Sacn

Dietary supplements are beneficial in specific, defined contexts: correcting deficiencies (vitamin D, B12, folate, iron), supporting life stages with increased needs (pregnancy, older adults), and supplementing macronutrients when food intake is insufficient. This article covers where supplements have genuine evidence and where claims exceed the evidence.

Vitamin supplementation is not universally necessary for people eating a varied diet. UK-specific evidence-based indications: vitamin D (10 mcg/day for all UK adults — SACN 2016), folic acid (400 mcg/day before and during early pregnancy — NICE), vitamin B12 (vegans and strict vegetarians), iron (only if deficiency confirmed by blood test). A SACN review concluded there is no consistent evidence that multivitamins benefit well-nourished UK adults.

UK RNI for vitamin C: 40 mg/day (SACN); most UK adults achieve this through diet. EFSA-authorised claims: immune function, collagen synthesis, iron absorption enhancement, protection from oxidative stress. Megadose vitamin C supplementation (1,000 mg+) has no RCT evidence for preventing colds in the general population (Hemilä 2013 Cochrane review). Smokers have genuinely higher needs (~80 mg/day). Food sources provide vitamin C with additional phytonutrients that supplements cannot replicate.

UK evidence-based supplements for vegetarians: B12 is essential for vegans and recommended for low-dairy vegetarians (SACN); vitamin D 10 mcg/day for all UK adults regardless of diet (SACN 2016); iodine 150 mcg/day for those limiting dairy (SACN 2014); omega-3 as algal oil (EPA+DHA) if not eating oily fish. Iron: test first — do not supplement without confirmed deficiency. Lacto-ovo vegetarians eating dairy and eggs regularly have fewer critical gaps.

Food is superior to supplements for most vitamins and minerals due to bioavailability advantages, synergistic nutrient interactions, and the food matrix effect. Supplementation is specifically indicated for vitamin D (UK adults year-round), folate (pre-pregnancy), B12 (vegans), and iron (confirmed deficiency). This article explains the evidence for each approach.