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Truths about Vitamin A and Toxicity from Foods - The Science with Dr. Garrett Smith - Part 1
Nutrition with Judy
Overview
This video challenges the common belief that natural forms of Vitamin A from food are inherently safe and cannot lead to toxicity. Dr. Garrett Smith explains that both natural (from foods like liver) and synthetic Vitamin A are processed similarly by the body and can cause toxicity if consumed in excess. He highlights that serum retinol levels don't accurately reflect liver stores and that even moderate intakes of Vitamin A-rich foods can be problematic for some individuals, especially pregnant women and children. The discussion emphasizes that quantity, not just source, is the critical factor in Vitamin A toxicity, and individual tolerance varies significantly.
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Chapters
- Carotenoids from plants are not essential for human health.
- Beta-carotene is converted into retinaldehyde, a form of Vitamin A that can be considered toxic due to its aldehyde structure.
- Retinol, the common form of Vitamin A measured in blood, requires binding to retinol-binding protein to prevent toxicity.
- Free retinol in the blood is toxic and a cause of hypervitaminosis A.
- Dietary Vitamin A, regardless of source (natural or synthetic), is metabolized into various retinoic acids, some of which are identical to pharmaceutical compounds like Accutane.
Understanding the different forms of Vitamin A and how the body processes them is crucial for recognizing potential risks, especially when considering dietary intake and supplementation.
Retinoic acids, formed from dietary Vitamin A, are chemically identical to pharmaceutical drugs like Accutane (13-cis retinoic acid) and Retin-A (all-trans retinoic acid).
- Animal-based Vitamin A, consumed from foods like liver, eggs, and dairy, is primarily in the form of retinol esters.
- Retinol esters are retinol bound to a fatty acid, with retinol palmitate being a common form.
- The liver is a significant storage site for Vitamin A, and this storage is not necessarily for later use but can indicate the liver's inability to process or excrete it quickly enough.
- Consuming palmitic acid, a common fatty acid in animal foods, can increase the body's production and storage of retinol palmitate in the liver.
This explains why consuming Vitamin A-rich animal foods can lead to high body stores, and why focusing solely on blood levels can be misleading regarding overall Vitamin A status.
Beef liver is composed of about 94% retinol esters and 6% retinol, with retinol palmitate making up roughly two-thirds of the stored retinol esters in human and animal livers.
- Scientific research, including studies from 1958, indicates that synthetic Vitamin A produces the same toxic effects as naturally occurring Vitamin A from sources like fish oil concentrates.
- Animal studies consistently show that livers rich in Vitamin A, liver oils, and purified Vitamin A preparations cause identical toxic effects when given in equivalent amounts.
- The toxicity observed in animal studies was directly linked to the Vitamin A content itself, not other components of the natural sources.
- Excess Vitamin A, whether from natural or synthetic sources, has been shown to be toxic in various animal species, including rats, mice, guinea pigs, rabbits, and cockerels.
This challenges the notion that natural Vitamin A is inherently safer than synthetic forms, suggesting that the body processes them similarly regarding toxicity.
A book of studies by Rhoden demonstrated that excess pure crystalline vitamin A alcohol and acetate produced the same toxic effects in rats as natural sources of vitamin A.
- Increasing retinol intake, even from dietary and supplement sources combined, is negatively associated with skeletal health (bone mineral density) in the elderly.
- Negative effects on bone mineral density were observed at intakes not far beyond the Recommended Daily Allowance (RDA), particularly in supplement users.
- An ounce of beef liver can contain significantly more Vitamin A (around 4700 IU) than recommended daily allowances for young children, potentially leading to toxicity.
- Government agencies have lowered the RDA for Vitamin A and made its labeling optional on foods, which may obscure potential intake issues.
This highlights that even seemingly moderate consumption of Vitamin A-rich foods can exceed safe levels for certain populations, impacting bone health and potentially other systems.
The Rancho Bernardo study found that intakes of Vitamin A around 5,000 IU per day were associated with decreased bone mineral density, a level easily reached by consuming just one ounce of beef liver.
- It is possible to become toxic from Vitamin A found in foods, not just supplements.
