For a general overview, see our consumer fact sheet. Interest in dietary supplement ingredients that might enhance immune function and reduce the risk of infectious diseases is high, especially after the emergence of COVID The immune system defends the body from pathogens that cause disease and is comprised of innate responses, which are the first line of defense, and adaptive responses, which become engaged later [ ].

The innate immune system includes physical barriers, such as the skin and gut epithelium, that help prevent pathogen entry. It also includes leukocytes white blood cells —such as neutrophils, macrophages which release cytokines , and natural killer cells—that attempt to find and eliminate foreign pathogens.

However, these components are nonspecific, meaning that unlike the adaptive immune system, they do not recognize and respond to specific pathogens [ 1 , 2 , 4 ]. The adaptive immune system consists of B lymphocytes B cells that secrete antibodies a process known as humoral immunity and T lymphocytes, which are also known as T cells a process known as cell-mediated immunity , both of which are pathogen specific [ ].

The adaptive response takes several days or weeks to develop, but it generates immunological memory; as a result, a subsequent exposure to the same pathogen leads to a vigorous and rapid immune response [ 1 , 3 , 5 ].

Vaccinations stimulate the adaptive immune system, protecting the body from future exposures [ 2 ]. Inflammation helps eliminate the pathogen and initiate the healing process, but it can also cause symptoms and severe pathologies [ 6 , 7 ]. For example, activation of CD8 T cells as part of the adaptive immune response can increase inflammation and cause pulmonary damage.

This process can lead to acute respiratory distress syndrome ARDS , which has occurred in some patients with COVID [ 7 ]. Consuming adequate amounts of several vitamins and minerals—including vitamin A, vitamin C, vitamin D, vitamin E, selenium, and zinc—is important for proper immune function, and clinical deficiencies of these nutrients weaken immunity and can increase susceptibility to infections [ 2 , 4 , 5 , ].

Other ingredients whether provided through foods or dietary supplements , such as botanicals and probiotics, are not essential in the body but might affect immune function. Measuring the impact of dietary supplement ingredients, such as vitamins, minerals, or other substances, on the immune system is difficult because the immune system is a complex network of organs, tissues, and cells [ 11 , 12 ].

No single, straightforward measure of immune system function and resistance to disease exists. Indirectly, immune function can be assessed by examining a person's risk and severity of infectious diseases. This fact sheet summarizes the effects of various dietary supplement ingredients on immune function and the risk of selected infectious diseases, including the common cold, influenza and other respiratory tract infections, infectious diarrhea, and HIV infection.

These diseases can be caused by numerous pathogens. For example, the common cold is caused by a wide variety of respiratory viruses, most commonly rhinovirus, but also coronaviruses, adenoviruses, and other virus serotypes [ 13 ].

Dietary supplement ingredients in each category are presented in alphabetical order. In some cases, cited research involves intravenous, enteral, or parenteral administration. Dietary ingredients administered by these routes are not classified as dietary supplements, but the information is included for completeness.

For information on dietary supplements and COVID, please see the Office of Dietary Supplements ODS health professional fact sheet, Dietary Supplements in the Time of COVID Consuming a nutritious variety of foods helps maintain overall good health and a strong immune system [ 14 ].

Obtaining adequate amounts of vitamins and minerals is also important for good health, and deficiencies of certain vitamins and minerals—including vitamins A, B6, B12, C, D, E, and K; folate; and copper, iodine, iron, magnesium, selenium, and zinc—might adversely affect immune function. The European Society for Clinical Nutrition and Metabolism states that low intakes or status of several micronutrients—including vitamins A, E, B6, and B12; zinc; and selenium—are associated with worse outcomes in patients with viral infections [ 14 ].

If needed, vitamin and mineral supplementation can boost intakes to recommended levels. In the absence of deficiency, however, routine supplementation with micronutrients probably does little to prevent or treat specific infections [ 14 , 28 ].

The following subsections describe research on the effects of dietary supplements containing more commonly studied vitamins and minerals—vitamins A, C, D, and E, selenium, and zinc—on immune function.

Many foods contain vitamin A, an essential nutrient. Two sources of vitamin A are available in the human diet: preformed vitamin A retinol and retinyl esters and provitamin A carotenoids beta-carotene, alpha-carotene, and beta-cryptoxanthin.

Preformed vitamin A is present in foods from animal sources, including dairy products, eggs, fish, and organ meats. Provitamin A carotenoids come from plant foods, including leafy green vegetables, orange and yellow vegetables, tomato products, fruits, and some vegetable oils.

