Vitamins that may be helpful
Most,31 32 but not all,33 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.34 Burn victims have also experienced fewer infections after receiving trace mineral supplements in double-blind research.35 These studies suggest that trace minerals may be the most important micronutrients for enhancing immunity and preventing infections in the elderly.
Vitamin E enhances some measures of immune-cell activity in the elderly.36 This effect is more pronounced with 200 IU per day compared with either lower (60 IU per day) or higher (800 IU per day) amounts, according to double-blind research.37 Intakes under 200 IU per day have not boosted immune function in some reports.38
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.39 40 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.41 42
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,43 but not several other measures of immunity.44
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.45 Beta-carotene has also prevented immune suppression from ultraviolet light exposure.46 Effects on immunodefiency in HIV-positive people have been inconsistent using beta-carotene.47 48
Vitamin C stimulates the immune system by both elevating interferon levels49 and enhancing the activity of certain immune cells.50 51 Two studies came to opposite conclusions about the ability of vitamin C to improve immune function in the elderly,52 53 and two other studies did not agree on whether vitamin C could protect people from hepatitis.54 55 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.56 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.57 Thus, the overall effect of vitamin C on immune function is unclear, and its usefulness may vary according to the situation.
Vitamin A plays an important role in immune system function and helps mucous membranes, including those in the lungs, resist invasion by microorganisms.58 However, most research shows that while vitamin A supplementation helps people prevent or treat infections in developing countries where deficiencies are common,59 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.60 61 62 63 64 65 66 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.67 A double-blind trial of vitamin A supplementation in Tanzanian children with pneumonia confirmed its lack of effectiveness for this condition.68 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.69
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.70 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.71 To what extent immune-boosting combinations of antioxidants actually reduce the risk of infection remains unknown.
The amino acid glutamine is important for immune system function. Liquid diets high in glutamine have been reported in controlled studies to be more helpful to critically ill people than other diets.72 73 Endurance athletes are susceptible to upper respiratory tract infections after heavy exercise, which depletes glutamine levels in blood.74 Although the effects of glutamine supplementation on immune function after exercise have been inconsistent,75 76 a double-blind study giving athletes glutamine (2.5 grams after exercise and again two hours later) reported significantly fewer infections with glutamine.77
Supplements of probiotics (friendly bacteria) such as Lactobacillus acidophilus, or the growth factors that encourage their development in the gastrointestinal tract may help protect the body from harmful organisms in the intestine that cause local or systemic infection according to published research,78 79 including controlled80 trials. The effective amount of probiotics depends on the strain used, as well as the number of viable organisms. Infectious diarrhea in children has been successfully reduced with supplements of friendly bacteria in several trials, some of which were double-blind.81 82
The thymus gland is responsible for many immune system functions. Preliminary studies suggest that a thymus extract known as Thymomodulin® may improve immune function, and double-blind trials in children and adults with a history of recurrent respiratory-tract infections have found reduced numbers of recurrent infections with Thymomodulin supplementation.83 84 85 86 87 Thymomodulin has also been shown in a double-blind study to improve immune function in cases of exercise-induced immune suppression, and in preliminary studies to improve immune function in people with diabetes and in elderly people.88 89 90 91
Zinc supplements have been reported to increase immune function.92 93 This effect may be especially important in the elderly according to double-blind studies.94 95 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.96
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.97
Large amounts of the carotenoid lycopene have been shown to increase the activity of NK cells in the elderly. In a controlled trial, 15 mg of lycopene significantly increased NK cell concentration, but no other immune functions.98
A deficiency of vitamin B12 has been associated with decreased immune function. In a controlled trial, people with vitamin B12 deficiency anemia were also found to have markedly decreased levels of white blood cells associated with immune function.99 Restoration of vitamin B12 stores by means of injections improved levels of these immune cells, suggesting an important role for vitamin B12 in immune function.
Beta-glucan is a fiber-type polysaccharide (complex sugar) derived from the cell wall of baker’s yeast, oat and barley fiber, and many medicinal mushrooms, such as maitake. Numerous experimental studies in test tubes and animals have shown beta-glucan to activate white blood cells.100 101 102 103 104 In fact, there have been hundreds of research papers on beta-glucan since the 1960s.105 The research indicates that beta-1,3-glucan, in particular, is very effective at activating white blood cells known as macrophages and neutrophils. A beta-glucan–activated macrophage or neutrophil can recognize and kill tumor cells, remove cellular debris resulting from oxidative damage, speed up recovery of damaged tissue, and further activate other components of the immune system.106 107 Although the research in test tube and animal studies is promising, many questions remain about the effectiveness of beta-glucan as an oral supplement to enhance immune function in humans. Controlled trials are necessary to determine whether humans can benefit from beta-glucan, and in what amounts oral beta-glucan must be taken from meaningful effects.
The hormone DHEA effects immunity. In a controlled trial, a group of elderly men with low DHEA levels who were given a high level of DHEA (50 mg per day) for 20 weeks, experienced a significant activation of immune function.108 Postmenopausal women have also shown increased immune functioning in just three weeks when given DHEA in double-blind research.109
The effects of eating fish and other dietary sources of omega-3 fatty acids is discussed above in the nutritional section. In terms of fish oil supplements, except for effects in hospitalized patients, most studies have reported that additional omega-3 intake decreases immune function.110 111 112 113 Antioxidants may correct this problem, according to preliminary research.114
Liquid diets containing supplemental arginine, omega-3 fatty acids, and nucleotides such as ribonucleic acid (RNA) have been more effective than other liquid diets in both maintaining immune function and reducing infections in critically ill and post-surgical hospital patients in most,115 116 117 118 119 but not all,120 121 double-blind trials. Typical daily intakes in these trials are 3.3 grams of omega 3 fatty acids, 12.5 grams of arginine, and 1.2 grams of RNA. No research has studied the effects of these supplements in people with less severe health problems.
A double-blind trial showed that 45 grams per day of whey protein increased blood glutathione levels in a group of HIV-infected people.122 Test tube123 124 and animal125 studies suggest that whey protein may improve some aspects of immune function.
Are there any side effects or interactions?
Refer to the individual supplement for information about any side effects or interactions.
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