Chemistry Reference
In-Depth Information
adequate to maintain normal plasma concentrations of retinol and protect
against a vitamin A deficiency for approximately 4 months while the person
consumes a vitamin A-deficient diet. The estimated average requirement
(EAR) of preformed vitamin A required to assume an adequate body reserve
in men
>
19 years is 625 mg RAE/day, and for women the EAR is 500 mg RAE/
day. The recommended dietary allowance (RDA) for vitamin A is set using a
coefficient of variation (CV) of 20% and the EAR for adequate stores of
vitamin A. The RDA is defined as equal to the EAR plus twice the CV to
cover the needs of 97-98% of the individuals in the group. The RDAs for men
and women are 900 and 700 mg RAE/day, respectively. In Europe, the
Scientific Committee for Food (1993) set a population reference intake
(PRI) of 700 and 600 mg retinol equivalent/day for men and women,
respectively.
When ingested in large doses, vitamin A can be toxic (Ross, 1999a).
Acute toxicity is produced by one or several closely spaced, very large doses of
vitamin A, usually
>
100 times the recommended intake in adults and
>
20
times the recommended intake for children (Olson et al., 2000). Chronic
toxicity, which arises from ingestion of doses greater than or equal to
30,000 mg/day for months or years, is a major cause for concern (Food and
Nutrition Board, 2001). The symptoms of toxicity include headache, vomit-
ing, alopecia, cracking of lips, ataxia and anorexia. Permanent damage to
liver, bone and vision, as well as chronic muscular and skeletal pain, may
result (Ross, 1999a). Chronic excessive vitamin A intake has been shown to
lead to bone mineral loss in animals (Rohde et al., 1999) and may also be
associated with osteoporosis and increased risk of hip fracture in humans
with intakes of 1.5-2.0 mg of retinol/day (Promislow et al., 2002; Penniston
and Tanumihardjo, 2003, 2006). Concern for the possible teratogenicity of
high vitamin A intake in humans is based on the unequivocal demonstration
of human teratogenicity of 13-cis-retinoic acid (Eckhoff et al., 1991;
Armstrong et al., 1994). The most serious teratogenic effects of vitamin A
include fetal resorption, abortion, birth defects and permanent learning dis-
abilities in the progeny.
No adverse effects other than carotenodermia, which is characterized
by a yellowish discolouration of the skin, have been reported from the
consumption of
-carotene or other carotenoids in foods (Food and Nutri-
tion Board, 2000). In addition, long-term supplementation with
-carotene to
persons with adequate vitamin A status does not increase the concentration
of serum retinol (Nierenberg et al., 1997). The tolerable upper limit (UL) for
vitamin A for men and women
19 years is set at 3,000 mg/day of prefor-
med vitamin A (Food and Nutrition Board, 2001). A UL has not been set for
-carotene or other carotenoids.