The Recommended Dietary Allowance RDA for vitamin A is to 1, mcg retinol activity equivalents RAE for infants and children, depending on age, and to 1, mcg RAE for adults, including those who are pregnant or lactating [ 29 ].

Vitamin A plays a critical role in vision and growth. It is also required for the formation and maintenance of epithelial tissue and the differentiation, maturation, and function of macrophages and other cells of the innate immune system [ 5 , 15 , 30 ].

Vitamin A deficiency is associated with increased susceptibility to infections, altered immune responses, and impairment in the ability of epithelial tissue to act as a barrier to pathogens [ 5 , 15 , 30 , 31 ].

Although vitamin A deficiency is rare in the United States, it is common in many low- and middle-income countries and is one of the top causes of preventable blindness in children [ ].

It is also associated with an increased risk of respiratory diseases, diarrhea, and measles. For this reason, the World Health Organization WHO and other expert groups recommend universal vitamin A supplementation for children younger than 5 years including those who have HIV in populations with a high risk of vitamin A deficiency [ 33 , 37 ].

Recommended doses in these populations are 30, mcg RAE , International Units [IU] vitamin A once for infants age 6—11 months and 60, mcg RAE , IU every 4—6 months for children age 1—5 years [ 37 ].

The authors of a analysis concluded that vitamin A supplementation has reduced child mortality rates in sub-Saharan Africa, although rates are still substantial in many countries in this region [ 38 ].

Vitamin A deficiency can decrease resistance to pathogens in the mucosa of the digestive tract and increase the risk of diarrhea [ 30 ]. Vitamin A deficiency also increases the risk of mortality from diarrhea in young children [ 39 ]. A analysis of data from 83 countries found that 94, deaths from diarrhea in children were associated with vitamin A deficiency [ 39 ].

For these reasons, researchers have examined the effects of vitamin A supplementation on childhood diarrhea. Results from these studies suggest that vitamin A supplementation reduces the risk and severity of diarrhea in children in low- and middle-income countries but does not appear to benefit very young infants.

A systematic review of studies that examined the effects of vitamin A on childhood diarrhea included 13 clinical trials in a total of 37, participants that examined risk of diarrhea and 7 clinical trials in a total of 90, children age 6 months to 5 years, mostly in low- or middle-income countries, that examined the risk of death from diarrhea [ 40 ].

Vitamin A doses ranged from 6, mcg RAE 20, IU to 61, mcg RAE , IU , depending on age, and were administered in a single dose or in several doses administered weekly or every few months for up to 24 months. In very young infants, however, limited evidence suggests that vitamin A supplementation does not affect diarrhea morbidity or mortality.

A Cochrane Review that examined the effects of vitamin A supplementation in children age 1 to 6 months found that 7, mcg RAE 25, IU to 15, mcg RAE 50, IU vitamin A administered three times during the first few months of life did not reduce the risk of diarrhea or of death due to diarrhea [ 41 ].

However, these findings were based on only two clinical trials that examined the incidence of diarrhea in 5, participants and one trial that examined mortality from diarrhea in participants. It can also increase the risk of comorbidities, including diarrhea and respiratory diseases [ 42 ].

HIV is treated with a combination of medicines called antiretroviral therapy ART , which can reduce the risk of HIV transmission from one individual to another by reducing viral load and help people with HIV live longer [ 44 ]. The results of studies of the effects of vitamin A supplementation on risk of HIV transmission or disease outcomes in children and adults have been mixed.

Two Cochrane Reviews found that vitamin A supplements improved some but not all outcomes examined in children but offered no benefit in adults with HIV infection. A Cochrane Review included three clinical trials in a total of infants and children with HIV age 5 years or younger [ 45 ].

Another Cochrane Review examined the effects of vitamin A supplementation in four clinical trials that included a total of adults with HIV infection mostly women age 18 to 45 [ 46 ]. None of the trials was adequately powered to assess mortality or morbidity outcomes.

Results were negative in another Cochrane Review [ 47 ]. It included five clinical trials conducted in sub-Saharan Africa with a total of 7, pregnant participants with HIV. Vitamin A supplementation did not affect the risk of mother-to-child transmission of HIV.

Largely because of the findings from this analysis, the WHO does not recommend vitamin A supplementation in people with HIV who are pregnant in order to reduce the risk of mother-to-child transmission of HIV [ 48 ]. Most of the findings were also negative in a systematic review of vitamin A supplementation that included 17 clinical trials, conducted mostly in sub-Saharan Africa, in a total of 12, children and adults mostly pregnant women with HIV [ 31 ].

