Vitamin A (Retinol)
Vitamin A may also reduce the risk of infection, anemia, preterm birth, intrauterine growth restriction, and some birth defects; however, research into these aspects of vitamin A is ongoing.
Vitamin A intake during pregnancy is of significant interest due to its potential to cause possible toxic effects in the fetus if the mother takes too little or too much – especially within the first 60 days after fertilization.
The potential for harm from excessive vitamin A during pregnancy was first identified in 1953 in pregnant animals. Pregnant rats were fed 35,000 International Units (IU) of vitamin A per day on days 2 through 16 of gestation, which resulted in brain defects, cleft lip and/or palate, and various eye malformations. Safe levels of vitamin A during pregnancy have been debated ever since.
Researchers do not know exactly why excess vitamin A causes certain birth defects or the highest minimum dose that can be taken during pregnancy without causing birth defects. This answer is critical, as vitamin A is also a vital nutrient necessary for fetal growth.
Safe levels are hard to determine because there is only limited information regarding the effect of pregnancy on the body’s breakdown and use of vitamin A. Further, determining the rate at which vitamin A is transferred from mother to fetus via placenta is also difficult, and could change throughout pregnancy.
Forms of Vitamin A
There are two groups of compounds related to vitamin A: carotenoids (mostly plant foods) and retinols (preformed vitamin A; mostly animal products).
Carotenoids, like beta-carotene, and foods that contain it, are not toxic in normal amounts, as it is not stored or metabolized in the same way in the body as retinoids.
Although it is commonly known that too much vitamin A though food (carotenemia) can turn the skin a yellow-orange (which is harmless), there have only been approximately two dozen cases since 1970 of toxic effects from dietary vitamin A.
Retinoids are a class of medications that are chemically derived from vitamin A, and are used to manage acne, psoriasis, skin aging, and some cancers. Retinoids include acitretin, adapalene, alitretinoin, bexarotene, isotretinoin, tazarotene and tretinoin. They are taken by mouth or applied as creams or gels.
Tigason® (etretinate), used to treat psoriasis, has also been implicated in similar toxic effects, and may continue to cause birth defects up to two years after the medication has been stopped (three reported cases). It has not been determined how long pregnancy should be avoided after discontinuation of treatment, so it is recommended etretinate not be used in women who plan to get pregnant.
Accutane® (isotretinoin), a common medication for severe acne, was first documented to cause birth defects in 1983 when three malformed infants were identified; further evidence indicated the medication can cause major malformations (facial, cardiac, central nervous system) in up to 20% of all exposed fetuses.
The World Health Organization, the American College of Obstetricians and Gynecologists, and the United Kingdom’s National Health Service do not recommend Vitamin A supplementation (beyond a prenatal vitamin) unless a deficiency is identified. At this amount, all vitamin A necessary for pregnancy can be ingested through food.
Fetal vitamin A requirements are believed to be very low until the third trimester, and even then the requirement for vitamin A is estimated to increase only about 10% to 20%.
Further, evidence suggests that pregnant women likely have enough adequate liver stores of the vitamin to last throughout gestation. Vitamin A is fat-soluble, which means that any unused amount gets stored in the fatty tissue of the liver.
If supplementation is necessary during pregnancy, researchers are conflicted regarding at which (supplemental) dose vitamin A becomes harmful, and even at what dosages are considered “high”. Safe dosages have been reported to be less than 30,000 IU/day, while toxic ranges have been reported to range from 10,000 to 30,000 IU/day. This significant overlap illustrates the complexity in studying the vitamin's effects during pregnancy.
Regardless, it is commonly reported that intakes of vitamin A less than 10,000 IU/day during pregnancy have not been associated with birth defects. The World Health Organization recommends limiting intake to a maximum of 10,000 IU/day or 25,000 IU/weekly to minimize risk.
However, the U.S. Food and Drug Administration recommends a maximum of 8,000 IU/day,
Dietary surveys in the U.S. have indicated the average adult diet (food only) contains 7,000 to 8,000 IU/day of vitamin A, but most prenatal preparations contain 8,000 IU/capsule of vitamin A. The U.S. National Academy of Medicine (formerly the Institute of Medicine) has set the daily Upper Limit for pregnant women at 10,000 IU (of only its retinol forms).
For women who want to check their vitamin A levels in their prenatal vitamins, beginning in January 2020, the FDA required manufacturers to switch from IU to retinol activity equivalents (RAE). Therefore:
1 IU retinol = 0.3 mcg RAE
1 IU supplemental beta-carotene = 0.3 mcg RAE
1 IU dietary beta-carotene = 0.05 mcg RAE
1 IU dietary alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE
The current Recommended Dietary Allowance of vitamin A for pregnant woman is 770 mcg RAE. Conversion can only be done if the source of vitamin A is known, but women may obtain vitamin A from potentially three sources in total: animal products, plant foods, and their prenatal vitamin. However, if women obtained vitamin A from only one source, the equivalents are below (for reference only):
Retinol = 2,567 IU
Supplemental beta-carotene = 2,567 IU
Dietary beta-carotene = 15,400 IU
Dietary alpha-carotene or beta-cryptoxanthin = 30,800 IU
It can therefore be assumed that a mixed diet of 770 mcg RAE for women may obtain anywhere from 2,567 to 30,800 IU of all types of vitamin A per day.
The daily upper limit of vitamin A for pregnant women has been set at 3,000 mcg RAE, but only for retinol forms. This equates to 10,000 IU of retinol.
Women need to check their vitamin's label to determine the source of the vitamin A in the vitamin; it could be a combination of retinol and beta-carotene, and they only need to consider the retinol amount.
In general, excess of vitamin A (due to storage in the liver) in a short period of time produces symptoms such as gastrointestinal distress, headaches, blurred vision, vertigo, and muscular incoordination.
Further progression of these symptoms may include drowsiness, fatigue, itching, skin exfoliation, and vomiting, and may lead to respiratory failure or convulsions.
Chronic toxicity usually arises from doses about 10 times the recommended daily limit and can take months to produce symptoms but is usually reversible when supplements are stopped.
The most serious effects of chronic toxicity are on the liver, bones, and vision, where in some cases permanent damage may occur.
Since most individuals in the U.S. have a diet that provides enough vitamin A, deficiency is rare.
Vitamin A deficiency usually occurs in developing countries, and can present with night blindness. Without enough vitamin A, photoreceptors don’t get the pigments necessary for the cells in the retina to work and see the full spectrum of light, causing night blindness. It has been estimated that about 20 million pregnant women in developing countries are affected every year.
Foods high in beta-carotene can provide all necessary amounts of vitamin A required during pregnancy.
Good sources of vitamin A include liver*, carrots, sweet potatoes, pumpkin, cantaloupe (rock melon), eggs, milk, green leafy vegetables, mangoes, and papayas.
*Liver (limit) is very high in vitamin A. Frequent liver consumption could result in intakes above the recommended limit of 770 mcg RAE/10,000 IU; it is recommended pregnant women who consume liver limit their consumption to one serving per day. Cod liver oil should also be avoided during pregnancy for its high vitamin A content.
Women do not have to be concerned about consuming too much vitamin A through food if they eat a regular, varied diet. Further, although the data above is meant to educate, women do not need to tabulate or keep track of how much vitamin A they eat; too much vitamin A is more of a concern regarding supplementation and medication forms. Further, dietary vitamin A is necessary during pregnancy.
However, women who are concerned about their vitamin A intake during pregnancy should talk to their HCP. In addition, women who were previously taking, or are currently taking or using any form of retinoid medication should call their HCP immediately.