- Even carotenoids, like those in carrots, can lead to toxicity. Rabbits fed only carrots developed joint disease, and a human case ('Carrot Man') experienced liver problems and skin discoloration from excessive carrot consumption.
- A woman developed Vitamin A poisoning and liver injury from a diet high in liver, yellow-green vegetables, and seaweed.
- Numerous case studies document toxicity in both animals (rats, cats, cheetahs, dogs) and humans from consuming various animal livers (polar bear, beef, pork, fish, shark, chicken) and even fish liver.
This provides concrete evidence that toxicity is not limited to supplements and can arise from consuming Vitamin A-rich foods, challenging the assumption that 'food is always safe'.
A two-year-old boy died from chicken liver spread, his younger brother became very ill, while their sister showed no ill effects, demonstrating significant individual variation in tolerance.
- There is significant individual variation in how much Vitamin A a person can tolerate, influenced by genetics, nutrient status, and liver function.
- Men generally process liver-related functions faster than women due to hormonal differences.
- The 'duration paradox' describes how substances like Vitamin A can appear beneficial in the short term (e.g., improving acne) but lead to negative long-term consequences.
- Short-term improvements seen with Vitamin A or its derivatives may be due to speeding up cellular processes, but this can lead to burnout and long-term issues.
- Even when reducing Vitamin A intake, blood levels might not immediately drop and can even temporarily increase as stored Vitamin A is released from the liver.
This explains why some people react differently to Vitamin A-rich foods and why initial perceived benefits might mask underlying toxicity that develops over time.
Caffeine and Viagra are cited as examples of the 'duration paradox,' where they provide short-term benefits but can lead to tolerance, dependency, or adverse effects with prolonged use.
- Individuals with existing liver problems or impaired liver function process Vitamin A more slowly, increasing their risk of toxicity even with lower intakes.
- Subclinical liver congestion or cholestasis can impair Vitamin A processing without being detectable by standard medical tests.
- Damage to the liver from various sources (medications, toxins) can exacerbate Vitamin A processing issues.
- The body may slow down or stop detox pathways if Vitamin A levels in the blood are already high, to prevent further accumulation in the bloodstream.
- Stored Vitamin A in the liver can last for years (potentially up to 10 years), meaning that reducing intake doesn't immediately deplete stores.
This emphasizes the critical role of liver health in managing Vitamin A levels and highlights why individuals with compromised liver function are particularly vulnerable to toxicity.
A man taking 50,000 IU of Vitamin A daily had low blood levels (18 IU/mL), but after stopping supplementation and reducing intake, his blood levels rose to 62 IU/mL around week 12, indicating release from liver stores.
Key takeaways
- Both natural (food-based) and synthetic Vitamin A are processed similarly by the body and carry the same risk of toxicity.
- Serum Vitamin A levels are poor indicators of stored Vitamin A in the liver; toxicity can exist even with normal or low blood levels.
- Excessive consumption of Vitamin A-rich foods like liver, even in moderate amounts over time, can lead to toxicity.
- Individual tolerance to Vitamin A varies greatly, meaning what is safe for one person can be toxic for another.
- Pregnant women and young children are particularly vulnerable to Vitamin A toxicity, with strict limits recommended.
- Carotenoids from vegetables, while not essential, can also contribute to Vitamin A toxicity if consumed in very large quantities.
- Long-term health issues can arise from Vitamin A, even if short-term effects appear beneficial (the 'duration paradox').
- Liver health is crucial for processing Vitamin A; impaired liver function increases the risk of toxicity.
Key terms
RetinolRetinaldehydeRetinoic AcidRetinol EstersRetinol PalmitateHypervitaminosis ACarotenoidsBeta-caroteneRecommended Daily Allowance (RDA)Duration ParadoxLiver Storage
Test your understanding
- Why is it inaccurate to assume that natural Vitamin A from food sources is always safe and cannot cause toxicity?
- How do serum retinol levels differ from liver stores of Vitamin A, and why is this distinction important for understanding toxicity?
- What is the 'duration paradox,' and how does it apply to Vitamin A consumption?
- Explain why individual tolerance to Vitamin A varies so significantly, and what factors might influence this variation?
- What are the specific risks associated with Vitamin A toxicity for pregnant women and young children, according to the video?