Vitamin A on a supplement label can mean two very different things. It can be preformed vitamin A (retinol or retinyl esters), the kind found in liver, eggs and dairy, which the body uses directly and stores. Or it can be beta-carotene, the orange plant pigment the body converts into vitamin A at a regulated rate. The two have different safety profiles, and for one group of people, smokers, beta-carotene pills have been tested in some of the largest supplement trials ever run.
This guide explains how the forms differ, how to read the units on a label, what the smoker trials found, why preformed vitamin A has an upper limit and beta-carotene does not, and how much vitamin A common products actually contain.
The short version
- Two forms, two risks. Preformed vitamin A (retinol) builds up in the liver and can be toxic in excess; beta-carotene from food is converted only as needed and has not been shown to cause vitamin A toxicity.
- Smokers should avoid high-dose beta-carotene supplements. In two large trials, 20 to 30 mg a day (one trial added retinol) raised lung cancer rates by 18 to 28 percent in smokers, former smokers and asbestos-exposed workers. A US task force recommends that generally healthy, nonpregnant adults not take beta-carotene supplements to try to prevent heart disease or cancer.
- Former smokers: avoid them too, as a precaution. In an eye-health trial, more lung cancers occurred with beta-carotene, almost all in former smokers, though the evidence is smaller and less consistent.
- Mind the upper limit on retinol. Adults should keep preformed vitamin A at or under 3,000 mcg a day (10,000 IU), especially in pregnancy. That limit does not apply to beta-carotene.
- Read the label. Labels now list vitamin A in mcg RAE; the "% as beta-carotene" note is optional unless the product makes a beta-carotene claim, so check the ingredient forms too.
- Most US adults do not need a vitamin A supplement. Deficiency is rare here; a typical multivitamin supplies about a day's worth.
Two kinds of vitamin A
Preformed vitamin A means retinol and its storage forms (retinyl esters such as retinyl palmitate and retinyl acetate). It comes from animal foods, especially liver, and from most supplements. NIH notes that 65 to 80 percent of the vitamin A Americans eat comes in this form. The body absorbs most of it and stores the excess in the liver, which is why too much can build up.
Provitamin A carotenoids are plant pigments, mainly beta-carotene, plus alpha-carotene and beta-cryptoxanthin. The gut converts them into vitamin A using an enzyme called BCO1. Conversion varies from person to person: common gene variants cut conversion by about a third or more in small studies of female volunteers. Animal and cell studies show the gut dials conversion down when vitamin A intake is high. The National Academies' review states that high beta-carotene intake has not been shown to cause vitamin A toxicity; the usual sign of too much is a harmless yellow-orange skin tint that fades when intake falls. Other carotenoids, such as lutein, zeaxanthin and lycopene, are not converted into vitamin A at all. Even so, the Food and Nutrition Board advises against beta-carotene supplements for the general population, except as a source of vitamin A to prevent deficiency. Retinol creams and other topical retinoids are a different exposure and are not covered here.
Reading the units: mcg RAE and IU
US labels now list vitamin A in micrograms of retinol activity equivalents (mcg RAE), replacing the older international units (IU). One mcg RAE equals 1 mcg of retinol, 2 mcg of beta-carotene from a supplement, or 12 mcg of beta-carotene from food. In the old units, 1 IU of retinol and 1 IU of supplemental beta-carotene each equal 0.3 mcg RAE, while 1 IU of food beta-carotene equals only 0.05.
Two practical points. First, the adult Daily Value is 900 mcg RAE (3,000 IU of retinol), and the upper limit of 3,000 mcg applies to preformed vitamin A only. Second, the label is allowed to show the share that comes from beta-carotene (for example, "Vitamin A 1,050 mcg RAE, 43% as beta-carotene"), but under FDA rules that note is optional unless the product makes a beta-carotene claim. If it is missing, check the ingredient list for retinyl acetate or palmitate versus beta-carotene.
One caution on the math: the 2-to-1 supplement factor was worked out at doses under 2 mg, so converting the 15 to 30 mg doses used in trials into mcg RAE gives a label equivalent, not a measured amount of vitamin A.
