Dear Miyuki, 

Cis β-carotene isomers present provitamin A activity. 
We can see in the Recommended Dietary Allowances and in the Dietary reference intakes that we should calculate Retinol Equivalents (RE) and Retinol Activity Equivalent (RAE) according to the following conversion factors: 
RE = 1 μg all- trans retinol + 1/6 μg of dietary all- trans β-carotene + 1/12 μg of other dietary provitamin A carotenoids (NRC, 1989); 
RAE = 1 μg all- trans retinol + 1/12 μg of dietary all- trans β-carotene + 1/24 μg of other dietary provitamin A carotenoids (IOM, 2001). 
So we can read that cis β-carotene isomers should use the conversion factors for "other dietary provitamin A carotenoids”. In Brazil we decided to adopt this approach when data for cis isomers is available. 

References : 
(NRC) National Research Council (1989). Committee on Dietary Allowances. Recommended Dietary Allowances: 10th Edition. Washington, DC. Retrieved August 18, 2014 from: http://www.nap.edu/openbook.php?isbn=0309046335 
(IOM) Institute of Medicine (2001). Dietary reference intakes for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. Washington, DC: National Academies Press. 

Best regards, 

Fernanda Grande 

Department of Food and Experimental Nutrition 
Faculty of Pharmaceutical Sciences 
University of São Paulo (USP), São Paulo, SP, Brazil 
Av. Prof. Lineu Prestes, 580 - Cj. Químicas Bl.14 
CEP 05508-900 São Paulo - Brasil 
Tel: +55 11 99225 0576 

----- Mensagem original -----

> De: "Miyuki Shimizu" <[log in to unmask]>
> Para: [log in to unmask]
> Enviadas: Terça-feira, 4 de Novembro de 2014 8:08:51
> Assunto: Inquiry about vitamin A activity in cis-beta carotene

> Dear, all,

> I’m an intern working at the nutrition division at FAO. I’m currently
> working on the food biodiversity database for cassava crop. In the
> following paper, the retinol equivalents are calculated based on the
> total values of all-trans-beta carotene and cis-beta carotene.
> (Reference: http://pubs.acs.org/doi/abs/10.1021/jf5018302 )

> I’m trying to figure out the metabolism of cis isomer of beta
> carotene, whether it has vitamin A equivalent activity.
> All-trans-beta carotene is the most suitable precursor for vitamin
> A, but several studies have provided the evidence that 9-cis-beta
> carotene is a precursor of 9-cis retinal or retinoic acid. As far as
> I know, there is little evidence that 9-cis-beta carotene is found
> in human plasma since cis-beta carotene is isomerized to all-trans
> beta carotene after its oral administration.

> I would highly appreciate if someone can share their
> information/data/experience regarding the vitamin A activity of
> cis-beta carotene:
> - For VITA in retinol activity (RE) should 9-cis-beta carotene have:
> 1/6 or 1/12 or 0 vitamin activity?
> - For VITA_RAE should 9-cis-beta carotene have: 1/12 or 1/24 or 0
> vitamin activity?
> Could you also then provide your source of evidence?

> Thank you in advance for your attention to this matter.

> Reference:
> Beta - Carotene : The Controversy Continues .
> http://www.altmedrev.com/publications/5/6/530.pdf
> Evidence of cis-trans isomerization of 9-cis-beta-carotene during
> absorption in humans.
> http://ajcn.nutrition.org/content/64/2/177.short

> Best regards,
> Miyuki Shimizu, MS, RD
> Nutrition Intern
> Food and Agriculture Organization of the United Nations (FAO)
> Nutrition Education and Consumer Awareness Group (ESNE)
> Nutrition Division (ESN)
> Viale delle Terme di Caracalla, 00153
> Rome, Italy
> Room : B246
> Tel.: +39 06570 55899
> Website : http://www.fao.org/food/en/

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