Colds and flu

Limited evidence

• Vitamin C

  A vitamin found in citrus fruit, peppers, strawberries, blackcurrants, broccoli and potatoes; supplements come as ascorbic acid or ascorbates.

  • NHS: Little evidence that it means fewer colds or a quicker recovery.
  • NICE: The available evidence does not back high doses of vitamin or mineral supplements for colds.

  Also covered by NHS and NIH ODS.

• Zinc

  A mineral found in meat, shellfish, cheese, bread and wheatgerm; sold as tablets, capsules and lozenges.

  • NIH ODS: More research is needed on the best dose, form and timing of zinc for colds.

  Also covered by NICE and NHS.

• Echinacea

  The purple coneflower, a North American plant; its roots and upper parts are made into tablets, capsules and drops.

  • NHS: Little evidence that it means fewer colds or a quicker recovery.
  • NCCIH: Still unclear whether it shortens colds; more research is needed.

  Also covered by NIH ODS.

• Elderberry

  The dark purple berry of the European or black elder tree, sold as syrups, gummies and capsules.

  • NCCIH: Only a small number of studies on colds and flu, with preliminary findings.
  • NIH ODS: It does not appear to make catching a cold less likely.

• Garlic

  The bulb used in cooking, sold as dried powder, oil or aged extract in tablets and capsules.

  • NCCIH: Very little research on colds and flu: two small studies, both with weaknesses.
  • NIH ODS: Only a few studies, and it is not clear whether it makes a difference.

  Also covered by NHS.

• Multivitamins

  One tablet, capsule or gummy with several vitamins and minerals together.

  • NIH ODS: Without a deficiency, extra vitamins and minerals usually make no difference to infections or recovery.

  Also covered by NICE.

No good evidence

• Vitamin D

  A vitamin the body makes when skin is in sunlight. Oily fish, eggs and fortified foods have some; supplements come as D3 or D2.

  • SACN: No effect on respiratory infections was seen in people aged 16 and over.
  • NHS: Everyone should consider 10 micrograms a day in autumn and winter.

  Also covered by NIH ODS.

Things to check

• NHS: See a GP if you have a high temperature for more than 3 days, or cold symptoms do not get better after 10 days.
• NHS: More than 1,000mg of vitamin C a day can cause stomach pain, diarrhoea and flatulence.
• NHS: Do not take more than 25mg of zinc a day in supplements unless a doctor advises it; high doses reduce copper absorption.
• NHS: Do not take more than 100 micrograms (4,000 IU) of vitamin D a day.
• NCCIH: Some people have allergic reactions to echinacea, which may be severe.
• NCCIH: Raw or unripe elderberries, and the leaves and stems of the elder tree, can cause vomiting and severe diarrhoea.
• NCCIH: Garlic supplements may raise the risk of bleeding: tell your doctor, especially before surgery or if you take blood thinners.
• NHS: Herbal medicines are not recommended for children; check with a pharmacist first if you already take any other medicine.

If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.