The evidence at a glance
| The question | Best evidence | What it found | Our read |
|---|---|---|---|
| Do high-dose beta-carotene pills harm smokers? | Two large trials (29,133 and 18,314 people) | More lung cancer and more deaths at 20 to 30 mg a day | Yes; smokers should avoid them |
| Do former smokers share the risk? | An eye-health trial; trial subgroups | More lung cancers with beta-carotene, mostly in former smokers; subgroup results mixed elsewhere | Possible; be cautious |
| Does beta-carotene harm nonsmokers? | Physicians' and Women's Health Studies | No benefit and no harm found | No harm shown, no benefit either |
| Should healthy adults take beta-carotene pills for long-term health? | US Preventive Services Task Force, 2022 | Recommends against them for generally healthy, nonpregnant adults; harms outweigh benefits | No |
| Can beta-carotene cause vitamin A toxicity? | National Academies review | Not shown; no upper limit set | Not shown |
| Can preformed vitamin A be harmful? | NIH; observational studies | Toxic in excess; upper limit 3,000 mcg a day; pregnancy and bone concerns | Yes, above the limit |
These summaries describe research. They are not claims about what a supplement does. Smokers and former smokers should not take high-dose beta-carotene supplements, and women who are or may become pregnant should keep preformed vitamin A at or under 3,000 mcg (10,000 IU) a day.
The smoker trials
In the 1980s, people who ate more fruits and vegetables, and had more beta-carotene in their blood, seemed to get less lung cancer. Two large trials tested whether beta-carotene pills would do the same. Both found the opposite.
ATBC (Finland, 1994). 29,133 male smokers aged 50 to 69 took 20 mg of beta-carotene a day, vitamin E, both or placebo for five to eight years. Lung cancer was 18 percent more common with beta-carotene, and total deaths were 8 percent higher, mainly from lung cancer and heart disease. A later analysis found the excess appeared stronger, though not significantly different, in men who smoked 20 or more cigarettes a day and in those who drank about one drink a day or more.
CARET (United States, 1996). 18,314 smokers, former smokers and asbestos-exposed workers took 30 mg of beta-carotene plus 25,000 IU (7,500 mcg RAE) of retinyl palmitate a day, or placebo. The trial was stopped 21 months early: lung cancer was 28 percent more common in the supplement group and deaths from any cause 17 percent more common. CARET gave both nutrients together, so its harm cannot be pinned on beta-carotene alone, and its retinol dose was two and a half times today's upper limit.
After the pills stopped, the extra risk mostly faded. In ATBC, the excess was gone within 4 to 6 years, and over 18 years of post-trial follow-up lung cancer rates were not raised, though prostate cancer deaths during that period were 20 percent higher in the former beta-carotene group. In CARET, lung cancer and death rates stayed slightly higher for six years after the trial, but the differences were no longer statistically clear. The AREDS2 eye trial is an exception: its extra lung cancers were still seen at 10 years (see below).
Pooled analyses agree. A Cochrane review found about 5 percent more deaths with beta-carotene supplements in the most reliable trials, and a later analysis by dose found the extra deaths at doses above about 10 mg a day. In 2022 the US Preventive Services Task Force concluded with moderate certainty that the harms of beta-carotene supplements outweigh the benefits and recommended against them for preventing cardiovascular disease or cancer in nonpregnant adults living in the community (not in hospitals or nursing homes).
Why would pills behave so differently from carrots? Nobody knows for sure. The contrast shows up even within the same Finnish men: in a later analysis, those with higher blood beta-carotene at the start, mostly from food, had lower death rates. Pills deliver far larger amounts than food, without the rest of the fruit or vegetable, and observational links like this can reflect a healthier overall lifestyle.
Former smokers and the eye-health trial
The original AREDS eye-health formula, tested in people at high risk of advanced age-related macular degeneration, included 15 mg of beta-carotene. Its 2001 report already limited its advice to people "without contraindications such as smoking." In AREDS2, current smokers and people who had quit less than a year earlier were not given beta-carotene, which tested lutein and zeaxanthin as a replacement. Even so, lung cancer was more common with beta-carotene (23 cases, 2.0 percent, vs 11 cases, 0.9 percent), and 31 of the 34 cases were in former smokers. At 10 years the odds of lung cancer were 1.82 times higher with beta-carotene. The trial found that removing beta-carotene did not make the formula less effective for the eyes. The National Eye Institute now marks the original formula as not recommended for current or former smokers.
