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Myth: Serum Retinol is not a useful measurement of subclinical VA toxicity
Yeah, I think your summary is about right. Regarding the 4,000 per day, we have to be careful because this study uses IU, not mcg RAE. And there's some complexity in the conversion factor because 1,000 IU from plant sources isn't the same in RAE as 1,000 IU from liver.
I think the conversion factors are as follows:
| Source / Form of Vitamin A [1, 2] | Calculation Formula |
|---|---|
| Retinol (Animal sources, preformed Vitamin A) Beta-carotene (Supplements) |
mcg RAE = IU × 0.30 |
| Beta-carotene (Dietary sources from food) | mcg RAE = IU × 0.05 |
| Alpha-carotene or Beta-cryptoxanthin (Dietary sources) | mcg RAE = IU × 0.025 |
So if his 4,000 IU per day was all coming from vegetables, it would be like 4,000 * 0.05 = 200 mcg RAE. So his daily intake was only 200 mcg RAE. And the literature seems to agree that plant sources don't contribute to toxicity as much as animal sources, because the body can regulate to some degree how much beta-carotene is absorbed in the intestines, and then how much is converted once absorbed into the body.
In practical terms, my approach is that I generally play things by ear, and see how my body responds to different foods. I think Grant's suggested target of 10% the RDA is a pretty good starting point. If you try going far below the 10% RDA and find that it makes you feel worse, I wouldn't force yourself to go that low.
Getting labs is fine if you want, but you may also want to assess RBP (retinol binding protein), since I think the RBP level helps give a sense of how much capacity the body has to safely transport or sequester vitamin A outside the liver.
Also, the study reports that the guy in the study was releasing vitamin A from his liver at a pretty fast rate, 226,000 IU per day.
Per Claude AI:
This is stored hepatic vitamin A — retinyl esters, i.e. preformed, so × 0.3 (no carotene ambiguity here):
226,000 IU × 0.3 = 67,800 µg RAE/day ≈ 68 mg/day
That's about 75× the RDA (~900 µg) and 23× the 3,000 µg preformed UL being cleared from his liver daily. The store it drained from was enormous: at the second biopsy his liver held 19,700 IU/g × 1,500 g ≈ 29.5 million IU ≈ 8.9 g RAE, versus a normal whole-liver store of ~0.05–0.3 g — roughly 30–200× normal. So he shed about 0.068 g/day, under 1% of the store, consistent with their slow ~58-day turnover.
Quote from Navid on June 30, 2026, 7:55 amYeah, I think your summary is about right. Regarding the 4,000 per day, we have to be careful because this study uses IU, not mcg RAE. And there's some complexity in the conversion factor because 1,000 IU from plant sources isn't the same in RAE as 1,000 IU from liver.
I think the conversion factors are as follows:
Source / Form of Vitamin A [1, 2] Calculation Formula Retinol (Animal sources, preformed Vitamin A)
Beta-carotene (Supplements)mcg RAE = IU × 0.30 Beta-carotene (Dietary sources from food) mcg RAE = IU × 0.05 Alpha-carotene or Beta-cryptoxanthin (Dietary sources) mcg RAE = IU × 0.025
So if his 4,000 IU per day was all coming from vegetables, it would be like 4,000 * 0.05 = 200 mcg RAE. So his daily intake was only 200 mcg RAE. And the literature seems to agree that plant sources don't contribute to toxicity as much as animal sources, because the body can regulate to some degree how much beta-carotene is absorbed in the intestines, and then how much is converted once absorbed into the body.
In practical terms, my approach is that I generally play things by ear, and see how my body responds to different foods. I think Grant's suggested target of 10% the RDA is a pretty good starting point. If you try going far below the 10% RDA and find that it makes you feel worse, I wouldn't force yourself to go that low.
Getting labs is fine if you want, but you may also want to assess RBP (retinol binding protein), since I think the RBP level helps give a sense of how much capacity the body has to safely transport or sequester vitamin A outside the liver.
Yeah, I do feel best when I am about 150 - 200 mcg per day (not entirely sure that is low enough to get this crap out of my body, but going lower and I feel like trash). That about lines up with what you're saying about that fellow's intake.
I also ran another lab this morning, just to see if my serum has fallen from 74 mcg/dl at the first of the month.
Fingers crossed.