Most,^5,6 but not all,⁷ 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.⁸ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.⁹ These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Caution: Synthetic beta-carotene has been linked to increased risk of lung cancer in smokers. Until more is known, smokers should avoid all beta-carotene supplements.

Most,^13,14 but not all,¹⁵ 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.¹⁶ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.¹⁷ These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Beta-carotene and other carotenoids have increased immune cell numbers and activity in animal and human research, an effect that appears to be separate from their role as precursors to vitamin A.^18,19 Placebo-controlled research has shown positive benefits of beta-carotene supplements in increasing numbers of some white blood cells and enhancing cancer-fighting immune functions in healthy people at 25,000–100,000 IU per day.^20,21

In double-blind trials in the elderly, supplementation with 40,000–150,000 IU per day of beta-carotene has increased natural killer (NK) cell activity,²² but not several other measures of immunity.²³

Controlled research has found that 50,000 IU per day of beta-carotene boosted immunity in people with colon cancer but in not those with precancerous conditions in the colon.²⁴ Beta-carotene has also prevented immune suppression from ultraviolet light exposure.²⁵ Effects on immunodefiency in HIV-positive people have been inconsistent using beta-carotene.^26,27

Most,^37,38 but not all,³⁹ 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.⁴⁰ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.⁴¹ These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Vitamin A plays an important role in immune system function and helps mucous membranes, including those in the lungs, resist invasion by microorganisms.⁵¹ However, most research shows that while vitamin A supplementation helps people prevent or treat infections in developing countries where deficiencies are common,⁵² 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.^{53,54,55,56,57,58,59} 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.⁶⁰ A double-blind trial of vitamin A supplementation in Tanzanian children with pneumonia confirmed its lack of effectiveness for this condition.⁶¹ 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 be given short-term supplementation with high-dose vitamin A in cases of hospitalization, malnutrition, and other special circumstances determined by a doctor.⁶²

A combination of antioxidants vitamin A, vitamin C, and vitamin E significantly improved immune cell number and activity compared with placebo in a group of hospitalized elderly people.⁶³ Daily intake of a 1,000 mg vitamin C plus 200 IU vitamin E for four months improved several measures of immune function in a preliminary study.⁶⁴ To what extent immune-boosting combinations of antioxidants actually reduce the risk of infection remains unknown.

Most,^65,66 but not all,⁶⁷ 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.⁶⁸ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.⁶⁹ These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Vitamin C stimulates the immune system by both elevating interferon levels⁷⁰ and enhancing the activity of certain immune cells.^71,72 Two studies came to opposite conclusions about the ability of vitamin C to improve immune function in the elderly,^73,74 and two other studies did not agree on whether vitamin C could protect people from hepatitis.^75,76 However, a review of 20 double-blind studies concluded that while several grams of vitamin C per day has only a small effect in preventing colds, when taken at the onset of a cold, it does significantly reduce the duration of a cold.⁷⁷ In controlled reports studying people doing heavy exercise, cold frequency was reduced an average of 50% with vitamin C supplements ranging from 600 to 1,000 mg per day.⁷⁸ Thus, the overall effect of vitamin C on immune function is unclear, and its usefulness may vary according to the situation.

A combination of antioxidants vitamin A, vitamin C, and vitamin E significantly improved immune cell number and activity compared with placebo in a group of hospitalized elderly people.⁷⁹ Daily intake of a 1,000 mg vitamin C plus 200 IU vitamin E for four months improved several measures of immune function in a preliminary study.⁸⁰ To what extent immune-boosting combinations of antioxidants actually reduce the risk of infection remains unknown.

Animal and test tube studies show noni to have some immune-enhancing activity. Specifically, the polysaccharide component has been shown to increase the release of immune-enhancing compounds that activate white blood cells to destroy tumor cells.¹⁰⁵ The usual recommendation is 4 ounces of noni juice 30 minutes before breakfast (effectiveness is thought to be best on an empty stomach). Human studies are needed to confirm the usefulness of noni.

A double-blind trial showed that 45 grams per day of whey protein increased blood glutathione levels in a group of HIV-infected people.¹⁰⁷ Test tube^108,109 and animal¹¹⁰ studies suggest that whey protein may improve some aspects of immune function.

Most,^111,112 but not all,¹¹³ 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.¹¹⁴ Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.¹¹⁵ These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.

Zinc supplements have been reported to increase immune function.^116,117 This effect may be especially important in the elderly according to double-blind studies.^118,114 Some doctors recommend zinc supplements for people with recurrent infections, suggesting 25 mg per day for adults and lower amounts for children (depending on body weight). However, too much zinc (300 mg per day) has been reported to impair immune function.¹²⁰

While zinc lozenges have been shown to be effective for reducing the symptoms and duration of the common cold in some controlled studies, it is not clear whether this effect is due to an enhancement of immune function or to the direct effect of zinc on the viruses themselves.¹²¹