Just an addendum concerning safety of vitamin A.
First, here is a list of vitamin A content of a few foods, in IUs per 100 grams.
The richest source is obviously liver.
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Beef liver, raw 35346
Beef liver, cooked, braised 35679
Lamb liver, raw 24612
Chicken liver, raw 20549
Butter 3058
Egg yolk, raw 1945
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As seen below, vitamin A is important for child development, but intakes much
higher than 10000 IUs a day are not recommended, especially for pregnant women
(teratogenicity=risk of birth defects). This corresponds to about 1.5 chicken
liver/day, or 1 oz. beef liver/day. So, risks indeed exist, but people eating
much more than 1.5 chicken liver/day are probably rare.
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Am J Med 1994 Dec;97(6):523-528, Vitamin A hepatotoxicity: a cautionary note
regarding 25,000 IU supplements, Kowalski TE, Falestiny M, Furth E, Malet PF
Vitamin A hepatotoxicity has been reported at doses exceeding 50,000 IU/day.
At 25,000 IU vitamin A per day, although elevated liver enzymes may be seen,
hepatotoxicity is rare. We report a case of severe hepatotoxicity associated
with the habitual daily ingestion of 25,000 IU of vitamin A bought as an
over-the-counter dietary supplement. With the general availability of
high-dose supplements and recent literature emphasizing the importance of
vitamin A adequacy, the potential for vitamin A hepatotoxicity may increase.
Health professionals should remain aware of the potential for vitamin A
hepatotoxicity and elicit a vitamin A history in all patients being evaluated
for liver dysfunction.
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N Engl J Med 1995 Nov 23;333(21):1369-1373, Teratogenicity of high vitamin A
intake, Rothman KJ, Moore LL, Singer MR, Nguyen US, Mannino S, Milunsky A
BACKGROUND. Studies in animals indicate that natural forms of vitamin A
are teratogenic. Synthetic retinoids chemically similar to vitamin A cause
birth defects in humans; as in animals, the defects appear to affect tissues
derived from the cranial neural crest.
METHODS. Between October 1984 and June 1987, we identified 22,748 pregnant women
when they underwent screening either by measurement of maternal serum
alpha-fetoprotein or by amniocentesis. Nurse interviewers obtained information
on the women's diet, medications, and illnesses during the first trimester of
pregnancy, as well as information on their family and medical history and
exposure to environmental agents. We obtained information on the outcomes of
pregnancy from the obstetricians who delivered the babies or from the women
themselves. Of the 22,748 women, 339 had babies with birth defects; 121 of
these babies had defects occurring in sites that originated in the cranial
neural crest.
RESULTS. For defects associated with cranial-neural-crest tissue, the
ratio of the prevalence among the babies born to women who consumed more
than 15,000 IU of preformed vitamin A per day from food and supplements to
the prevalence among the babies whose mothers consumed 5000 IU or less per
day was 3.5 (95 percent confidence interval, 1.7 to 7.3). For vitamin A from
supplements alone, the ratio of the prevalence among the babies born to
women who consumed more than 10,000 IU per day to that among the babies
whose mothers consumed 5000 IU or less per day was 4.8 (95 percent
confidence interval, 2.2 to 10.5). Using a smoothed regression curve, we found
an apparent threshold near 10,000 IU per day of supplemental vitamin A. The
increased frequency of defects was concentrated among the babies born to
women who had consumed high levels of vitamin A before the seventh week of
gestation.
CONCLUSIONS. High dietary intake of preformed vitamin A appears to be
teratogenic. Among the babies born to women who took more than 10,000 IU of
preformed vitamin A per day in the form of supplements, we estimate that about 1
infant in 57 had a malformation attributable to the supplement.
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Am J Clin Nutr 1994 Feb;59(2 Suppl):517S-522S, Maternal vitamin A status and its
importance in infancy and early childhood, Underwood BA
Early fetal vitamin A supplies must be regulated to avoid teratogenic
consequences from too little or too much. Late in gestation, adequate maternal
vitamin A status is important for newborn reserves and for sustaining
adequate breast-milk concentrations. Vitamin A supplements are not needed
for most pregnant women in Western countries who consume the
recommended dietary allowance during their reproductive years. Increased
consumption of vitamin A-rich foods can meet increased needs during
lactation. Women in developing countries whose habitual intakes are near
basal needs should receive an additional 100 micrograms retinol equivalents
(RE) during pregnancy and 300 micrograms RE during lactation. Supplements
not above 3000 micrograms RE (10,000 IU) daily are safe for fertile women
where circumstances preclude obtaining the needed increment through diet.
The first postpartum month is the only safe period during which to provide
deficient lactating women with a single high-dose supplement to benefit the
mother and breast-feeding infant for several months.
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