Nutritional supplements that may be helpful: 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.12 However, most research shows that while vitamin A supplementation
helps people prevent or treat infections in developing countries where deficiencies are
common,13 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.14 15 16 17
18 19 20 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.21 A double-blind trial for vitamin A supplementation in
Tanzanian children with pneumonia confirmed its lack of effectiveness for this
condition.22 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 infections23 or, in the case of the
common cold, reduce the severity and duration of an infection.24 Most studies
on the common cold used 1 to 4 grams of vitamin C per day.
Lactobacillus acidophilus (the friendly
bacteria found in yogurt) produces acids that kill
invading bacteria.25 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.26
Marginal deficiencies of zinc result in impairments of immune function.27 Supplementation with
50 mg of zinc three times per day for 30 days has been shown to increase immune function in
healthy people.28 However, such large amounts of zinc can potentially cause adverse
effects. 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. Zinc has not been studied as prevention or
treatment for other types of infection.
A multiple vitamin-mineral formula helped elderly
people avoid infections in one double blind trial, but not in another.29
30 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.31 These results suggest that trace minerals may be the most important
micronutrients for preventing infections in the elderly.
Premature infants with very low birth weight have an increased susceptibility to
infections. In a double-blind trial, premature infants were given either selenium supplements (5–7 mcg per 2.2 pounds of body weight)
or placebo. Those receiving the selenium supplements had fewer hospital-acquired
infections.32
Athletes who undergo intensive training
or participate in endurance races (such as a marathon) are at increased risk of developing
infections. In a double-blind study, marathon runners received either glutamine (5 grams immediately after the race and 5 grams again
two hours later) or a placebo. Compared with the placebo, supplementation with L-glutamine
reduced the incidence of infections over the next seven days by 62%.33
Are there any side effects or interactions? Refer to the individual supplement for
information about any side effects or interactions.
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