The former-smoker evidence is not airtight. In CARET's own subgroup analysis, former smokers were the one subgroup whose estimated rise in lung cancer was under 10 percent, and the Physicians' Health Study, in which 39 percent were former smokers, found no significant difference among current and former smokers combined. On the other side, CARET's post-trial follow-up linked the excess deaths from heart and blood vessel disease mainly to women and former smokers. But the AREDS2 result and the size of the stakes make caution reasonable. Our lutein and zeaxanthin guide covers the eye formulas in more detail.
What about nonsmokers?
In people who mostly did not smoke, beta-carotene pills neither helped nor harmed. In the Physicians' Health Study, 22,071 US male doctors were assigned to 50 mg on alternate days or placebo for 12 years, with no difference in cancer, heart disease or deaths. In the Women's Health Study, about 40,000 women were assigned to the same dose or placebo for a median of about 2 years, also with no difference. NIH sums it up: among nonsmokers, beta-carotene and vitamin A supplements do not appear to affect cancer risk. One later analysis found slightly higher scores on a single round of memory and thinking tests (a difference of 0.047 standard units) in older doctors who had taken it for about 18 years, but no difference after 1 year; we found no trial confirming it.
So for nonsmokers the issue is not danger but value: no large trial has shown that beta-carotene pills on their own lower the risk of disease or death in well-nourished adults (in the eye trial, taking it out of the formula made no difference), and the task force recommends against them for disease prevention. Beta-carotene from food is a different matter and is a normal part of a healthy diet.
Too much retinol: liver, pregnancy and bones
Toxicity comes from preformed vitamin A. NIH describes acute toxicity after one or a few very large doses, typically more than 100 times the RDA (severe headache, blurred vision, nausea, dizziness), and chronic toxicity from regular high intake (dry skin, painful joints, fatigue, abnormal liver tests). The adult upper limit of 3,000 mcg a day is based on liver damage in most adults and on birth defects in women who could become pregnant. Alcohol can make vitamin A more toxic.
Pregnancy. In a 1995 study of 22,748 pregnancies, women taking more than 10,000 IU a day of preformed vitamin A from supplements had about 4.8 times the rate of certain birth defects compared with women taking 5,000 IU or less, with the excess concentrated when the high intake happened before the seventh week of pregnancy. A 1997 study comparing mothers of babies with and without birth defects found no such link at those doses, so the threshold is debated, but experts advise women who are or may become pregnant, and those who are breastfeeding, not to take more than 3,000 mcg (10,000 IU) a day from supplements. The upper limit counts food too, and one 3-ounce serving of beef liver alone exceeds it. The oral prescription acne drug isotretinoin, a vitamin A relative, is a proven cause of birth defects. Beta-carotene is not known to cause birth defects.
Bones. Observational studies in Swedish and US adults linked high retinol intake or blood levels to more hip fractures, while beta-carotene was not linked. A large US study of 75,747 women found no overall link, and a 2014 meta-analysis linked high retinol intake to more hip fractures while finding a U-shaped pattern for blood retinol, with both high and low levels tied to more hip fractures. These studies cannot prove cause, but they are another reason not to take extra preformed vitamin A without a need.
How much is in common products
Vitamin A adds up quickly from different sources. Here is what some foods and products contain, from NIH data and product labels we checked on October 31, 2026.
