Vitamin A and immunity: do supplements prevent infections?

What does vitamin A do for immunity?

The immune system is a network, not a single switch. Skin and the linings of the airways and gut help form barriers, while immune cells respond to infections. Vitamin A helps maintain these tissues and normal immune responses. One form the body makes, retinoic acid, helps regulate how cells develop and behave. This is a description of normal biology, not a test showing an extra supplement prevents illness.27

Does deficiency make a difference?

A sustained shortage can impair those barriers and immune responses and is associated with greater susceptibility to infection. Deficiency can arise from inadequate intake or problems absorbing fat. The likelihood varies between people and places. A health professional can consider food intake, medical history, symptoms and appropriate tests; repeated infections do not by themselves diagnose a vitamin deficiency.

Read how deficiency is assessed and why some children’s programmes are targeted to particular settings.28

Will extra vitamin A prevent colds?

It is not established as a general cold-prevention strategy. A 2024 Cochrane review included six trials in children up to seven in lower- and middle-income countries. The authors found that vitamin A may offer no benefit for preventing upper respiratory infections, but considered the evidence uncertain and of low or very low confidence. The six studies involved 27,351 participants, but only three could be pooled for one infection-frequency outcome; two studies also gave vitamin E. Evidence was searched through June 2023. Only one study, with 116 participants, reported adverse events; that limited reporting cannot establish safety across the other studies. The review does not settle every question for a child with deficiency, and it is not a trial in all adults.4

The US National Institutes of Health notes that, without a deficiency, extra vitamins and minerals usually do little to prevent specific infections or speed recovery. That does not mean an identified deficiency should be ignored. In a 2021 review, a subgroup from three trials found more acute respiratory infections among normally nourished children given vitamin A above WHO programme recommendations. The trials varied and the subgroup finding does not determine risk for every child. It is distinct from targeted programmes for children at risk of deficiency.321

What if vitamin A is low during an infection?

Illness and inflammation can affect the amount of retinol measured in blood, so one low result during an infection does not by itself show what a person’s long-term stores were before becoming ill. In a small 1996 study of children hospitalized with respiratory syncytial virus (RSV), blood vitamin A was low during illness. The trial then compared vitamin A in 21 children with placebo in 11 and found no clear difference in measures including severity or length of hospital stay.

The study was small and concerned treatment of hospitalized children with RSV—not prevention of colds or every infection. A non-significant result does not prove there can never be a benefit. It illustrates why an association between a blood level and illness is not enough to establish what a supplement will do.598

Why is measles different?

Measles can cause serious complications, and WHO recommends clinician-directed vitamin A as part of care for suspected measles in children under five. This is different from taking a supplement to prevent an ordinary cold. Vitamin A is not a reliable way to prevent measles and does not replace vaccination. If measles is suspected, seek prompt medical advice and call ahead before visiting where possible; severe symptoms need urgent care. See vitamin A, children and measles for the care context.101112

Can “immune support” products cause harm?

Products may combine vitamins with other ingredients or overlap with a multivitamin or cod liver oil. Too much preformed vitamin A can be harmful, particularly in pregnancy; high-dose beta-carotene supplements have a different concern for people who smoke or used to smoke. A label saying “immune support” does not tell you whether a product prevents an infection, whether it was studied, or whether two products overlap. See vitamin A labels and overlap and too much vitamin A.37

What else affects infection risk?

Adequate nutrition matters, but it is one part of a larger picture. The US CDC lists measures such as recommended vaccines, hand hygiene and cleaner indoor air to reduce respiratory infections; recommendations and eligibility vary locally. If infections are unusually frequent, severe or concerning, a health professional can assess possible causes rather than relying on a supplement claim. Return to the vitamin A overview or explore vitamins and multivitamins. For a broader view of vaccines, peptides and nutrients, see what immune-support claims mean.63