Vitamin A
Vitamin A is a fat-soluble vitamin required for vision, immune function, reproduction, growth, and maintenance of epithelial tissues.
Overview
Biological role
Vitamin A supports normal vision through retinal pigments, maintains epithelial integrity, contributes to immune function, and is required for growth and reproduction.
Mechanism of action
Retinal participates in the visual cycle; retinoic acid regulates gene expression involved in cell differentiation, immune function, and epithelial maintenance.
Chemical forms
Preformed vitamin A as retinol and retinyl esters; provitamin A carotenoids including beta-carotene. Fat-soluble vitamin stored in the liver; excess risk is mainly from preformed vitamin A in supplements or liver.
Quick answers before choosing a supplement
Chemical forms and absorption
Common forms
Preformed vitamin A as retinol and retinyl esters; provitamin A carotenoids including beta-carotene. Fat-soluble vitamin stored in the liver; excess risk is mainly from preformed vitamin A in supplements or liver.
Absorption context
Dietary fat supports absorption of fat-soluble vitamin A and carotenoids. Carotenoid bioavailability varies by food matrix and preparation.
Clinical use
Established physiology is strong for vision, epithelial integrity, growth, and immunity. Clinical benefit from supplementation depends on deficiency risk and population context.
Absorption and action pathway
What to take with, and what to avoid
Works Well With
Avoid / Use Caution
Best time to take
Frequently asked questions
When is the best time to take Vitamin A?
Take consistently; fat-soluble vitamins are usually best with a meal that contains fat, while water-soluble vitamins are usually flexible.
Can Vitamin A be taken with coffee or milk?
It depends on the vitamin. Fat-soluble vitamins are best with food; water-soluble vitamins are generally more flexible.
Who should be careful with Vitamin A?
Pregnant people, lactating people, infants, and people with fat-malabsorption conditions require careful assessment. Smokers should avoid high-dose beta-carotene supplements unless advised by a clinician.
Food and Intake
| Age / group | Male | Female | Pregnancy | Lactation | Upper limit |
|---|---|---|---|---|---|
| 1-3 years | 300 | 300 | – | – | UL 600 |
| 4-8 years | 400 | 400 | – | – | UL 900 |
| 9-13 years | 600 | 600 | – | – | UL 1,700 |
| 14-18 years | 900 | 700 | 750 | 1,200 | UL 2,800 |
| 19+ years | 900 | 700 | 770 | 1,300 | UL 3,000 |
International reference intake comparison
| Country / authority | Common reference value |
|---|---|
| USA / NIH-FNB | RDA adults 900/700 mcg RAE men/women; pregnancy 770; lactation 1,300; UL 3,000 preformed |
| Europe / EFSA | PRI adults about 750/650 mcg RE men/women; pregnancy 700; lactation 1,300 |
| Australia-New Zealand / NRV | RDI adults 900/700 mcg RE men/women; pregnancy 800; lactation 1,100 |
| Thailand / Thai FDA | Thailand: use Thai RDI and Thai FDA / Ministry of Public Health regulations for labeling and supplement products. Do not interpret labeling values as therapeutic doses; product-specific limits must be checked against the latest notification and formula. |
This table compares reference-intake frameworks across authorities. Values may use different terms such as RDA, AI, PRI, or NRV and should not be merged into one universal dose.
Food source comparison for Vitamin A
| Food | Serving amount | Vitamin A | %DV | %DV bar | Servings to reach 900 mcg RAE |
|---|---|---|---|---|---|
| fried beef liver | 3 oz | 6,582 mcg RAE | 731% | 0.1 | |
| baked sweet potato with skin | 1 item | 1,403 mcg RAE | 156% | 0.6 | |
| boiled spinach | 1/2 cup | 573 mcg RAE | 64% | 1.6 | |
| raw carrot | 1/2 cup | 459 mcg RAE | 51% | 2.0 | |
| vitamin A-fortified milk | 1 cup | 149 mcg RAE | 17% | 6 | |
| boiled egg | 1 egg | 75 mcg RAE | 8% | 12 |
Food values are practical comparison values. Actual content varies by variety, preparation, fortification, and serving size.
Safety
Deficiency
Deficiency can impair dark adaptation and cause xerophthalmia; severe deficiency can lead to blindness and increased susceptibility to infection.
Excess and toxicity
Excess preformed vitamin A can cause toxicity. Chronic high intake is associated with liver abnormalities, reduced bone mineral density, and birth defects when excessive during pregnancy.
Precautions
Pregnant people should avoid high-dose preformed vitamin A unless prescribed. Beta-carotene supplements are not recommended for smoking-related cancer prevention because trials found harm in smokers and asbestos-exposed populations.
Special populations
Pregnant people, lactating people, infants, and people with fat-malabsorption conditions require careful assessment. Smokers should avoid high-dose beta-carotene supplements unless advised by a clinician.
Fast risk map
LOW: insufficient intake
Deficiency can impair dark adaptation and cause xerophthalmia; severe deficiency can lead to blindness and increased susceptibility to infection.
UL: excess intake
Excess preformed vitamin A can cause toxicity. Chronic high intake is associated with liver abnormalities, reduced bone mineral density, and birth defects when excessive during pregnancy.
Precautions: interactions and timing
Pregnant people should avoid high-dose preformed vitamin A unless prescribed. Beta-carotene supplements are not recommended for smoking-related cancer prevention because trials found harm in smokers and asbestos-exposed populations.
SP: special populations
Pregnant people, lactating people, infants, and people with fat-malabsorption conditions require careful assessment. Smokers should avoid high-dose beta-carotene supplements unless advised by a clinician.
Interactions and Clinical Context
Drug interactions
Vitamin A supplements can interact with retinoid medications and may add to toxicity risk. ODS also notes concern with hepatotoxic medicines because high vitamin A intake can affect the liver.
Food interactions
Dietary fat supports absorption of fat-soluble vitamin A and carotenoids. Carotenoid bioavailability varies by food matrix and preparation.
Clinical notes
Established physiology is strong for vision, epithelial integrity, growth, and immunity. Clinical benefit from supplementation depends on deficiency risk and population context.
Evidence level
High for essentiality, deficiency effects, and UL; population-specific for supplementation benefit.