InChristAlone
Member
The teratogenic metabolites of vitamin A in women following supplements and liver - PubMed
Ten healthy female volunteers were given 5 doses of retinol as the palmitate; 50 and 150 mg retinol as an oral supplement, 50 and 150 mg as fried calf liver (50 and 150 g) and 3, 9 or 30 mg by intra-muscular injection. Plasma concentrations of retinyl palmitate were higher after 50 mg retinol...
pubmed.ncbi.nlm.nih.gov
They took 10 female volunteers and gave them either vitamin A supplements or calf liver to eat (50 mg and 150 mg of vit A).
They measured the following retinol metabolites (vitamin A by-products):
- All-trans-retinol
- All-trans-retinyl palmitate
- 13-cis-4-oxo-retinoic acid
- 13-cis-retinoic acid (= isotretinoin)
- All-trans-retinoic acid
- All-trans-4-oxo retinoic acid
All of those metabolites have known teratogenic (birth defect inducing) properties. All metabolites spiked both after the oral supplementation with vitamin A as well as after the consumption of calf liver with equivalent vitamin A content.
But vitamin A supplements caused a significantly higher spike in all-trans-retinoic acid than eating liver (supplements caused a 8 to 20-fold spike of all-trans-retinoic acid as compared to liver).
This led the study authors to express the opinion that the risk of birth defects after eating liver was negligible relative to its potential benefits.
But this conclusion was based on a wrong assumption.
The study authors assumed that the most dangerous of the 6 measured byproducts was all-trans-retinoic acid.
They called it the "principle teratogenic metabolite of retinol".
Given that eating liver caused only an insignificant increase in all-trans-retinoic acid levels (relative to the increase caused by vitamin A supplements), they thought that eating liver was consequently not a concern for pregnant women.
We now know that this assumption is not correct. We know that one of the 6 measured metabolites, 13-cis-retinoic acid (also known as isotretinoin) is highly teratogenic. It can cause birth defects in up to 35% of babies exposed to it: Isotretinoin (Accutane®)
Women, who are prescribed Isotretinoin have to sign a pledge to not become pregnant while taking the drug.
It is so toxic, that people are not allowed to donate blood while taking isotretinoin and up to a month afterwards:
So what did eating liver do to the levels of isotretinoin?
The study showed that eating liver increased the levels of isotretinoin more than 22-fold.
The baseline concentration of isotretinoin among the study participants was at around 1.4 ng/ml. Those were the average isotretinoin levels BEFORE they were given either vitamin A supplements or liver.
After the consumption of 50 mg (150 mg) of calf liver those levels increased 10-fold (more than 22-fold).
They went from an average of 1.4 ng/ml to 14 ng/ml and 31 ng/ml, respectively.
The overall exposure to isotretinoin reached a whopping 243 ng*h/ml (596 ng*h/ml).
[Supplementation with 50 mg (150 mg) of vitamin A caused an even higher overall exposure to isotretinoin of 359 ng*h/ml (674 ng*h/ml).]
The results of the study show that eating liver causes a SIGNIFICANT increase in isotretinoin and other known teratogenic metabolites of retinol.
The study authors wrongly discounted the dangers of eating liver because they were making wrong assumptions about the toxicities of the retinol metabolites.
In fact, at one point in the study, the authors admit that there is a possible risk of incurring birth defects from eating liver by writing:
"Even allowing for the 8-20 fold differences in all-trans-retinoic acid formation from supplements compared with liver, the foetal exposure after the consumption of large amounts of liver could theoretically approach those in women who produced malformed babies while taking vitamin supplements."
