How Two Researchers Proved Fat Is Essential In 1929 — The Discovery Behind Omega-3
Quick Read In 1929, researchers discovered that certain fats are essential, meaning your body cannot make them and must get
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Simon Parrott – Vitacuity Ltd
Vitamin E comes in two forms with very different molecular shapes. Natural vitamin E (labeled d-alpha-tocopherol) has one specific shape that your body recognizes and uses. Synthetic vitamin E (labeled dl-alpha-tocopherol) is a mixture of eight different shapes, and your liver strongly prefers the natural form. This means roughly half of synthetic vitamin E may not be properly utilized by your body.
Research across animal studies and limited human trials shows natural vitamin E is significantly better absorbed and reaches tissues more effectively. A human study of nursing mothers found natural vitamin E increased breast milk levels by 57 percent, compared to 39 percent for synthetic. Even more striking, the placenta appears to actively filter out synthetic forms and preferentially passes natural vitamin E to developing babies.
The practical takeaway: check your supplement label for “d-alpha-tocopherol” (natural) versus “dl-alpha-tocopherol” (synthetic). The difference is substantial enough that choosing natural form is worthwhile, especially during pregnancy. You don’t need higher doses of natural vitamin E to get better results than synthetic at the same dose.
Verdict: Natural vitamin E (d-alpha-tocopherol) is meaningfully better absorbed and utilized by your body than synthetic (dl-alpha-tocopherol), making it the preferable choice when selecting a supplement.
Here’s a question most people never think to ask when they pick up a vitamin E supplement: is all vitamin E actually the same? The bottle says “vitamin E.” The dosage looks identical. The price might even be cheaper. So why would the form matter? The truth is, it matters quite a lot, and the reason comes down to something most supplement labels don’t bother to explain: molecular geometry. Natural and synthetic vitamin E are made from the same building blocks, but they’re assembled in fundamentally different shapes. And your body, it turns out, is surprisingly choosy about which shapes it will actually use.
Vitacuity has reviewed over 1.77 million research papers and selected the most relevant studies on this topic. What the evidence shows is genuinely interesting, and if you’re currently taking a vitamin E supplement, there’s a reasonable chance you’re taking the synthetic form without knowing it.
Vitamin E is not a single molecule. It’s a family of compounds, and the most biologically active member is called alpha-tocopherol. But here’s where it gets interesting: alpha-tocopherol has three points on its molecular structure, called chiral centres, where the molecule can bend one of two ways. In chemistry, those two orientations are called R (from the Latin *rectus*, meaning right) and S (*sinister*, meaning left).
Natural vitamin E, found in foods like sunflower seeds, almonds and wheat germ oil, contains only one specific configuration at all three of those chiral centres: RRR-alpha-tocopherol. That’s the only form nature produces [3].
Synthetic vitamin E, on the other hand, is made through a chemical process that can’t control which way each of those three centres folds. The result is an equal mixture of all eight possible stereoisomers, RRR, RRS, RSR, RSS, SRR, SSR, SRS and SSS, collectively called all-rac-alpha-tocopherol (you might see it on labels as “dl-alpha-tocopherol”) [3].
On paper, those eight stereoisomers might look similar. In the body, they behave very differently.
Your liver contains a protein called alpha-tocopherol transfer protein (alpha-TTP). Its job is to selectively package alpha-tocopherol for distribution around the body. And it strongly prefers the RRR form, the natural one. The 2S stereoisomers (SSS, SSR, SRS, SRR) are essentially not recognised by this protein and have very low bioavailability [3]. That means if you take synthetic vitamin E, roughly half of what you’ve swallowed may simply not be utilised the way you’d hope.
On supplement labels: – d-alpha-tocopherol = natural (RRR form only) – dl-alpha-tocopherol = synthetic (all eight stereoisomers)
The “l” in “dl” is the giveaway.
