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FAO/WHO. 1988. Requirements of vitamin A, iron, folate and vitamin B12. Report of a Joint FAO/WHO Expert Consultation. Rome, Food and Agriculture Organization.
Requirement and safe level of intake for vitamin A in this report do not differ significantly from those of the 1988 FAO/WHO Expert Consultation except for adapting to the age categories defined in this consultation and during pregnancy. The term safe level of intake used in the 1988 report is retained in this report because the levels in Table 18 do not strictly correspond to the definition of a recommended nutrient intake.
The mean requirement for an individual is defined as the minimum daily intake of vitamin A as presented in μg retinol equivalents (μg RE) to prevent xerophthalmia in the absence of clinical or sub-clinical infection. This intake should account for proportionate bioavailability of preformed vitamin (about 90 percent) and pro-vitamin A carotenoids from a diet that contains sufficient fat (e.g., at least 5–10 g).
Bio-availability of carotenoids varies widely by source (e.g., fibrous green leafy vegetables or soft-tissue fruits). The required level of intake is set to prevent clinical signs of deficiency, allow for normal growth, and reduce the risk of vitamin A – related severe morbidity and mortality on a population basis. It does not allow for frequent or prolonged periods of infections or other stresses.
The safe level of intake for an individual is defined as the average continuing intake of vitamin A required to permit adequate growth and other vitamin A–dependent functions and to maintain an acceptable total body reserve of the vitamin.
Wallingford, J.C. & Underwood, B.A. 1986. Vitamin A deficiency in pregnancy, lactation, and the nursing child. In: Baurenfeind JC, ed. Vitamin A deficiency and its control. p.101–152. New York, Academic Press.
Newman, V. 1994. Vitamin A and breast-feeding: a comparison of data from developed
and developing countries. Food and Nutrition Bulletin, Series: 161–176.
This reserve helps offset periods of low intake or increased need resulting from infections and other stresses. Useful indicators include a plasma retinol concentration above 0.70 μmol/l, that is associated with a relative dose response below 20 percent, or a modified relative dose response below 0.06. For lactating women, breast-milk retinol levels above 1.05 μmol/l (or above 8 μg/g milk fat) are considered to reflect minimal maternal stores because levels above 1.75 μmol/l are common to populations known to be healthy and without evidence of insufficient dietary vitamin A.
Infants and children
WHO/UNICEF/ORSTOM/UC Davis. 1998. Complementary feeding of young children in developing countries: a review of current scientific knowledge. Pp.228. WHO/NUT/98.1. Geneva, World Health Organization.
Vitamin A requirements for infants are calculated from the vitamin A provided in human milk. During at least the first 6 months of life, exclusive breast-feeding can provide sufficient vitamin A to maintain health, permit normal growth, and maintain sufficient stores in the liver.
Newman, V. 1994. Vitamin A and breast-feeding: a comparison of data from developed and developing countries. Food and Nutrition Bulletin, Series: 161–176.
WHO/UNICEF/ORSTOM/UC Davis. 1998. Complementary feeding of young children in developing countries: a review of current scientific knowledge. Pp.228. WHO/NUT/98.1. Geneva, World Health Organization.
Reported retinol concentrations in human milk varies widely from country to country (0.70–2.45 μmol/l). In some developing countries the vitamin A intake of breast-fed infants who grow well and do not show signs of deficiency is from 120 to 170 μg RE/day.
FAO/WHO. 1988. Requirements of vitamin A, iron, folate and vitamin B12. Report of a Joint FAO/WHO Expert Consultation. Rome, Food and Agriculture Organization.
Such intakes are considered adequate to cover infant requirements if the infant’s weight is assumed to be at least at the 10th percentile according to WHO standards.
However, this intake is unlikely to build adequate body stores because xerophthalmia is common in preschool-age children in the same communities with somewhat lower intakes. Because of the need for vitamin A to support the growth rate of infancy, which can vary considerably, a requirement estimate of 180 μg RE/day seems appropriate.
