Applied Nutrition Zinc

Zinc· evidence: Moderate

Zinc is a trace mineral needed for the immune system, skin, wound healing and many enzymes. Men need about 9.5 mg a day and women 7 mg in the UK, mostly from meat, shellfish, dairy, bread and cereals. Vegans and vegetarians can fall short because plant foods contain phytates that reduce absorption.

Supplements help people whose intake is low. Zinc lozenges taken at the very start of a cold have been studied with mixed results; tablets swallowed every day by well-fed people are not shown to add much.

Long-term high doses cause problems, mainly by blocking copper absorption, so more is not better.

Typical dose: Adults need about 7 mg (women) to 9.5 mg (men) a day from all sources (NRV on labels: 10 mg). Supplements usually give 5 to 25 mg.

Safety: The NHS advises not taking more than 25 mg of zinc a day from supplements unless a doctor advises it. Long-term high doses can cause copper deficiency, anaemia and weakened immunity. Zinc can upset the stomach if taken without food, and it reduces absorption of some antibiotics.

Research we looked at:
NHS. Others: vitamins and minerals (zinc). nhs.uk/conditions/vitamins-and-minerals/others
EFSA NDA Panel. Scientific opinion on dietary reference values for zinc. EFSA Journal 2014;12(10):3844.
Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open 2017;8(5):2054270417694291.

Vitamin C· evidence: Moderate

Vitamin C (ascorbic acid, or mineral ascorbates such as sodium, calcium or magnesium ascorbate) is an essential vitamin found in fruit and vegetables. Adults need about 40 mg a day in the UK, and most people who eat fruit and vegetables get enough. The body cannot store much, and absorption falls off at higher doses, so the extra from a 1,000 mg tablet is largely passed in urine.

The best evidence on colds (a Cochrane review) found that taking vitamin C every day does not stop most people catching colds, but may shorten them slightly. People doing very heavy physical exercise are the exception, where regular vitamin C roughly halved the number of colds in trials.

A supplement makes sense if your diet is low in fruit and vegetables, if you smoke, or around periods of hard training. Most people do not need mega-doses, and fancy forms (liposomal, ester or buffered) have little evidence of meaningful benefit over plain ascorbic acid, though buffered forms can be gentler on the stomach.

Typical dose: The UK reference intake for adults is 40 mg a day (NRV on labels: 80 mg). Supplements commonly give 200 to 1,000 mg.

Safety: The FSA advises that 1,000 mg (1 g) a day or less from supplements is unlikely to cause harm. Higher doses can cause stomach pain, diarrhoea and wind. People with a history of kidney stones, haemochromatosis (iron overload) or kidney disease should speak to their GP before taking high doses. Chewable and powder forms are acidic and can affect tooth enamel.

Research we looked at:
NHS. Vitamin C. nhs.uk/conditions/vitamins-and-minerals/vitamin-c
Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 2013;(1):CD000980.
EFSA NDA Panel. Scientific opinion on dietary reference values for vitamin C. EFSA Journal 2013;11(11):3418.
Carr AC, Vissers MCM. Synthetic or food-derived vitamin C: are they equally bioavailable? Nutrients 2013;5(11):4284-4304.

Cost per daily dose lets you compare packs of different sizes fairly.Worked out from our current prices.