For decades, the supplement industry used a conversion factor of 1.36:1 to account for the difference in potency between natural and synthetic vitamin E, meaning that 1 IU of natural vitamin E was considered equivalent to 1.36 IU of synthetic. This ratio was established using an old rat-based test called the resorption-gestation test.
More recent research suggests this ratio significantly underestimates the real-world difference.
A comprehensive review published in the *Journal of the Science of Food and Agriculture* (2010) critically examined the methodologies used to determine this ratio [9]. The review found that a major source of conflicting results in the literature was a failure to account for vitamin E already present in the animals’ diets before testing began, a confounding factor that artificially compressed the apparent difference between natural and synthetic forms. When studies properly controlled for baseline vitamin E status, the evidence pointed toward a real-world bioavailability ratio closer to 2:1 in favour of natural vitamin E [3][9].
Put plainly: a supplement labelled “400 IU” of synthetic vitamin E may only deliver the functional equivalent of around 200 IU of the natural form, and possibly less, once your body has filtered out the stereoisomers it can’t use.
*Evidence grade: Promising, supported by multiple animal studies and one systematic methodological review; human trial data on the 2:1 ratio is limited.*
It’s one thing to measure vitamin E levels in the blood. It’s another to ask whether it reaches the tissues that matter, heart, brain, liver, muscle. A 2009 animal study published in the *Journal of Animal Science* examined this in pigs [5].
Twenty-four finishing gilts were divided into groups receiving either 22 mg/kg of synthetic vitamin E acetate or varying doses of natural vitamin E acetate (ranging from 6.71 to 16.18 mg/kg). After 32 days, tissue samples from heart, kidney, spleen, liver, lung and adipose were analysed.
The results were striking. Pigs fed just 8.33 mg/kg of natural vitamin E, less than 40% of the synthetic dose, showed higher alpha-tocopherol concentrations in spleen, loin and adipose tissue than pigs fed 22 mg/kg of synthetic. At 16.18 mg/kg of natural, still well under the synthetic dose, levels were significantly higher across six tissues including heart and liver [5].
A parallel study in lambs (published in *Animal*, 2019) added further nuance [6]. Researchers found that the bioavailability advantage of natural over synthetic vitamin E was dose- and tissue-dependent, with the liver retaining a disproportionate amount of the 2S synthetic stereoisomers (up to 35–39% of total alpha-tocopherol in the liver), while muscle, heart and spleen showed much lower retention of these less bioactive forms [6]. The conclusion: no single conversion ratio can capture the complexity of how these forms behave differently across different tissues.
*Evidence grade: Promising, consistent findings across multiple animal species; human tissue-level data is limited.*
Moving to human data, a 2015 randomised controlled trial published in the *Journal of Pediatric Gastroenterology and Nutrition* examined 109 healthy lactating women in Brazil [13]. Women were randomised into three groups: no supplementation, natural alpha-tocopherol supplementation, or synthetic alpha-tocopherol supplementation.
Blood and colostrum samples were collected before and after supplementation.
The findings: women who received the natural form showed a 57% increase in alpha-tocopherol concentration in colostrum. Women receiving the synthetic form showed a 39% increase. Both beat the control group, but natural vitamin E was clearly more effective at raising the vitamin E content of breast milk [13].
This matters because newborns are considered a high-risk group for vitamin E deficiency, and colostrum is one of their primary sources of the vitamin in the days after birth.
*Evidence grade: Promising, one RCT in 109 human subjects; single population (Brazilian), single time point, short duration.*
Perhaps the most revealing piece of human evidence comes from a 2021 study published in *Current Developments in Nutrition*, which examined 66 maternal-umbilical cord plasma pairs from a racially diverse population in the United States [15].
Researchers measured the stereoisomer profile of alpha-tocopherol in both maternal blood (at 16 and 28 weeks of gestation) and cord blood at birth. The key question: does the placenta pass both natural and synthetic stereoisomers equally to the baby?
