Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Double-blind trials have shown that common cold symptoms improve^1,2 and recovery is faster³ when andrographis extract containing 48 to 60 mg andrographolides is taken in three or four divided doses daily, beginning as soon as possible after symptoms appear. In addition, preliminary research in Russia suggests andrographis extract may be effective for the treatment of influenza.⁴ This extract was also tested for preventing colds in a double-blind study of teenagers.⁵ After three months, the group taking 5 mg of andrographolides twice daily had only half the number of colds experienced by the placebo group.

Other preliminary⁶ and double-blind^7,8 research has shown similar benefits for treating the common cold from a combination of andrographis extract and an eleuthero extract containing 2.0 to 2.4 mg per day eleutherosides.

Nutrients useful for maintaining healthy immune function are also applicable for preventing infections. Vitamin A plays an important role in immune system function and helps mucous membranes, including those in the lungs, resist invasion by microorganisms.⁹ However, most research shows that while vitamin A supplementation helps people prevent or treat infections in developing countries where deficiencies are common,¹⁰ little to no positive effect, and even slight adverse effects, have resulted from giving vitamin A supplements to people in countries where most people consume adequate amounts of vitamin A.^{11,12,13,14,15,16,17} Moreover, vitamin A supplementation during infections appears beneficial only in certain diseases. An analysis of trials revealed that vitamin A reduces mortality from measles and diarrhea, but not from pneumonia, in children living in developing countries.¹⁸ A double-blind trial for vitamin A supplementation in Tanzanian children with pneumonia confirmed its lack of effectiveness for this condition.¹⁹ In general, parents in the developed world should not give vitamin A supplements to children unless there is a reason to believe vitamin A deficiency is likely, such as the presence of a condition causing malabsorption (e.g., celiac disease). However, the American Academy of Pediatrics recommends that all children with measles should be given high-dose vitamin A for several days.

Vitamin C has antiviral activity, and may help prevent viral infections²⁰ or, in the case of the common cold, reduce the severity and duration of an infection.²¹ Most studies on the common cold used 1 to 4 grams of vitamin C per day.

In general, human studies have found that echinacea taken orally stimulates the function of a variety of immune cells, particularly natural killer cells.²²

A multiple vitamin-mineral formula helped elderly people avoid infections in one double-blind trial, but not in another.^23,24 In a double-blind study of middle-aged and elderly diabetics, supplementation with a multiple vitamin and mineral preparation for one year reduced the risk of infection by more than 80%, compared with a placebo.²⁵ In another double-blind trial, supplements of 100 mcg per day of selenium and 20 mg per day of zinc, with or without additional vitamin C, vitamin E, and beta-carotene, reduced infections in elderly people, though vitamins without minerals had no effect.²⁶ That study suggests that trace minerals may be the most important components of a multiple vitamin and mineral formula for preventing infections.

Lactobacillus acidophilus (the friendly bacteria found in yogurt) produces acids that kill invading bacteria.²⁷ The effective amount of acidophilus depends on the strain used, as well as the concentration of viable organisms. These and other friendly bacteria known as probiotics inhibit the growth of potentially infectious organisms (pathogens) by producing acids, hydrogen peroxide, and natural antibiotics called bacteriocins and microcins, by utilizing nutrients needed by pathogens, by occupying attachment sites on the gut wall that would otherwise be available to pathogens, and by stimulating immune attacks on pathogens. Infections that have been successfully prevented or treated with friendly bacteria include infectious diarrhea, vaginitis, and urinary tract infections.^28,29

Most,^30,31 but not all,³² double-blind studies have shown that elderly people have better immune function and reduced infection rates when taking a multiple vitamin-mineral formula. In one double-blind trial, supplements of 100 mcg per day of selenium and 20 mg per day of zinc, with or without additional vitamin C, vitamin E, and beta-carotene, reduced infections in elderly people, though vitamins without minerals had no effect.³³ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.³⁴ These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Marginal deficiencies of zinc result in immune function impairments.³⁵ In a double-blind study of healthy elderly people, supplementing with 45 mg of zinc per day for one year significantly reduced the frequency of infections.³⁶ Some doctors recommend lower amounts of supplemental zinc for people experiencing recurrent infections, such as 25 mg per day for adults and even lower amounts for children (depending on body weight). Zinc lozenges have been found helpful in some studies for the common cold. Long-term zinc supplementation should in most cases be accompanied by a copper supplement in order to prevent zinc-induced copper deficiency.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.³⁷

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.³⁸

Herbs that support a person’s immune system in the fight against microbes and directly attack microbes include the following: barberry, echinacea, elderberry, goldenseal, licorice, Oregon grape, osha, and wild indigo.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes and directly attack microbes include the following: barberry, echinacea, elderberry, goldenseal, licorice, Oregon grape, osha, and wild indigo.^39,40

Double-blind trials have shown that common cold symptoms improve^41,42 and recovery is faster⁴³ when andrographis extract containing 48 to 60 mg andrographolides is taken in three or four divided doses daily, beginning as soon as possible after symptoms appear. In addition, preliminary research in Russia suggests andrographis extract may be effective for the treatment of influenza.⁴⁴ This extract was also tested for preventing colds in a double-blind study of teenagers.⁴⁵ After three months, the group taking 5 mg of andrographolides twice daily had only half the number of colds experienced by the placebo group.

Other preliminary⁴⁶ and double-blind^47,48 research has shown similar benefits for treating the common cold from a combination of andrographis extract and an eleuthero extract containing 2.0 to 2.4 mg per day eleutherosides.

Caution: Do not use eucalyptus oil internally without supervision by a healthcare professional. As little as 3.5 ml of the oil taken internally has proven fatal.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes and directly attack microbes include the following: barberry, echinacea, elderberry, goldenseal, licorice, Oregon grape, osha, and wild indigo.⁴⁹

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.⁵⁰

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes and directly attack microbes include the following: barberry, echinacea, elderberry, goldenseal, licorice, Oregon grape, osha, and wild indigo.

Herbs that support a person’s immune system in the fight against microbes and directly attack microbes include the following: barberry, echinacea, elderberry, goldenseal, licorice, Oregon grape, osha, and wild indigo.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Herbs that support a person’s immune system in the fight against microbes include the following: American ginseng, andrographis, Asian ginseng, astragalus, coriolus, eleuthero, ligustrum, maitake, picrorhiza, reishi, schisandra, and shiitake.

Caution: It is likely that there are many drug interactions with St. John's wort that have not yet been identified. St. John's wort stimulates a drug-metabolizing enzyme (cytochrome P450 3A4) that metabolizes at least 50% of the drugs on the market.⁵¹ Therefore, it could potentially cause a number of drug interactions that have not yet been reported. People taking any medication should consult with a doctor or pharmacist before taking St. John's wort.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, garlic, green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.⁵²

Herbs that support a person’s immune system in the fight against microbes and directly attack microbes include the following: barberry, echinacea, elderberry, goldenseal, licorice, Oregon grape, osha, and wild indigo.⁵³