia, some supplements show positive signals while others have barely any effect; interactions with medications are also a real point of concern.

Garlic supplements modestly lower blood pressure in people with mild hypertension. They are not a replacement for antihypertensive medication. For hair loss, there are some indications that antioxidant plant compounds may help with damage caused by air pollution or UV radiation, but the evidence is thin and the study's author had financial ties to supplement companies.