The excretion of vitamin A in urine

Meeting the Vitamin A Requirement: The Efficacy and Importance of β-Carotene in Animal Species

Vitamin A is essential for life in all vertebrate animals. Vitamin A requirement can be met from dietary preformed vitamin A or provitamin A carotenoids, the most important of which is β-carotene. The metabolism of β-carotene, including its intestinal absorption, accumulation in tissues, and conversion to vitamin A, varies widely across animal species and determines the role that β-carotene plays in meeting vitamin A requirement. This review begins with a brief discussion of vitamin A, with an emphasis on species differences in metabolism. A more detailed discussion of β-carotene follows, with a focus on factors impacting bioavailability and its conversion to vitamin A. Finally, the literature on how animals utilize β-carotene is reviewed individually for several species and classes of animals. We conclude that β-carotene conversion to vitamin A is variable and dependent on a number of factors, which are important to consider in the formulation and assessment of diets. Omnivores and herbivores are more efficient at converting β-carotene to vitamin A than carnivores. Absorption and accumulation of β-carotene in tissues vary with species and are poorly understood. More comparative and mechanistic studies are required in this area to improve the understanding of β-carotene metabolism.

Bioavailability of iron, vitamin A, zinc, and folic acid when added to condiments and seasonings

Seasonings and condiments can be candidate vehicles for micronutrient fortification if consumed consistently and if dietary practices ensure bioavailability of the nutrient. In this review, we identify factors that may affect the bioavailability of iron, vitamin A, zinc, and folic acid when added to seasonings and condiments and evaluate their effects on micronutrient status. We take into consideration the chemical and physical properties of different forms of the micronutrients, the influence of the physical and chemical properties of foods and meals to which fortified seasonings and condiments are typically added, and interactions between micronutrients and the physiological and nutritional status of the target population. Bioavailable fortificants of iron have been developed for use in dry or fluid vehicles. For example, sodium iron ethylenediaminetetraacetic acid (NaFeEDTA) and ferrous sulfate with citric acid are options for iron fortification of fish and soy sauce. Furthermore, NaFeEDTA, microencapsulated ferrous fumarate, and micronized elemental iron are potential fortificants in curry powder and salt. Dry forms of retinyl acetate or palmitate are bioavailable fortificants of vitamin A in dry candidate vehicles, but there are no published studies of these fortificants in fluid vehicles. Studies of zinc and folic acid bioavailability in seasonings and condiments are also lacking.

Safety evaluation of vitamin A in growing dogs

The safe upper limit for inclusion of vitamin A in complete diets for growing dogs is uncertain, with the result that current recommendations range from 5.24 to 104.80 μmol retinol (5000 to 100 000 IU vitamin A)/4184 kJ (1000 kcal) metabolisable energy (ME). The aim of the present study was to determine the effect of feeding four concentrations of vitamin A to puppies from weaning until 1 year of age. A total of forty-nine puppies, of two breeds, Labrador Retriever and Miniature Schnauzer, were randomly assigned to one of four treatment groups. Following weaning at 8 weeks of age, puppies were fed a complete food supplemented with retinyl acetate diluted in vegetable oil and fed at 1 ml oil/100 g diet to achieve an intake of 5·24, 13·10, 78·60 and 104·80 μmol retinol (5000, 12 500, 75 000 and 100 000 IU vitamin A)/4184 kJ (1000 kcal) ME. Fasted blood and urine samples were collected at 8, 10, 12, 14, 16, 20, 26, 36 and 52 weeks of age and analysed for markers of vitamin A metabolism and markers of safety including haematological and biochemical variables, bone-specific alkaline phosphatase, cross-linked carboxyterminal telopeptides of type I collagen and dual-energy X-ray absorptiometry. Clinical examinations were conducted every 4 weeks. Data were analysed by means of a mixed model analysis with Bonferroni corrections for multiple endpoints. There was no effect of vitamin A concentration on any of the parameters, with the exception of total serum retinyl esters, and no effect of dose on the number, type and duration of adverse events. We therefore propose that 104·80 μmol retinol (100 000 IU vitamin A)/4184 kJ (1000 kcal) is a suitable safe upper limit for use in the formulation of diets designed for puppy growth.

Complex interactions with infection and diet may explain seasonal growth responses to vitamin A in preschool aged Indonesian children

OBJECTIVE

To explore the potential contribution of respiratory infections and vitamin A intakes to the seasonal effect of vitamin A supplementation on child growth.

METHODS

Data from a randomized double-blind placebo-controlled trial, in which a single high dose of vitamin A or placebo was given every 4 months to 1405 children aged 6-48 months were used for the analysis. In total, 4430 child-treatment cycles were examined, and for each cycle the children had their dietary intake, weight, and height assessed at the start and end. Linear regression models of the difference in height and weight during each treatment cycle were used and the within-child correlation was adjusted using the generalized estimating equations (GEE). Other covariables in the model included age, sex, percentage of days with acute lower respiratory infection and diarrhea, and cumulative doses of vitamin A.