The answer was no. Cord plasma had a significantly higher proportion of RRR-alpha-tocopherol than maternal plasma (p < 0.05), and a significantly lower proportion of synthetic (2S) stereoisomers (p < 0.0001) [15].
In other words, the placenta appears to act as a biological filter, preferentially transferring the natural form to the developing baby while holding back the synthetic stereoisomers.
Critically, the study also found that higher maternal levels of synthetic vitamin E were positively correlated with higher cord levels of synthetic vitamin E (r = 0.538, p < 0.00001), and negatively correlated with the proportion of natural RRR-alpha-tocopherol in neonatal circulation [15]. Higher synthetic vitamin E intake by the mother was associated with a less favourable stereoisomer profile in the newborn.
The researchers rightly called for further research to understand what this means for neonatal health, but the implication is significant. The human body, from the earliest stages of life, seems to distinguish between these molecular forms in ways that matter.
*Evidence grade: Promising, well-designed observational study in 66 human maternal-fetal pairs; causality not established, correlation only.*
One area of research that is still early stage but genuinely interesting is the question of whether natural and synthetic vitamin E differ not just in how well they’re absorbed, but in what they do once they’re inside cells.
A 2010 mouse study published in *Archives of Biochemistry and Biophysics* examined gene expression in T lymphocytes (immune cells) from mice supplemented with either natural or synthetic vitamin E [7]. Using gene array experiments, researchers found “significant qualitative and quantitative differences” between the two forms in how they regulated gene expression in response to immune cell stimulation. Unique genetic markers were identified for each form, meaning the two types of vitamin E were not simply equivalent doses; they were producing distinct biological effects at the cellular level [7].
This is early-stage science, mouse studies, not human trials, and we shouldn’t overinterpret it. But it raises an important question: are we measuring the right things when we compare natural and synthetic vitamin E? Bioavailability is only part of the story. What the vitamin does once absorbed may also differ.
*Evidence grade: Early stage, mouse study only; human gene expression research needed before conclusions can be drawn.*
A 2020 study published in the *Journal of Equine Veterinary Science* examined 18 horses over a 6-week training protocol, comparing synthetic vitamin E at low dose (1,000 IU/day), synthetic at high dose (4,000 IU/day), and natural vitamin E at 4,000 IU/day [8].
Horses fed natural vitamin E showed: – Higher serum alpha-tocopherol levels throughout (p < 0.05) - Lower oxidative stress markers (thiobarbituric acid-reactive substances) compared to low-dose synthetic (p = 0.02) – Lower muscle enzyme levels (aspartate aminotransferase) after exercise compared to both synthetic groups (p = 0.02), suggesting less exercise-induced muscle damage – Better functional performance, less reduction in stride duration after exercise (p = 0.02) – Lower TNF-alpha expression (an inflammatory marker) compared to high-dose synthetic (p = 0.01) [8]
This is an animal study, and extrapolating directly to humans requires caution. But it’s notable that the natural form outperformed not just the low-dose synthetic, but also the same dose of synthetic, suggesting it isn’t simply a matter of how much reaches the bloodstream, but potentially how the different stereoisomers behave once absorbed.
*Evidence grade: Early stage for human application, well-controlled animal study with functional outcomes; human exercise trials needed.*
Honest transparency is part of how we operate at Vitacuity, so let’s be clear about the limits of what this research tells us.
The 2:1 bioavailability ratio is not definitively established in humans. Most of the compelling evidence comes from animal studies, pigs, horses, lambs, rats. Human data is more limited, and the much-cited original ratio of 1.36:1 was itself derived from animal testing. The truth likely lies somewhere in between, and it probably varies depending on the tissue, the dose, and the individual.
Conflicted results exist. One 1999 human study in healthy male subjects found no significant difference in serum alpha-tocopherol levels between natural and synthetic forms when doses were matched by IU [2]. This matters, it suggests that at certain doses, and in certain populations, the functional difference may be smaller than some studies suggest. The likely explanation, supported by the 2010 methodological review [9], is that baseline vitamin E status significantly affects how differences between forms are measured. When someone is replete in vitamin E, the marginal difference between forms may be harder to detect. When someone is deficient or stressed, the difference becomes more apparent.
