Key points
Retinol and beta-carotene: what is the difference
Who may be short of it
Vitamin A deficiency is above all a problem of low- and middle-income countries, where 190 million children under 5 have it; regular doses there cut the rate of night blindness almost threefold (Imdad A Cochrane Database Syst Rev 2022. PMID 35294044[1]). In other countries, more attention is warranted with alcohol misuse and long-term use of some cholesterol-lowering drugs and laxatives: they reduce the absorption or stores of vitamin A (Burgerstein, Handbuch Nährstoffe 2015, p. 58). The protein that releases vitamin A from the liver's stores depends on zinc (Burgerstein, Handbuch Nährstoffe 2015, p. 55–56) — more in the article Zinc: why you need it, signs of deficiency and how much is safe.
Pregnancy: the main risk of excess
Retinoids — synthetic relatives of vitamin A — cause birth defects, and high doses of preformed vitamin A apparently do too. In a study of 22,748 pregnant women, with supplements of more than 10,000 IU (3,000 µg) a day, defects of the tissues from which the face and head develop occurred more often; the risk is concentrated in the first 7 weeks, when women often do not yet know they are pregnant; by the authors' estimate, the defect was linked to the supplement in about 1 child in 57 (Rothman KJ N Engl J Med 1995. PMID 7477116[2]).
Beta-carotene and smoking
Vitamin A and bones
What the studies showed
| What was tested | Who took part | Result |
|---|---|---|
| Vitamin A doses for children in countries with deficiency, Cochrane review, 2022 | 47 studies, about 1.2 million children | Overall mortality 12% lower, night blindness about three times less common |
| Vitamin A in pregnancy, 1995 | 22,748 pregnant women | Supplements of more than 10,000 IU (3,000 µg) a day: certain defects 4.8 times more often (association) |
| ATBC: 20 mg of beta-carotene for 5–8 years, 1994 | 29,133 male smokers | Lung cancer 18% more often, mortality 8% higher |
| CARET: 30 mg of beta-carotene and 7,500 µg (25,000 IU) of retinol, 1996 | 18,314 smokers, former smokers and people who worked with asbestos | Lung cancer 28% more often, mortality 17% higher |
| Retinol and hip fracture, 18 years, 2002 | 72,337 women after menopause | From 2,000 µg (6,700 IU) a day — risk 1.89 times higher (association) |
Not everything is equally proven: the data on bones and on the benefit of vegetables come from observational studies and show an association, not a cause (Feskanich D JAMA 2002. PMID 11754708[6]; Holick CN Am J Epidemiol 2002. PMID 12226001[9]); no benefit of beta-carotene supplements for cancer prevention has been shown (Druesne-Pecollo N Int J Cancer 2010. PMID 19876916[8]).
Who should be more careful
- Pregnant women and those planning pregnancy: keep track of the total preformed vitamin A and avoid liver (van den Berg H Eur J Obstet Gynecol Reprod Biol 1996. PMID 8735753[7]). Isotretinoin for acne and other retinoids cause birth defects (Rothman KJ N Engl J Med 1995. PMID 7477116[2]) — discuss them with a doctor in advance.
- Smokers and people who worked with asbestos: harm has been shown at 20–30 mg of beta-carotene a day, and the safety of lower supplement doses in smokers has not been established (Druesne-Pecollo N Int J Cancer 2010. PMID 19876916[8]); check the beta-carotene dose on the label of multivitamins and “eye and skin” formulas. Food was not tested in the trials; in smokers, vegetables and fruit were not linked to a higher risk — the risk was lower (association) (Holick CN Am J Epidemiol 2002. PMID 12226001[9]).
- Women after menopause and people with osteoporosis: do not stack retinol from supplements and liver (Feskanich D JAMA 2002. PMID 11754708[6]).
- People taking several supplements: retinol is found in multivitamins, cod liver oil and skin and hair products, and the doses add up.
Bottom line
Vitamin A is essential for vision, skin and immunity, and its main source is a varied diet. Caution applies to high-dose supplements: preformed vitamin A in pregnancy and for bones, beta-carotene pills for smokers. Whether you need supplements, and at what dose, can be discussed at a consultation.
This material is for information only and does not replace a consultation with a doctor. The dose of vitamin A and beta-carotene, especially in pregnancy and for smokers, is determined by a doctor.
References
- Imdad A Cochrane Database Syst Rev 2022. PMID 35294044
- Rothman KJ N Engl J Med 1995. PMID 7477116
- Beta Carotene Cancer Prevention Study Group N Engl J Med 1994. PMID 8127329
- Omenn GS N Engl J Med 1996. PMID 8602180
- Tang G Am J Clin Nutr 2010. PMID 20200262
- Feskanich D JAMA 2002. PMID 11754708
- van den Berg H Eur J Obstet Gynecol Reprod Biol 1996. PMID 8735753
- Druesne-Pecollo N Int J Cancer 2010. PMID 19876916
- Holick CN Am J Epidemiol 2002. PMID 12226001
Key facts
- Regular doses of vitamin A in children aged 6 months to 5 years in countries with deficiency lowered overall mortality by 12% (Imdad A, Cochrane Database Syst Rev 2022).
- The tolerable upper intake level of preformed vitamin A for adults, including pregnant women, is 3,000 µg (10,000 IU) a day; beta-carotene does not count towards it. In women after menopause, a link with fractures is seen from as little as 2,000 µg (6,700 IU) (Institute of Medicine 2001; Feskanich D, JAMA 2002).
- In pregnant women who took more than 10,000 IU (3,000 µg) of preformed vitamin A a day in supplements, certain birth defects in their children occurred 4.8 times more often than at 5,000 IU (1,500 µg) or less (observation, association) (Rothman KJ, N Engl J Med 1995).
- In the ATBC trial, lung cancer occurred 18% more often in male smokers on 20 mg of beta-carotene a day; in CARET, on 30 mg of beta-carotene together with 7,500 µg (25,000 IU) of retinol in smokers, former smokers and people who worked with asbestos, it occurred 28% more often (ATBC Study Group, N Engl J Med 1994; Omenn GS, N Engl J Med 1996).
- In women after menopause who consumed 2,000 µg of retinol (6,700 IU) a day or more with food and supplements, the risk of hip fracture was 1.89 times higher — this is an association, not a proven cause (Feskanich D, JAMA 2002).