Vitamin A dosing schedules varied widely but commonly included 1, to 3, mcg RAE 5, to 10, IU daily or one-time doses of 15, to , mcg RAE 50, to , IU at baseline or delivery. In addition, it did not affect rates of gastrointestinal and HIV symptoms.

However, in one trial included in the review, vitamin A supplementation , mcg RAE [, IU] at delivery reduced the number of clinic visits for some health conditions in women with HIV postpartum and in another trial, supplementation with 15, to 60, mcg RAE 50, to , IU vitamin A depending on age five times per year reduced rates of diarrhea in children with HIV.

Supplements 1, mcg RAE [5, IU] daily plus 60, mcg RAE [, IU] at delivery also reduced the risk of preterm birth in one study in pregnant women with HIV. Whether maternal vitamin A supplementation affects the morbidity and mortality of breastfed infants was the focus of a cross-sectional study in lactating people with HIV from sub-Saharan Africa [ 49 ].

The study included mothers, of whom took vitamin A supplements after giving birth doses and frequency not reported ; the other did not. Vitamin A supplementation did not affect infant mortality rates or the risk of cough with difficulty breathing, diarrhea, or fever in the breastfed infants.

In , measles was responsible for more than , deaths around the world, mostly in young children in low-income countries [ 50 ]. A major risk factor for severe measles is low vitamin A status [ 5 ]. Research suggests that vitamin A supplementation reduces the risk of measles in children who are at high risk of vitamin A deficiency.

However, whether vitamin A supplementation reduces the risk of death from measles is less clear. However, other studies have found no effect of vitamin A supplementation on risk of death from measles.

A systematic review included six clinical trials in a total of 19, children younger than 5 years that examined the effect of vitamin A supplementation on risk of measles and five clinical trials in a total of 88, children that examined the risk of death from measles.

Most studies were conducted in low- and middle-income countries [ 40 ]. Vitamin A doses ranged from 2, mcg RAE 8, IU to 60, mcg RAE , IU , depending on age, and were administered as single doses or over weeks or months. However, the supplements did not affect risk of death due to measles, according to the results of six clinical trials in a total of 1,, children.

Again, findings were mostly negative in a systematic review of 13 clinical trials conducted in India or sub-Saharan Africa of vitamin A supplementation for measles in a total of 1,, infants and children [ 31 ]. Vitamin A supplementation did not reduce the risk of measles in healthy infants and children or mortality rates in those with measles.

The supplements also had no effect on immunological responses, except for higher levels of immunoglobulin G antibodies in children taking vitamin A in one study.

However, a few trials found that vitamin A supplementation reduced the risk of a few measles-related complications, such as pneumonia, especially among children with vitamin A deficiency, and severe diarrhea.

Vitamin A deficiency is associated with recurrent respiratory tract infections in children [ 33 , 51 ]. However, findings have been mixed from trials of the effects of vitamin A supplementation on the risk and severity of pneumonia and other respiratory tract infections in children [ 33 , 52 ].

In addition, some evidence suggests that doses of vitamin A supplementation that are higher than the WHO recommends might increase the risk of respiratory tract infections among children with normal nutritional status [ 53 ]. Effects were mixed in a meta-analysis of 15 clinical trials in a total of 3, children age not specified that examined the effects of mcg RAE 1, IU to , mcg RAE , IU vitamin A supplementation for several days or weeks on the risk of morbidity and mortality from pneumonia [ 52 ].

Vitamin A supplementation shortened the durations of hospital stays and of signs and symptoms, including fever, cough, and abnormal chest X-rays. However, it did not reduce the risk of death due to pneumonia.

Other clinical trials have found that vitamin A supplements do not reduce the risk of respiratory tract infections or of death from these infections. A Cochrane Review that included 11 clinical trials in a total of 27, children age 6 months to 5 years found that 15, mcg RAE 50, IU to 60, mcg RAE , IU , depending on age, vitamin A supplementation did not significantly affect the risk of lower respiratory tract infections [ 33 ].

In addition, vitamin A supplements did not affect the risk of death due to these infections, according to the results of nine studies in a total of 1,, children that examined this outcome.

A separate Cochrane Review also found that vitamin A supplementation 7, mcg RAE [25, IU] or 15, mcg RAE [50, IU] given three times during the first 14 weeks of life did not reduce the risk of respiratory tract infections or death due to such infections in very young infants age 1 to 6 months, although the review included only one trial for each outcome [ 41 ].