RESULTS

This study showed that a significant effect of vitamin A supplementation on linear growth was observed in all seasons in children with a low burden of respiratory infections, that is, < 21.5% of days with respiratory illness. In each season, the highest effect was found in children with a low burden of respiratory infections and low vitamin A intakes, that is, intakes < 400 RE/day. Children with a high burden of respiratory infections or high vitamin A intakes benefited less from vitamin A supplementation for their linear growth than children with a low burden of respiratory infections and low vitamin A intakes. Finally, there was no benefit for linear growth from vitamin A supplementation in children with both a high burden of respiratory infections and high vitamin A intakes regardless of the season.

CONCLUSIONS

The effect of vitamin A supplementation on growth is dependent on season. Respiratory infections and vitamin A intakes are important factors underlying the seasonal effect of vitamin A supplementation on growth.

Why do children become vitamin A deficient?

Vitamin A deficiency is very prevalent and contributes substantially to morbidity and mortality among young children in developing countries. We identify and quantify three causes of vitamin A deficiency in young children based on data available in the literature: maternal vitamin A deficiency resulting in low concentrations of vitamin A in breast milk, inadequate dietary intake of vitamin A during and after weaning and prevalent illness. We developed a set of recursive equations to estimate the amount of vitamin A in the liver as a function of age over the first 2 y of life. To apply the equations, we selected a best estimate value for each input parameter as the most representative of a typical child in a developing country. Because of the great variability that exists for each variable, we also carried out sensitivity analyses, substituting more extreme values for input parameters. We then estimated stores, assuming a child in a developing country also receives the newly revised vitamin A supplementation regimen recommended by the World Health Organization. Without supplementation, a typical child in a developing country is not able to attain and maintain "minimally adequate" liver vitamin A stores. To overcome this deficit by eating fruits and vegetables alone, the child would need to increase portion sizes about 10-fold. If the child receives the new supplementation regimen, his or her liver stores will still be far short of the average American child (i.e., exceedingly far from toxic levels). However, our estimates indicate that the new supplementation regimen will permit a typical child in a developing country setting to attain minimally adequate vitamin A stores during the first 2 y of life.

Mortality associated with mild, untreated xerophthalmia

The high mortality rate among children with severe corneal xerophthalmia is well recognized. The present study investigates, for the first time, mortality among the very much larger number of otherwise healthy free-living children with mild xerophthalmia (night blindness and Bitot's spots). An average of 3481 children (under 6 years of age) living in six Indonesian villages were reexamined by an ophthalmologist, pediatrician, and nutritionist every 3 months for 18 months. The overall prevalence of mild xerophthalmia was 4.9%. During the 18 months of observation, 132 children died. Of these, 24 had mild xerophthalmia and 108 had normal eyes at the 3-monthly examination preceding their death. Mortality rates were calculated for each 3-month interval by classifying all children by their ocular status at the start of the interval, and then dividing the number of deaths within the interval by the number of children of the same ocular status followed up for that interval. Mortality rates for the six 3-month intervals were then added together, and the results expressed as deaths per 1000 "child-intervals" of follow-up. Overall mortality rates for children with mild xerophthalmia and for children with normal eyes were 23.3 and 5.3, respectively, a ratio of 4 to 1. Excess mortality among the mildly xerophthalmic children increased with the severity of their xerophthalmia. Mortality rates for children with night blindness, with Bitot's spots, and with the two conditions concurrently were 2.7, 6.6, and 8.6 times the mortality rate of non-xerophthalmic children. This direct, almost linear relation between mortality and the severity of mild xerophthalmia was still present after standardizing for age and for the presence or absence of respiratory infection and protein-energy malnutrition. In the population studied, 16% of all deaths in children 1 to 6 years of age were directly related to vitamin A deficiency identified by the presence of mild xerophthalmia. These results suggest: that the existence of mild vitamin A deficiency in a community justifies initiation of vigorous intervention measures to reduce mortality, as much as to prevent the rarer cases of blindness; that night blindness and Bitot's spots should be accorded the same respect as is low "weight for height" in identifying those children in urgent need of medical attention; that ocular criteria used for determining the existence and severity of a vitamin A problem be reevaluated; and that the ophthalmic community, which has long been responsible for managing xerophthalmia, must now re-alert nutritionists, pediatricians, and public health workers to the serious systemic consequences accompanying even mild

Absorption of labelled vitamin A in children during infection

1. The intestinal absorption of [11,123H2] retinyl acetate was studied in five apparently normal children, eight children with respiratory infection and three with gastroenteritis.

2. The absorption of vitamin A was significantly lower in children with respiratory infection or gastroenteritis than in normal children.

3. In the light of these observations, it is suggested that repeated attacks of infections may significantly contribute to the prevalence of vitamin A deficiency in children of poor communities.