The long-term health implications are unclear. We don’t have large-scale, long-duration human RCTs examining whether people who supplement with natural vitamin E have meaningfully better health outcomes than those taking synthetic, fewer cardiovascular events, slower cognitive decline, lower cancer risk. That evidence simply doesn’t exist yet.
The gene expression differences are intriguing but unproven in humans. The mouse data showing different cellular responses to natural versus synthetic vitamin E [7] is genuinely interesting but requires human replication before we can draw practical conclusions.
The placenta findings need follow-up. The 2021 human study showing preferential placental transfer of RRR-alpha-tocopherol [15] is important, but it’s observational, and we don’t yet know whether the lower proportion of natural vitamin E in some neonates has measurable health consequences.
So where does all this leave you?
First, the practical reality: vitamin E is fat-soluble, which means, unlike vitamin C or the B vitamins, excess doesn’t simply wash out in your urine. Fat-soluble vitamins accumulate. That said, vitamin E has a low toxicity profile at normal supplemental doses, and serious adverse effects have only been reported at sustained very high doses. At the kinds of levels found in quality supplements (typically 67–268 mg, or 100–400 IU), the risk of supplementing is genuinely low.
Here’s what a sensible, well-informed person would do with this research:
Check your label first. Turn over your vitamin E supplement. If it says “dl-alpha-tocopherol”, that’s synthetic. If it says “d-alpha-tocopherol”, that’s natural. This one letter is the most important thing on the label. Many cheaper multivitamins and standalone vitamin E supplements use the synthetic form because it’s significantly cheaper to manufacture.
Opt for natural (d-alpha-tocopherol) where practical. The weight of evidence, across multiple animal species and the available human data, consistently shows that the natural RRR form is better absorbed, better retained in tissues, and may behave differently at a cellular level. The human RCT in lactating mothers showed a meaningful difference in real-world outcomes [13]. The placenta study suggests the body itself filters for the natural form [15]. That’s a consistent signal across diverse research.
Don’t obsess over dosage if you’re switching forms. If you were taking 400 IU of synthetic and want to switch to natural, the existing evidence suggests you’re likely getting a better-utilised dose even at a lower IU, so a quality supplement in the 100–200 mg range (roughly 150–300 IU) of natural d-alpha-tocopherol is a sensible place to be.
You don’t need to test your vitamin E levels before supplementing. Blood testing for vitamin E exists but is rarely done in routine UK healthcare and isn’t practically accessible for most people. Given the low toxicity risk at normal doses, the cost-benefit of simply switching to a natural form supplement is clearly favourable for most adults.
Consider the wider picture. The research on vitamin E and brain health, cardiovascular protection and immune function is broader than this article covers, but getting the form right is the foundation. There’s little point optimising dose if a significant fraction of what you’re taking isn’t being utilised.
One practical note: if you are pregnant or planning to become pregnant, the 2021 human study [15] and the rat data [1][4] both suggest that synthetic vitamin E from the mother may reduce the proportion of bioactive RRR-alpha-tocopherol available to the developing baby. Given that the natural form is available at comparable cost and the potential consequence is meaningful, the case for choosing natural during pregnancy is strong, even if the human evidence isn’t yet definitive.
The bottom line: the “d” versus “dl” distinction on a label is not marketing fluff. It’s a meaningful molecular difference that your body recognises, your liver processes differently, and your placenta actively filters. For the cost of checking the label, you could be getting significantly more from every capsule you take.