| Source | Form | Vitamin A per serving | Compared with the 3,000 mcg limit |
|---|---|---|---|
| Beef liver, pan fried, 3 ounces (NIH data) | Preformed | 6,582 mcg RAE | About 2 times the limit |
| NOW Vitamin A 25,000 IU softgel | Preformed (retinyl palmitate and fish liver oil) | 7,500 mcg RAE | 2.5 times the limit |
| NOW Vitamin A 10,000 IU softgel | Preformed (retinyl palmitate and fish liver oil) | 3,000 mcg RAE | At the limit |
| Beef liver capsules (one brand, 5 capsules) | Preformed | 1,180 mcg RAE | About 40 percent |
| Common multivitamins (Centrum, One A Day, Nature Made) | Retinyl acetate plus beta-carotene (10 to 60 percent as beta-carotene, by label) | 750 to 1,050 mcg RAE | Under the limit |
| Cod liver oil, 1 teaspoon (labels we checked) | Preformed | 40 to 255 mcg RAE | Under the limit |
| NOW Beta Carotene 7,500 mcg softgel | Beta-carotene (about 15 mg) | 7,500 mcg RAE | Limit does not apply; same daily dose as the original AREDS formula; not for current or former smokers |
Sources: NIH Office of Dietary Supplements and Supplement Facts labels from brand pages and NIH's Dietary Supplement Label Database, read October 31, 2026. Some beef liver products do not declare vitamin A at all, and cod liver oil content varies widely by product.
Two things stand out. Standalone vitamin A products at 25,000 IU (7,500 mcg) are still sold, the same retinol dose given in the CARET trial; the one we checked says on its label that it is not intended for long-term use unless under medical supervision and should not be used in pregnancy. And a 15 mg beta-carotene softgel delivers the daily dose used in the AREDS formula. The product page and label record we read for one such softgel listed cautions for adults only and for pregnancy and nursing but did not mention smoking, while Bausch + Lomb lists its original AREDS formula as not recommended for current or former smokers and its label tells them to consult an eye care professional. If you smoke or used to, do not read a missing warning as a sign of safety. Common multivitamins supply about 0.2 to 1 mg of beta-carotene by our arithmetic, a small fraction of the trial doses. No trial we found was designed to test that amount in smokers, so neither harm nor safety is established at that level.
What should you do?
Vitamin A deficiency is uncommon in the US: NIH reports that fewer than 1 percent of people have low blood vitamin A, even though average intakes from food fall somewhat below the RDA. The RDA is 900 mcg RAE for men and 700 for women (770 in pregnancy, 1,300 while breastfeeding). People more likely to run low include those with cystic fibrosis or conditions that impair fat absorption, such as Crohn's disease, and premature infants; they should follow their clinician's advice.
If you smoke or used to smoke: avoid high-dose beta-carotene supplements and eye formulas that contain beta-carotene; if an eye doctor has recommended an eye formula, choose an AREDS2-style version with lutein and zeaxanthin. Beta-carotene from vegetables and fruit is not the concern. "High-dose" here means amounts like those tested: 15 to 30 mg a day in the trials, and pooled data tie extra deaths to doses above about 10 mg. If you want a multivitamin, you can choose one whose vitamin A comes mainly as retinyl acetate or palmitate rather than beta-carotene.
If you are pregnant or could become pregnant: keep preformed vitamin A from supplements at or under 3,000 mcg (10,000 IU) a day, including what is in your prenatal vitamin, and avoid liver supplements and high-dose cod liver oil unless your clinician agrees. Our pregnancy supplements guide covers this further.
For everyone else: a multivitamin's vitamin A is plenty if you take one at all, and if you want to limit retinol, products that supply part of their vitamin A as beta-carotene are a reasonable choice for nonsmokers. Do not stack a multivitamin with a standalone vitamin A softgel, cod liver oil and liver capsules without adding up the preformed vitamin A. Our multivitamin guide and beef organ rankings have more on those products.
Safety and medicines
- Smokers and former smokers: do not take high-dose beta-carotene supplements. In large trials, 20 to 30 mg a day raised lung cancer in smokers, and an eye-health trial found more lung cancers in former smokers taking 15 mg.
- Upper limit: adults should keep preformed vitamin A (retinol, retinyl palmitate or acetate, liver, cod liver oil) at or under 3,000 mcg RAE (10,000 IU) a day. The limit is lower for children and teens.
- Pregnancy: high preformed vitamin A intake has been linked to birth defects; stay under the limit and ask your clinician before taking liver or cod liver oil products.
- Medicines: oral retinoid drugs such as isotretinoin, acitretin and bexarotene raise the risk of vitamin A toxicity if combined with vitamin A supplements, and the weight-loss drug orlistat reduces absorption of vitamin A and beta-carotene. Ask your pharmacist.