WHO/UNICEF/ORSTOM/UC Davis. 1998. Complementary feeding of young children
in developing countries: a review of current scientific knowledge. Pp.228.
WHO/NUT/98.1. Geneva, World Health Organization.
The safe level for infants up to 6 months of age is based on observations of breast-fed infants in communities in which good nutrition is the norm. Average consumption of human milk by such infants is about 750 ml/day during the first 6 months.
Assuming an average concentration of vitamin A in human milk of about 1.75 μmol/l, the mean daily intake would be about 375 μg RE, which is therefore the recommended safe level. From 7-12 months, human milk intake averages 650 ml, which would provide 325 μg vitamin A daily. Because breast-fed infants in endemic vitamin A–deficient populations are at increased risk of death from 6 months onward, the requirement and recommended safe intake are increased to 190 μg and 400 μg, respectively.
FAO/WHO. 1988. Requirements of vitamin A, iron, folate and vitamin B12. Report of a Joint FAO/WHO Expert Consultation. Rome, Food and Agriculture Organization.
The requirement (with allowance for variability) and the recommended intake for older children may be estimated from those derived for late infancy (i.e., 20 and 39 μg RE/kg body weight/day).
Rahmathullah, L. Reduced mortality among children in Southern India receiving a small weekly dose of vitamin A. N. Engl. J. Med., 323: 929–935.
On this basis, including allowances for storage requirements and variability, requirements for preschool children would be in the range of 200–400 μg RE daily. In poor communities where children 1–6 years old are reported to have intakes of about 100–200 μg RE/day, signs of VAD do occur; in southern India these signs were relieved and risk of mortality was reduced when the equivalent of 350–400 μg RE/day was given to children weekly.
Adults
FAO/WHO. 1988. Requirements of vitamin A, iron, folate and vitamin B12. Report of a Joint FAO/WHO Expert Consultation. Rome, Food and Agriculture Organization.
Estimates for the requirements and recommended safe intakes for adults are also estimated from those derived for late infancy, i.e. 4.8 and 9.3 μg RE/kg body weight/day. Detailed accounts for arriving at the requirement for vitamin A is provided in the FAO/WHO report of 1988
Gregory, J., Foster, K., Tyler, H. & Wiseman, M. 1990. The Dietary and Nutritionl Survey of British Adults. London, HMSO.
and will not be repeated here because there are no new published studies to indicate a need to revise the assumptions on which the calculations were based. The safe intakes recommended are consistent with the per capita vitamin A content in the food supply of countries that show adequate vitamin A status in all sectors of the population. Additional evidence that the existing safe level of intake is adequate for adults on a population basis is provided by an analysis of dietary data from the 1990 survey of British adults in whom there was no evidence of VAD.
Tyler, H.A., Day, M.J.L. & Rose, H.J. 1991. Vitamin A and pregnancy [letter]. Lancet, 337:48–49.
The median intake for another survey of non-pregnant UK women who did not consume liver or liver products during the survey week was 686 μg/day.
Miller, R.K. 1998. Periconceptional vitamin A use: How much is teratogenic? Reproductive Toxicology, 12: 75–88.
Hathcock, J.N. 1997. Vitamins and minerals: efficacy and safety. Am. J. Clin. Nutr., 66: 427–437.
This value is substantially above the estimated mean requirement for pregnant womenand falls quite short of the amount in which teratology risk is reported.
About onethird of the calculated retinol equivalents consumed by the British women came from provitamin A sources (20 percent from carrots).
Pregnancy
National Academy Sciences, Food and Nutrition Board, Institute of Medicine. 1990. Nutrition during pregnancy. Part II. Nutrient supplements. p. 336-341. Washington, DC, National Academy Press.
During pregnancy additional vitamin A is needed for the growth and maintenance of the foetus for providing a limited reserve in the foetal liver and for maternal tissue growth. There are no reliable figures available for the specific vitamin A requirements for these processes.