Similarly, a systematic review of 16 clinical trials that combined nine trials in a meta-analysis in a total of 32, children found that vitamin A supplementation did not reduce the risk of respiratory tract infections [ 54 ].

Another meta-analysis found that taking vitamin A supplements to reduce the risk of respiratory tract infections might even be harmful in some circumstances [ 53 ]. The analysis included 26 clinical trials that examined acute or lower respiratory tract infections in a total of 50, children from birth to age 11 years.

Vitamin A doses ranged from 15, mcg RAE 50, IU to , mcg RAE 1,, IU depending on age and were administered as a single dose or over days, weeks, months, or years. Overall, vitamin A supplementation did not affect the risk, severity, or duration of acute or lower respiratory tract infections.

These tolerable upper intake levels ULs, maximum daily intake unlikely to cause adverse health effects , however, do not apply to people taking vitamin A under the care of a physician. Higher intakes can cause severe headache, blurred vision, nausea, dizziness, aching muscles, and coordination problems.

In severe cases, cerebral spinal fluid pressure can increase, leading to drowsiness and, eventually, coma [ 55 ]. Regular consumption of high doses of preformed vitamin A from foods or supplements can cause dry skin, painful muscles and joints, fatigue, depression, and abnormal liver test results.

High intakes of preformed vitamin A can also cause congenital birth defects [ 35 ]. Unlike preformed vitamin A, beta-carotene is not known to be teratogenic or lead to reproductive toxicity.

Therefore, beta-carotene does not have an established UL [ 56 ]. Vitamin A might interact with some medications. For example, orlistat, a weight-loss medication, can decrease the absorption of vitamin A, resulting in low plasma levels in some patients [ 57 ].

In addition, synthetic retinoids derived from vitamin A that are used as oral prescription medicines, such as acitretin used to treat psoriasis, increase the risk of hypervitaminosis A when taken in combination with vitamin A supplements [ 57 ]. More information on vitamin A is available in the ODS health professional fact sheet on vitamin A.

Vitamin C, also called ascorbic acid, is an essential nutrient contained in many fruits and vegetables , including citrus fruits, tomatoes, potatoes, red and green peppers, kiwifruit, broccoli, strawberries, brussels sprouts, and cantaloupe. The RDA for vitamin C is 15 to mg for infants and children, depending on age, and 75 to mg for nonsmoking adults, including those who are pregnant or lactating; people who smoke need 35 mg more per day [ 56 ].

Vitamin C plays an important role in both innate and adaptive immunity, probably because of its antioxidant effects, antimicrobial and antiviral actions, and effects on immune system modulators [ 5 , 32 , ]. Vitamin C helps maintain epithelial integrity, enhance the differentiation and proliferation of B cells and T cells, enhance phagocytosis, normalize cytokine production, and decrease histamine levels [ 4 , 5 , 60 ].

It might also inhibit viral replication [ 13 ]. Vitamin C deficiency impairs immune function and increases susceptibility to infections [ 5 , 58 , 60 ]. People who smoke and those whose diets include a limited variety of foods such as some older adults and people with alcohol or drug use disorders are more likely than others to obtain insufficient amounts of vitamin C [ 61 , 63 ].

In addition, regular consumption of vitamin C might reduce the duration of the common cold and the severity of its symptoms, but taking vitamin C supplements only after symptom onset does not provide consistent benefits [ 5 , 59 ].

Several clinical trials have examined whether vitamin C supplementation reduces the risk of developing the common cold in the general population and those exposed to extreme physical stress. One trial included 92 runners and a control group of 92 nonrunners mostly male, age 25 years or older who took mg per day vitamin C or placebo for 21 days before a kilometer ultramarathon [ 66 ].

Among nonrunners, however, the incidence of upper respiratory tract infections was not different between supplement and placebo users. In addition, the duration of symptoms in nonrunners who took vitamin C was shorter mean 4. A Cochrane Review included 29 clinical trials including the one described above that examined the effects of vitamin C supplementation in 11, participants [ 13 ].

Most trials had participants from the general population, but five trials involved people exposed to extreme physical stress, including marathon runners, skiers, and soldiers in subarctic areas. The authors noted that extreme physical stress generates oxidative stress, and the antioxidant action of vitamin C might help counteract this effect in people exposed to this type of physical stress [ 13 ].

