Are you converting enough beta-carotene to vitamin A? Up to 55% of people may not be.

Are you converting enough beta-carotene to vitamin A? Up to 55% of people may not be. 

 
By Katie Clare -  Dip CNM, mBANT, NTCC and CNHC Registered
 
Vitamin A is a group of similar molecules that includes retinol, retinal, and retinoic acid. It is an essential nutrient that we need to get from our diets.  It is needed for growth, healthy skin and hair, mucus membranes, digestive juices, our immune system, and also for good eye health and vision.  Its name, retinol or retinal, comes from its abundance in the retina of the eye.  Vitamin A works with vitamin D to normalise immune tolerance and vitamin A deficiency predisposes individuals to gut mucosal damage.1 Vitamin A levels are also important in thyroid health as it is needed for the uptake of Iodine2 and is required for the thyroid hormone triiodothyronine (T3) to bind to intracellular receptors.3
 

It is well established that the human body can convert beta-carotene (a brightly coloured pigment found in fruits and vegetables) into retinol, so beta- carotene is considered a vitamin A precursor. For decades beta-carotene has been presented as the recommended way to meet most, if not all, of our vitamin A requirements. This is due to concerns dating from the 1980s about possible toxicity from excess retinol and so called ‘hyper-vitaminosis A’. Beta-carotene is thought to have the advantage of only being converted into retinol when it is needed in the body, and so has been presented as the safer option. In particular, this recommendation has been given to women of reproductive age, due to concerns about excess retinol harming the foetus, causing malformations such as tiny ear canals, facial disfiguration or a cleft lip and palate. Until only very recently you would never find much, if any, retinol in a multi-vitamin designed for pregnancy or fertility.  Many vegans or vegetarians choose beta-carotene as their source of vitamin A over retinol as it comes from plant-based foods and retinol has only been found in animal products, such as liver, eggs, fish and dairy.

 

However, as we are all well aware, the science of nutrition is moving at a fast pace and it has recently been brought to light that the conversion of beta-carotene to retinol varies considerably among people. 14 years ago researchers in California discovered that only 45 per cent of people could achieve adequate vitamin A status from beta-carotene alone.4 Although this was a small study on just 11 men, this triggered further research on this topic across the globe. At the same time, the studies on retinol toxicity started to be questioned.  Almost 10 years later, researchers from Newcastle University discovered that the reason behind conversion variation is genetic.The Bcmo1 gene (short for beta-carotene 15,15'-monooxygenase), expresses itself as a protein that is a key enzyme in beta-carotene metabolism to vitamin A. Two genetic variants (or single nucleotide polymorphisms (SNPs)) of this gene were identified and it was confirmed that carriers of these genetic variants have a reduced ability to make the conversion to beta-carotene.

 

If somebody does have a genetic polymorphism of the Bcom1 gene then their requirement for vitamin A may be increased and supplementation may be a wise decision. There are similar stories with other nutrients, such as vitamin D. This nutrient acts via its receptor (VDR); polymorphisms of the VDR gene have also been identified and studied. Also of note is the MTHFR gene which converts folate to its active form. Genetic variations here can lead to a depletion of active folate. The lottery of genetics is fascinating and learning about your own ancestral information and carrier status can give great insights into your wellbeing and health concerns.

 


 
References:
  1. Davidson G, Kritas S, Butler R (2007). Stressed mucosa. Nestle Nutr Workshop Ser Pediatr Program.;59:133-1342; discussion 143-146. 
  2. Hess S, Zimmermann M (2004) The effect of micronutrient deficiencies on iodine nutrition and thyroid metabolism. Int J Vitam Nutr Res.;74(2):103-115.
  3. Pizzorno L, Ferril F (2005) Thyroid. In: Jones D, Quinn S eds Textbook of Functional Medicine. Gig Harbour, WA: Institute for Functional Medicine.
  4. Lin Y, Dueker S (2000) Variability of the conversion of beta-carotene to vitamin A in women measured by using a double-tracer study design. Am J Clin Nutr.;71(6):1545-1554.
  5. Leung WC, Hessel S, Méplan C, Flint J, Oberhauser V, Tourniaire F, Hesketh JE, von Lintig J, Lietz G (2009) Two common single nucleotide polymorphisms in the gene encoding beta-carotene 15,15’-monoxygenase alter beta-carotene metabolism in female volunteers. FASEB J. 23(4):1041-1053. doi: 10.1096/fj.08-121962.
 
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