Vitamin A for Immune Function
Vitamin A supplementation reduces child mortality in deficient populations but shows no benefit in well-nourished groups.
Overview
Verdict
How It Works
Dosing & Protocol
Typical dose
- Recommended dose
- 700-900 mcg RAE/day meets requirements; the upper limit for preformed vitamin A is 3,000 mcg RAE/day
- Expected timeframe
- Not established in replete people
Protocol
- form
- Beta-carotene is the safer supplemental form, since conversion is regulated; retinol and retinyl palmitate accumulate and cause toxicity
- duration
- Ongoing dietary adequacy rather than a course
- co factor
- Take with fat-containing food. Evidence is mixed and depends entirely on baseline status. Vitamin A is genuinely essential for immunity: it maintains epithelial barrier integrity, supports mucosal IgA production and regulates T-cell differentiation, and deficiency substantially increases mortality from measles and diarrhoeal disease in children. WHO supplementation in deficient populations reduces childhood mortality, which is among the better-established public health interventions. In vitamin A-replete populations, supplementation shows no immune benefit, and some trials of high-dose vitamin A in non-deficient children found increased respiratory infection rates.
- titration
- Do not exceed 3,000 mcg RAE/day (10,000 IU) of preformed vitamin A from all sources
- starting dose
- Meet the RDA - 900 mcg RAE/day for men, 700 mcg RAE/day for women - from food where possible
Evidence
What the studies say
Vitamin A, infection, and immune function
Stephensen, C.B.
Vitamin A deficiency impairs innate immunity by preventing normal regeneration of mucosal barriers damaged by infection and by reducing neutrophil, macrophage and natural killer cell function. It also impairs adaptive immunity, particularly antibody-mediated Th2 responses. Infection itself depresses serum retinol through the acute-phase response, confounding status assessment. Supplementation reduces mortality from measles and diarrhoeal disease in deficient populations, but does not reduce resp
Vitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age
Imdad A, Mayo-Wilson E, Herzer K +1 more
Vitamin A supplementation reduced all-cause mortality in children by about 12% and lowered diarrhoea and measles incidence.
Safety
Caveats
The teratogenicity ceiling is critical: preformed vitamin A above 3,000 mcg RAE (10,000 IU) daily causes birth defects, so women who are or may become pregnant should not exceed the RDA from supplements and should avoid liver, which contains very high retinol levels. Chronic excess in anyone causes hypervitaminosis A - headache, raised intracranial pressure, hair loss, dry skin, bone pain, reduced bone density with fracture risk, and liver damage. Supplemental beta-carotene increased lung cancer in smokers in the ATBC and CARET trials, so smokers and asbestos-exposed workers must avoid it. Interactions include orlistat and cholestyramine reducing absorption, additive toxicity with retinoid drugs such as isotretinoin and acitretin, and potential interaction with warfarin at high doses. For immune function the evidence sits with vaccination, sleep, exercise, not smoking, and correcting deficiencies of vitamin D, zinc, iron and protein. Recurrent severe or unusual infections warrant assessment for immunodeficiency, diabetes or HIV rather than immune supplementation.
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