Measuring beta-carotene bioavailability, bioconversion and vitamin A status in humans.

**Introduction:**Vitamin A is an important micronutrient and populations at risk of Vitamin A deficiency (VAD) includes pregnant and lactating women and school children (1). VAD is usually assessed by serum retinol, a qualitative indicator which is the most common biochemical parameter but it is homeostatically controlled until liver reserves become exteremely low. Recent data from our country using these indicators suggests that although clinical deficiency has declined, marginal vitamin A status may still be prevalent and difficult to diagnose (2). In addition, the effect of sub clinical vitamin A deficiency on human health and the appropriate way to manage it is unknown. The dominant strategy used for the elimination and prevention of vitamin A deficiency has been the use of high dose vitamin A capsules through supplementation programmes. Since Vitamin A overdosing is potentially possible with pre-formed Vitamin A, it does not happen when carotene is ingested. A good source of carotene is green leafy vegetables (GLV), and therefore, using an increased intake of GLV is also a worthwhile method to increase Vitamin A status (stores) in the body. However, when subjects are fed with GLV, it is thought that the carotene is converted into Vitamin A in the body with an efficiency ratio of 12:1 or 8:1 (that is, 8 moles of carotene convert to 1 mole of retinol) (3-7). However, this is not known with accuracy, and the efficiency may vary with nutritional status and source of carotene. Therefore, it is important to measure the beta-carotene bioavailability, bioconversion and vitamin A status in humans accurately before the Vitamin A stores can be measured.

**Justification / need for the study:**Increasing the intake of carotenoids, primarily through beta -carotene, is considered to be a safe way of restoring the vitamin A reserves of an individual because high doses of preformed vitamin A have adverse health effects (3).Since the current vitamin A equivalency ratio for beta -carotene is varying and have large inter-individual variations in both absorption and conversion (4–8), there is a need for quantifying the bioconversion efficiency in targeted population before measuring the their Vitamin A stores.

References:

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2. World Health Organization (WHO). Global prevalence of vitamin A deficiency in populations at risk 1995-2005. WHO Global Database on Vitamin A Deficiency. Geneva: WHO; 2009.
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5. Hickenbottom , S. J. , J. R. Follett , Y. M. Lin , S. R. Dueker , B. J. Burri ,T. R. Neidlinger , and A. J. Clifford . 2002 . Variability in conversion of beta-carotene to vitamin A in men as measured by using a double-tracer study design. Am. J. Clin. Nutr. 75 : 900 – 907 .
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7. Lietz , G. , A. Oxley , W. Leung , and J. Hesketh . 2012 . Single nucleotide polymorphisms upstream from the beta -carotene 15,15 ′ -monoxygenase gene influence provitamin A conversion efficiency in female volunteers. J. Nutr. 142 : 161S – 165S .
8. Sabrina J Hickenbottom, Jennifer R Follett, Yumei Lin, Stephen R Dueker, Betty J Burri, Terry R Neidlinger, Andrew J Clifford, Variability in conversion of β-carotene to vitamin A in men as measured by using a double-tracer study design, The American Journal of Clinical Nutrition, Volume 75, Issue 5, May 2002, Pages 900–907, https://doi.org/10.1093/ajcn/75.5.900