Findings were positive in a systematic review and meta-analysis that included 24 clinical trials in a total of 10, adults [ 67 ]. Daily doses of vitamin C ranged from less than mg to 2, mg for 5 days to 5 years.

Some evidence suggests that vitamin C supplementation might be more effective in people with low vitamin C status [ 64 ]. For example, a clinical trial included 28 healthy, nonsmoking men age 18 to 35 years who took 1, mg vitamin C or placebo daily for 8 weeks during the peak of the cold season, January through April [ 68 ].

Some researchers believe that high-dose intravenous vitamin C which is classified as a drug in the United States might mitigate the damage caused by sepsis, but evidence from clinical trials is mixed, and some evidence suggests that this treatment may cause harm.

Evidence on the potential harms of intravenous vitamin C for sepsis comes from a clinical trial in Canada, France, and New Zealand that included men and women mean age 65 years with an infection who were in the intensive care unit ICU for 24 hours or less and were treated with vasopressor medications [ 69 ].

On day 28, those treated with intravenous vitamin C had a higher risk of death or organ dysfunction than those treated with a placebo. Other trials have had mixed findings.

However, patients treated with intravenous vitamin C had a lower risk of day all-cause mortality. Two systematic reviews and meta-analyses that examined the effects of intravenous vitamin C in critically ill patients also had mixed findings [ 71 , 72 ]. In some studies, intravenous vitamin C was combined with thiamin and hydrocortisone.

Vitamin C infusion did not affect overall mortality risk. The intravenous vitamin C did not affect organ dysfunction, length of ICU stay, or risk of death 90 days to 1 year after study enrollment. These ULs, however, do not apply to people taking vitamin C under the care of a physician.

Higher vitamin C intakes can cause diarrhea, nausea, and abdominal cramps. High intakes might also cause falsely high or low readings on some blood glucose meters that are used to monitor glucose levels in people with diabetes [ ].

In people with hemochromatosis, high doses of vitamin C could exacerbate iron overload and damage body tissues [ 56 , 61 ]. The Food and Nutrition Board of the National Academies of Sciences, Engineering, and Medicine recommends that people with hemochromatosis be cautious about consuming vitamin C doses above the RDA [ 56 ].

Vitamin C supplementation might interact with some medications. For example, it might reduce the effectiveness of radiation therapy and chemotherapy by protecting tumor cells from the action of these agents [ 76 ].

Vitamin C might also enhance the absorption of levothyroxine when taken at the same time [ 77 ]. More information on vitamin C is available in the ODS health professional fact sheet on vitamin C. For information on vitamin C and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Vitamin D exists in two forms: vitamin D2 and vitamin D3.

It is an essential nutrient that is naturally present in only a few foods , such as fatty fish including salmon and tuna and fish liver oils.

In addition, beef liver, cheese, and egg yolks contain small amounts. Fortified foods, especially fortified milk, provide most of the vitamin D in the diets of people in the United States. The RDA for vitamin D is 10 to 15 mcg IU to IU for children, depending on age, and 15 to 20 mcg to IU for adults, including those who are pregnant or lactating [ 78 ].

The body can also synthesize vitamin D as a result of sun exposure. Vitamin D obtained from sun exposure, foods, and supplements is biologically inert until it undergoes two hydroxylations in the body for activation.

The first hydroxylation, which occurs in the liver, converts vitamin D to hydroxyvitamin D [25 OH D]. The second hydroxylation occurs primarily in the kidney and forms the physiologically active 1,dihydroxyvitamin D [1,25 OH 2D].

Serum concentration of 25 OH D is the main indicator of vitamin D status [ 78 ]. However, 25 OH D levels defined as deficient or adequate vary from study to study.

In addition to its well-known effects on calcium absorption and bone health, vitamin D plays a role in immune function [ 5 , 58 , ]. Vitamin D appears to lower viral replication rates, suppress inflammation, and increase levels of T-regulatory cells and their activity [ 16 , 58 , ].

In addition, almost all immune cells e. These capabilities suggest that vitamin D can modulate both innate and adaptive immune responses [ 5 , 16 , , 85 , 87 , 88 ]. It also impairs macrophage function and interleukin production [ 5 ].

Dietary surveys indicate that most people in the United States consume less than recommended amounts of vitamin D [ 90 ]. Nevertheless, according to a — analysis of serum 25 OH D concentrations, most people in the United States age 1 year and older have adequate vitamin D status [ 91 ]. Sun exposure, which increases serum 25 OH D levels, is one of the reasons serum 25 OH D levels are usually higher than would be predicted on the basis of dietary vitamin D intakes alone [ 78 ].