Newborn infants need around 100 μg retinol daily to meet their needs for growth. During the third trimester the foetus grows rapidly and, although obviously smaller in size than the infant born full term, the foetus presumably has similar needs. Incremental maternal needs associated with pregnancy are assumed to be provided from maternal reserves in populations of adequately nourished healthy mothers.
In populations consuming at the basal requirement, an increment of 100 μg/day during the full gestation period should enhance maternal storage during early pregnancy and allow adequate amounts of vitamin A for the rapidly growing foetus in late pregnancy. However, this increment may be minimal for women who normally ingest only the basal requirement level of vitamin A inasmuch as the needs and growth rate of the foetus will not be affected by the mother’s initial vitamin A reserves.
West, K.P. 1997. Impact of weekly supplementation of women with vitamin A or betacarotene on foetal, infant and maternal mortality in Nepal. In: Report of the XVIII International Vitamin A Consultative Group Meeting. p. 86. 22-26 September. Cairo, Egypt.
A recent study in Nepal, where night blindness is prevalent in pregnant women, provided 7000 μg RE (about 23,300 IU) weekly to pregnant and lactating women (equivalent to 1000 μg RE/day).
This level of intake normalised serum levels of vitamin A and was associated with a decrease in prevalence of night blindness and a decrease in maternal mortality. The findings of this study need to be confirmed. In the interim period, however, it seems prudent, recognising that a large portion of the world’s population of pregnant women lives under conditions of deprivation, to increase by 200 μg the recommended safe level to ensure adequacy of intake during pregnancy.
WHO. 1998. Safe vitamin A dosage during pregnancy and lactation. pp.34. WHO/NUT/98.4. Geneva, World Health Organization.
Because therapeutic levels of vitamin A are generally higher than preventive levels, the safe intake level recommended during pregnancy is 800 μg RE/day. Women who are or who might become pregnant should carefully limit their total daily vitamin A intake to a maximum of 3000 μg RE (10 000 IU) to minimise risk of foetal toxicity.Lactation
If the amounts of vitamin A recommended for infants are supplied by human milk, mothers should absorb at least as much in their diets to replace maternal losses. Thus, the increments in basal and recommended intakes during lactation are 180 μg RE and 350 μg RE, respectively, for the safe recommended intake per day. After the infant reaches the age of 6 months or when solid foods are introduced, the mother’s need for additional amounts of vitamin A lessens.
Elderly
There is no indication that the vitamin A requirements of healthy elderly individuals differs from those of other adults. It should be remembered, however, that diseases that impede vitamin A absorption, storage, and transport might be more common in the elderly than in other age groups.
Recommended safe intakes
FAO/WHO. 1988. Requirements of vitamin A, iron, folate and vitamin B12. Report of a Joint FAO/WHO Expert Consultation. Rome, Food and Agriculture Organization.
Table 18 provides the estimated mean requirements for vitamin A and the recommended safe intakes, taking into account the age and gender differences in mean body weights. For most values the true mean and variance are not known. Values in the table have been rounded. It should be noted that there are no adequate data available to derive mean requirements for any group and, therefore, a recommended nutrient intake cannot be calculated.
However, information is available on cures achieved in a few vitamin A–deficient adult men and on the vitamin A status of groups receiving intakes that are low but nevertheless adequate to prevent the appearance of deficiency-related syndromes. The figures for mean dietary requirements are derived from these, with the understanding that the curative dose is higher than the preventive dose. They are at the upper limits of the range so as to cover the mean dietary requirements of 97.5 percent of the population.
In calculating the safe intake, a normative storage requirement was calculated as a mean for adults equivalent to 434 μg RE/day, and the recommended safe intake was derived in part by using this value + 2 standard deviations. It is doubtful that this value can be applied to deal with growing children. The safe intake for children was compared with the distribution of intakes and comparable serum vitamin A levels reported for children 0–6 years of age from the United States and with distributions of serum levels of vitamin A of children 9–62 months in Australia (103), where evidence of VAD is rare.
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