Beta-Carotene Is A Retinoid Antagonist

nograde

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There were some trials in the past that showed increased lung-cancer incidence with "Vitamin A" supplementation in smokers. That also led to questions regarding the safety of retinol. Since beta-carotine supplementation was central in those trials the following study seems interesting:

Naturally occurring eccentric cleavage products of provitamin A β-carotene function as antagonists of retinoic acid receptors. - PubMed - NCBI

... These findings suggest that β-apocarotenoids function as naturally occurring retinoid antagonists. The antagonism of retinoid signaling by these metabolites may have implications for the activities of dietary β-carotene as a provitamin A and as a modulator of risk for cardiovascular disease and cancer.

Although the mechanisms responsible for the formation of the eccentric cleavage products of β-carotene in mammals are not fully known, it is clear that some of the long chain β-apocarotenals (e.g. 8′, 10′, 12′, 14′) are found in the plasma of humans (12) and experimental animals (13) and that these are increased under conditions of oxidative stress and high dietary doses of β-carotene (24).

Our analyses of both β-carotene-containing animal diets and fruits containing β-carotene suggest that any dietary source of β-carotene also contains β-apocarotenoids. It may also be useful to consider these findings in attempts to alleviate vitamin A deficiency in humans through the biofortification of crops with high levels of β-carotene.

 
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nograde

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Also note that in recent years a solid correlation between high cobalamin levels and cancer (especially in smokers) has been established. Could it be that b12 increases the production of those beta-carotene cleavage products? The role of b12 in the conversion of beta-carotene into retinol seems to be completely ignored in the scientific literature. Ray is the only one I know of who mentions that connection.
 

Luann

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Has anyone noticed a smell , like body odor, after eating things high in B-carotene (mango, carrot)?

Not really carrot as much. More like mangoes or peaches.
 

Nick Ireland

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Has anyone noticed a smell , like body odor, after eating things high in B-carotene (mango, carrot)?

Not really carrot as much. More like mangoes or peaches.
Yes. Carotenes will make your skin smell odd - they accumulate heavily in subcutaneous fat and also in the liver which can retain a hidden 75% of total reserves - that's a lot of clearing out to do!
 

Nick Ireland

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I wonder what difference the use of Mehtyl B12 would make to those cleavage metabolites? Cobalamin can be very hit and miss for those with methyl issues and is a pretty crude form of the vitamin in my opinion, Methyl b12 made a world of difference for me when I really needed it as part of a detox a few years back. I had been a regular beta carotene user for many years at that point,
 

proteome

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There's been some further research on this:


"A concern is that if you engineer these crops to have unusually high levels of beta-carotene, they might also have high levels of these compounds," Harrison said:
Potential 'dark side' to diets high in beta-carotene

I guess excess beta-carotene Bad, because the excess creates some kind of Vitamin-A/Retinoid antagonist, which, in turn, because of the Thyroid's need for a minimum level, could act similarly to a deficiency?


"These findings may have implications for the unexpected and negative effects of high doses of β-carotene in human clinical trials of cancer prevention (25). An example is the now famous CARET trial, which, based on observational epidemiology, explored whether supplemental β-carotene would decrease incidence of lung cancer in a highly susceptible population, namely smokers and asbestos workers (26, 27). Surprisingly, the supplemented subjects had a higher incidence of disease, and the trial had to be halted early."
 

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