- Liver and alcohol: people with liver disease or heavy alcohol use should avoid extra preformed vitamin A unless a clinician advises it.
Frequently asked questions
What is the difference between retinol and beta-carotene?
Retinol (and its storage forms, retinyl palmitate and acetate) is preformed vitamin A from animal foods and most supplements; the body uses it directly and stores excess in the liver, so too much can be toxic. Beta-carotene is a plant pigment the body converts into vitamin A as needed; high intake has not been shown to cause vitamin A toxicity, and no upper limit has been set for it. Even so, experts advise against beta-carotene supplements for the general population, and smokers and former smokers should avoid high-dose pills.
Why should smokers avoid beta-carotene supplements?
In the ATBC trial, 20 mg a day raised lung cancer by 18 percent in male smokers, and in CARET, 30 mg a day plus retinyl palmitate raised it by 28 percent in current and former smokers and asbestos-exposed workers, with more deaths. Beta-carotene from fruits and vegetables is not the concern; the risk was seen with high-dose pills.
Is beta-carotene safe for former smokers?
Avoiding high-dose beta-carotene pills is the prudent choice. In the AREDS2 eye-health trial, lung cancer was more common with 15 mg of beta-carotene a day (2.0 vs 0.9 percent), and 31 of 34 cases were in former smokers. Other trial subgroups were less consistent, but the National Eye Institute advises current and former smokers not to take the original beta-carotene AREDS formula.
How much vitamin A is too much?
For adults, the upper limit is 3,000 mcg RAE (10,000 IU) a day of preformed vitamin A from food and supplements combined. It does not apply to beta-carotene. A 3-ounce serving of beef liver has about 6,600 mcg RAE, and some single supplements contain 7,500 mcg (25,000 IU), so one product, or a stack of several, can exceed the limit. Smokers and former smokers should still avoid high-dose beta-carotene pills.
How do I convert vitamin A IU to mcg RAE?
For retinol and for beta-carotene in supplements, 1 IU equals 0.3 mcg RAE, so 10,000 IU is 3,000 mcg RAE. For beta-carotene in food, 1 IU equals only 0.05 mcg RAE. The adult Daily Value is 900 mcg RAE.
Is vitamin A safe during pregnancy?
Vitamin A is needed in pregnancy (the RDA is 770 mcg RAE), but high intakes of preformed vitamin A have been linked to birth defects. Experts advise taking no more than 3,000 mcg RAE (10,000 IU) a day from supplements, including a prenatal vitamin. Beta-carotene is not known to cause birth defects. Ask your clinician before taking liver or cod liver oil products.
I smoke. Is the beta-carotene in my multivitamin a problem?
Probably a much smaller concern than high-dose pills. Common multivitamins supply about 0.2 to 1 mg of beta-carotene by our arithmetic, while the harmful trials used 15 to 30 mg a day. No trial we found was designed to test multivitamin amounts in smokers, so neither harm nor safety is established. If you want to avoid it, choose a multivitamin whose vitamin A comes mainly as retinyl acetate or palmitate.
Does vitamin A interact with medicines?
Yes. Oral retinoid drugs such as isotretinoin, acitretin and bexarotene add to vitamin A and raise the risk of toxicity, so avoid vitamin A supplements with them unless your prescriber agrees. The weight-loss drug orlistat lowers absorption of vitamin A and beta-carotene. Ask your pharmacist.
The bottom line
Retinol and beta-carotene both count as vitamin A, but they are not interchangeable. Preformed vitamin A is the one that can build up and cause harm above 3,000 mcg a day, which matters most in pregnancy. Beta-carotene from food is converted as needed and has not been shown to cause vitamin A toxicity, but high-dose beta-carotene pills raised lung cancer in smokers in two large trials, and an eye-health trial found more lung cancers in former smokers.
Most people in the US do not need a vitamin A supplement. If you smoke or used to smoke, skip high-dose beta-carotene and beta-carotene eye formulas. If you are or may become pregnant, keep preformed vitamin A under the limit. If you take several products, add up the preformed vitamin A across all of them, and if you take a retinoid medicine, ask your pharmacist before adding any vitamin A.