Researchers have investigated whether higher vitamin D status can reduce the risk of seasonal infections, having observed that low vitamin D status due to less sun exposure and higher risk of upper respiratory tract infections are more common in the winter [ 87 , 92 ].

An analysis of data on the association between 25 OH D levels and recent upper respiratory tract infections in 18, participants age 12 years and older from the third National Health and Nutrition Examination Survey — suggests that lower vitamin D levels are associated with a higher risk of respiratory tract infections [ 93 ].

In another analysis, vitamin D insufficiency and deficiency were associated with a higher mortality risk from respiratory diseases than vitamin D sufficiency during 15 years of follow-up in 9, adults age 50—75 years in Germany [ 94 ].

Results from clinicals trials have been mixed but suggest that vitamin D supplementation might modestly reduce the risk of respiratory tract infections. For example, in a clinical trial in Japan, children age 6 to 15 years took 30 mcg 1, IU vitamin D3 or placebo daily during 4 winter months [ 95 ].

In this trial, both groups had adequate mean 25 OH D levels for bone and overall health at baseline. Results have been mixed from systematic reviews and meta-analyses that have examined the effects of vitamin D supplementation on the risk of pneumonia and other respiratory tract infections.

Results were negative in a Cochrane Review that evaluated the use of vitamin D supplementation for preventing infections, including pneumonia, in children younger than 5 years [ 98 ]. The review included two trials that examined pneumonia incidence in a total of 3, participants; one trial was placebo controlled, and the other had a control group that received no treatment.

A systematic review and meta-analysis of vitamin D supplementation to prevent acute respiratory tract infections mostly upper respiratory tract infections had mixed findings.

This analysis included 25 clinical trials and a total of 10, participants from newborns to adults age 95 years [ 99 ]. Study durations ranged from 7 weeks to 1. However, vitamin D supplementation was beneficial only in participants who took supplements daily or weekly, not in those who took one or more bolus doses.

A subsequent systematic review and meta-analysis by the same research team that included 46 clinical trials and a total of 75, participants age 0 to 95 years found some benefits of vitamin D supplementation [ ].

Other systematic reviews and meta-analyses have also found that vitamin D supplementation helps reduce the risk of respiratory tract infections and influenza in children and adults [ ] and that vitamin D deficiency is associated with an increased risk of community-acquired pneumonia in children and adults [ ].

In addition, serum 25 OH D concentrations are inversely associated with risk and severity of acute respiratory tract infections [ ]. In contrast, a meta-analysis of 30 clinical trials in a total of 30, participants age 3 to 81 years found that vitamin D supplementation did not reduce the risk of respiratory tract infections [ ].

Mixed findings were reported in a meta-analysis of six trials in a total of 6, children and seven trials in a total of 3, adults [ 54 ]. Vitamin D supplementation did not reduce the risk of respiratory tract infections in adolescents and adults in two clinical trials whose results were published in [ , ].

In one of these trials, 34, men and women age 18 to 75 years in Norway who were not taking daily vitamin D supplements took 5 mL cod liver oil containing 10 mcg IU vitamin D3 or placebo for up to 6 months during the winter [ ].

The cod liver oil did not reduce the incidence of acute respiratory infections. The other trial involved 6, participants age 16 years or older in the United Kingdom who were not taking vitamin D supplements [ ].

Half of the participants were offered a vitamin D blood test. The other participants were not offered vitamin D tests or supplementation, and the study did not use a placebo.

Neither lower nor higher doses of vitamin D3 reduced the risk of acute respiratory tract infections. Researchers have also examined whether vitamin D supplementation helps treat respiratory tract infections, but results suggest that it has limited, if any, benefits.

A meta-analysis included 18 clinical trials in a total of 3, participants with mean ages between 12 months and 62 years [ ]. It assessed whether one-time, daily, or occasional vitamin D doses ranging from 15 to 15, mcg IU to , IU , depending on dosing schedule, for up to 8 months helped treat respiratory infections.

Treatment outcomes differed among trials but included sputum conversion for pulmonary tuberculosis , survival rate, and no need for ICU admission. Vitamin D supplementation had some small beneficial effects on treatment outcomes, but when the authors analyzed only the 12 high-quality trials, the differences between groups in the trials were no longer statistically significant.