[1] Natural Vitamin E Supplementation during Pregnancy in Rats Increases RRR-α-Tocopherol Stereoisomer Proportion and Enhances Fetal Antioxidant Capacity, Compared to Synthetic Vitamin E Administration. (2023). https://pubmed.ncbi.nlm.nih.gov/36702104/
[2] Relative bioavailabilities of natural and synthetic vitamin E formulations containing mixed tocopherols in human subjects. (1999). DOI: 10.1024/0300-9831.69.2.92 | https://pubmed.ncbi.nlm.nih.gov/10218145/
[3] Utilization of stereoisomers from alpha-tocopherol in livestock animals. (2010). DOI: 10.1111/j.1439-0396.2009.00924.x | https://pubmed.ncbi.nlm.nih.gov/19663978/
[4] Natural Vitamin E Supplementation during Pregnancy in Rats Increases RRR-α-Tocopherol Stereoisomer Proportion and Enhances Fetal Antioxidant Capacity, Compared to Synthetic Vitamin E Administration. (2023). https://pubmed.ncbi.nlm.nih.gov/36702104/
[5] Effect of vitamin E source, natural versus synthetic, and quantity on serum and tissue alpha-tocopherol concentrations in finishing swine. (2009). DOI: 10.2527/jas.2008-1570 | https://pubmed.ncbi.nlm.nih.gov/19717777/
[6] Bioavailability of RRR- and all-rac-α-tocopheryl acetate in lambs. (2019). DOI: 10.1017/S1751731118003373 | https://pubmed.ncbi.nlm.nih.gov/30587272/
[7] Differential effects of natural and synthetic vitamin E on gene transcription in murine T lymphocytes. (2010). DOI: 10.1016/j.abb.2009.12.015 | https://pubmed.ncbi.nlm.nih.gov/20026030/
[8] Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses. (2020). DOI: 10.1016/j.jevs.2020.103103 | https://pubmed.ncbi.nlm.nih.gov/32684249/
[9] A critical review of methodologies used in determination of relative bio-availability ratio of RRR-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate. (2010). DOI: 10.1002/jsfa.3994 | https://pubmed.ncbi.nlm.nih.gov/20564451/
[10] Effects of natural (RRR alpha-tocopherol acetate) or synthetic (all-rac alpha-tocopherol acetate) vitamin E supplementation on reproductive efficiency in beef cows. (2010). DOI: 10.2527/jas.2009-1807 | https://pubmed.ncbi.nlm.nih.gov/20495121/
[11] Effects of oral micellized natural vitamin E (D-α-tocopherol) v. synthetic vitamin E (DL-α-tocopherol) in feed on α-tocopherol levels, stereoisomer distribution, oxidative stress and the immune response in piglets. (2014). https://pubmed.ncbi.nlm.nih.gov/24534689/
[12] A Comparison of Natural (D-α-tocopherol) and Synthetic (DL-α-tocopherol Acetate) Vitamin E Supplementation on the Growth Performance, Meat Quality and Oxidative Status of Broilers. (2016). https://pubmed.ncbi.nlm.nih.gov/26954216/
[13] Maternal supplementation with natural or synthetic vitamin E and its levels in human colostrum. (2015). DOI: 10.1097/MPG.0000000000000635 | https://pubmed.ncbi.nlm.nih.gov/25419678/
[14] Distinction of synthetic dl-α-tocopherol from natural vitamin E (d-α-tocopherol) by reversed-phase liquid chromatography. (2016). https://pubmed.ncbi.nlm.nih.gov/27157422/
[15] α-Tocopherol Stereoisomer Profiles in Matched Human Maternal and Umbilical Cord Plasma. (2021). DOI: 10.1093/cdn/nzab073 | https://pubmed.ncbi.nlm.nih.gov/34104848/ | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8178107/
This article is for informational purposes only and does not constitute medical advice. Food supplements should not be used as a substitute for a varied and balanced diet and healthy lifestyle. If you are pregnant, breastfeeding, taking medication or have a medical condition, consult your doctor before taking any supplement. These statements have not been evaluated by the Food and Drug Administration (FDA) or the Medicines and Healthcare products Regulatory Agency (MHRA). This product is not intended to diagnose, treat, cure, or prevent any disease.
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