Safety of Vitamin A Intake During Pregnancy

Studies have shown a link between taking high doses of Vitamin A (as retinol or retinyl esters) during early pregnancy and certain birth defects. How much and what forms of Vitamin A is safe during pregnancy? Are there other medications or foods that should be avoided?

Recommended Intake During Pregnancy

Vitamin A is required and essential for maintenance of normal reproductive function. The recommended daily level during pregnancy is 8,000 IU". Doses of Vitamin A, consumed as retinol of more than 10,000 IU can be harmful to unborn children.

Two Types of Vitamin A

Vitamin A is available in two forms -- the water-soluble provitamin, beta-carotene, coming from plants and retinoid, a preformed vitamin A originating from animal tissue. Beta carotene, in any dose, is not associated with birth defects. Fruits such as carrots, tomatoes, kale and spinach are good sources of this vitamin.

Vitamin A as Retinol

Retinol is a fat soluble vitamin found mainly in liver, egg yolks, and the fat component of dairy products. The maximum

How You Can Be Safe

Several recommendations have been made for vitamin A intake by pregnant women. The FDA has recommended that pregnant women obtain vitamin A in the form of beta-carotene whenever possible (FDA Talk Paper; October 6, 1995). According to the FDA, "beta-carotene is a substance found naturally in plants, and it can be converted to vitamin A in the body. It is considerably less toxic than the pre-formed vitamin A. Therefore, women of child-bearing age are advised to choose fortified foods that contain vitamin A in the form of beta-carotene rather than pre-formed vitamin A, whenever possible. The vitamin A in fruits and vegetables is naturally in the form of beta-carotene, and high intakes of vitamin A from these sources are generally not of concern. Taking too little vitamin A can result in adverse effects just as can taking in too much. The key is in finding the 'right amount' through carefully reading product nutrition labeling."

In 1995, a study regarding possible adverse fetal effects of high doses of Vitamin A by women in

Also, it should be recognized that concurrent ingestion of retinol from high concentration vitamin A foods, especially frequent ingestion of liver, can contribute to the overall total amount of retinol consumed daily.

While the conclusions of the Boston study are basically in keeping with those above, one criticism of that study is the definition of malformation and the presumption that these defects are all the result of aberrant cranial neural crest cell migration. Retinoid embryopathy, a syndrome of anomalies involving the face, ear, heart, central nervous system and thymus, derives primarily from defects in migration of cranial neural crest cells. Previous experimental laboratory investigations and the clinically described retinoid embryopathy associated with other vitamin A analogs such as isotretinoin (Accutane), have linked high levels of exposure to these analogs (not beta-carotene) with abnormal migration of cranial neural crest cells early in embryonic development. It could be expected that vitamin A as retinol and retinyl esters may induce similar defects.

Unfortunately, the Boston investigators did not distinguish the cranial neural crest cell derived defects from others in their study. The research team included ALL CNS defects (except neural tube defects) as well as ALL heart defects in this category of cranial neural crest cell derived defects. Such broad categorization includes a number of defects (e.g. hydrocephalus), which may not be of cranial neural crest origin at all. Thus, possible misclassification confounds the conclusions drawn. In summary, if a woman is taking a multivitamin, prenatal vitamin or Vitamin A supplements containing less than 10,000 IU (as retinol or retinyl), or beta-carotene at any dose, there is no evidence of an increase in the risk of malformations in her baby.

References:

  1. Rothman KJ, Moore LL, Singer MR, Nguyen U-SDT, Mannino S, Milunsky A (1995): Teratogenicity of high vitamin A intake.N Engl J Med 333:1369-1373.
  2. Oakley GP Jr, Erickson, JD (1995): Vitamin A and Birth Defects (Editorial). Ibid 333:1414-1415.