Inflammation and comorbidities from HIV infection may also contribute to low vitamin D levels [ ]. Low vitamin D levels could partly explain why people with HIV appear to have a higher risk of major bone fractures [ ]. Vitamin D deficiency might also increase HIV infection severity [ ].

Observational studies show associations between low vitamin D status and increased risk of pulmonary tuberculosis and mortality in people with HIV [ ]. In addition, low levels of vitamin D in pregnant people with HIV are associated with poor fetal and infant growth [ ]. Results from clinical trials, however, have not shown that vitamin D supplementation improves outcomes in people with HIV [ , ].

Vitamin D3 supplementation did not affect rates of mortality or pulmonary tuberculosis. Moreover, vitamin D3 supplementation did not affect secondary outcomes, including risk of HIV progression, viral suppression, comorbidities nausea, vomiting, cough, fever, or diarrhea , changes in body weight, or depression [ ].

Another clinical trial in Tanzania examined the effects of vitamin D3 supplementation during pregnancy and lactation in 2, people with HIV [ ]. Vitamin D3 supplementation did not affect the risk of maternal HIV progression or death. The results also showed no difference in the risk of small-for-gestational-age birth or of infant stunting at 1 year.

Daily intakes of up to 25— mcg 1, IU—4, IU vitamin D, depending on age, in foods and dietary supplements are safe for infants and children, and up to mcg 4, IU is safe for adults, including those who are pregnant or lactating [ 78 ]. These ULs, however, do not apply to people taking vitamin D under the care of a physician.

Higher intakes usually from supplements can lead to nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones.

In extreme cases, vitamin D toxicity causes renal failure, calcification of soft tissues throughout the body including in coronary vessels and heart valves , cardiac arrhythmias, and even death [ ]. Several types of medications might interact with vitamin D.

For example, orlistat, statins, and steroids can reduce vitamin D levels [ , ]. In addition, taking vitamin D supplements with thiazide diuretics might lead to hypercalcemia [ ].

More information on vitamin D is available in the ODS health professional fact sheet on vitamin D. For information on vitamin D and COVID, please see the ODS health professional fact sheet, Dietary Supplements in the Time of COVID Vitamin E, also called alpha-tocopherol, is an essential nutrient that is present in several foods , including nuts, seeds, vegetable oils, and green leafy vegetables.

The RDA for vitamin E is 4 to 15 mg for infants and children, depending on age, and 15 to 19 mg for adults, including those who are pregnant or lactating [ 56 ].

Vitamin E is an antioxidant that plays an important role in immune function by helping maintain cell membrane integrity and epithelial barriers and by enhancing antibody production, lymphocyte proliferation, and natural killer cell activity [ 4 , 5 , 15 , 17 , 25 , 58 , 79 , ].

Vitamin E also limits inflammation by inhibiting the production of proinflammatory cytokines [ ]. Human and animal studies suggest that vitamin E deficiency impairs humoral and cell-mediated immunity, is associated with reduced natural killer cell activity, and increases susceptibility to infections [ 5 , , ].

Frank vitamin E deficiency is rare, except in people with intestinal malabsorption disorders [ 56 , 79 ]. Research on the ability of vitamin E to improve immune function tends to use supplemental vitamin E rather than simply ensuring that study participants achieve adequate vitamin E status because it is thought that higher doses may be needed to achieve beneficial effects [ ].

However, study findings have been mixed. However, vitamin E supplementation did not affect the risk of death from pneumonia within 30 days of the initial hospitalization.

A few clinical trials that have examined the effects of vitamin E supplementation on respiratory tract infections in infants and young children or in older adults suggest that vitamin E offers limited benefits and might even increase symptom severity.

A clinical trial in a low-income urban area in India examined the effects of mg alpha-tocopherol and mg ascorbic acid twice daily or placebo for 5 days in infants and young children age 2 to 35 months who were hospitalized with severe acute lower respiratory tract infections and receiving standard care [ ].

Supplementation did not affect the time required to recover from illness. Another clinical trial in which healthy men and women age 60 years or older took one of four different treatments daily for about 15 months identified no benefits and, in fact, found potential risks of vitamin E supplementation to prevent respiratory tract infections.

All but one of the participants had adequate vitamin E concentrations at the start of the study. The vitamin E supplements did not affect the incidence of acute respiratory tract infections throughout the trial.

Moreover, participants who took the vitamin E supplement had longer durations of illness, more severe symptoms including fever and activity restrictions , and greater numbers of symptoms than those who did not take vitamin E. Results were also negative in a similar trial in adults age 65 or older living in nursing homes to determine whether daily supplementation with IU vitamin E 91 mg, as dl -alpha-tocopherol for 1 year reduced the risk of upper or lower respiratory tract infections [ ].

Nutrition per serving 2 tablespoons : 24 calories, 0. Kristi Wempen is a dietitian in Nutrition in Mankato , Minnesota. Skip to main content. Posted By. Kristi Wempen, R. Recent Posts. Speaking of Health. Topics in this Post. Keep the immune system strong While having a healthy immune system is a plus during the season of colds and flu, consider these tips for keeping your immune system strong throughout the year: Focus on a balanced eating plan.

Crack down on spreading germs. Increase sleep, reduce stress. Research demonstrates that lack of sleep and increased stress contribute to illness and overall poor health, so: Adults should get seven to nine hours of sleep each day, while children need eight to 14 hours, depending on age. Healthy ways to cope with stress include meditating, listening to music or journaling.

Physical activity is another strategy to manage stress and may reduce the risk of some chronic diseases that can weaken your immune system. Here are some myths and facts about immune-boosting nutrients: Fact: Chicken soup can help you feel better.

Myth: Vitamin C can prevent illness. Myth: Dairy increases mucus production. Choose immune-boosting nutrients These nutrients play a role in immune health: Beta carotene Beta carotene is found in plant foods, such as sweet potatoes, spinach, carrots, mangoes, broccoli and tomatoes.

Vitamin C Vitamin C-rich foods include citrus fruits, berries, melons, tomatoes, bell peppers and broccoli. Vitamin D Vitamin D is found in fatty fish and eggs.

Shop Everyday Support. Filter: Availability 0 selected Reset. Sort by: Featured Best selling Alphabetically, A-Z Alphabetically, Z-A Price, low to high Price, high to low Date, old to new Date, new to old.

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Add the tomatoes, apples, vinegar and sugar. Mix together and simmer over low heat for 20—30 minutes, stirring occasionally. Season to taste. Nutrition per serving 2 tablespoons : 24 calories, 0. Kristi Wempen is a dietitian in Nutrition in Mankato , Minnesota.

Skip to main content. Posted By. Kristi Wempen, R. Recent Posts. Speaking of Health. Topics in this Post. Keep the immune system strong While having a healthy immune system is a plus during the season of colds and flu, consider these tips for keeping your immune system strong throughout the year: Focus on a balanced eating plan.

Crack down on spreading germs. Increase sleep, reduce stress. Research demonstrates that lack of sleep and increased stress contribute to illness and overall poor health, so: Adults should get seven to nine hours of sleep each day, while children need eight to 14 hours, depending on age.

Healthy ways to cope with stress include meditating, listening to music or journaling. Physical activity is another strategy to manage stress and may reduce the risk of some chronic diseases that can weaken your immune system.

Here are some myths and facts about immune-boosting nutrients: Fact: Chicken soup can help you feel better. Myth: Vitamin C can prevent illness. Myth: Dairy increases mucus production. So, vitamin formulations will do little to help you stay healthy if you are healthy already.

When it comes to probiotics, there is also some truth to the idea that the bacteria and organisms living in your gut may play a role in your health. Someday, scientists may very well be able to tell us how to prevent disease by modifying these various species inside our bodies, which make up what is called the microbiome.

But today, there isn't enough understanding of the complex interplay between the body and the microbiome to effectively use probiotics to improve health. So, if you can't help your immune system by taking an over-the-counter potion or pill, what can you do to cut down on illness this winter?

Differences between people who rarely get sick and those who are sick all the time may have more to do with habits than immune function, says Starnbach. Here are some tips that might help. Clean your hands. While some germs are airborne, more often than not, illness occurs after you touch a contaminated surface, says Starnbach.

Most often germs move from your hands into your eyes, nose, or mouth, so also make an effort not to touch your face. Keep your body in top shape. Maintaining a healthy and balanced diet, exercising regularly, and getting enough sleep can help keep your body and your immune system working well.

Manage stress. Research has shown that high stress levels may impair the immune system. So whenever possible, try to be aware of your stress levels and work to lower them when they get too high.

Get vaccinated. Getting vaccinated against the flu and other diseases stimulates the immune system to protect against illness. Vaccines teach the immune system to recognize specific pathogens and prepare them to mount a defense if they are encountered.

The bottom line is that aside from vaccines, there's really nothing you can take to improve your immune system, so it's probably best to avoid pills and potions that make those types of claims.

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