Vitamin E: A Closer Look at Tocotrienols

Oct 17, 2017
Volume: 
20
Issue: 
8

By Barrie Tan, PhD, American River Nutrition

 

Researchers estimate that the human body could contain as many as 75 trillion cells. Each of those cells is surrounded by a bean-shaped membrane made up of dense rows of fatty acids that require protection from lipid peroxidation. Of the many popular antioxidants that help protect cells (e.g., astaxanthin, lutein, lycopene, CoQ10), vitamin E is the one nature chose to reside within the lipid cell membrane to protect its integrity. Vitamin E comes in the perfect molecular shape to do this job—like a tadpole, with a head and tail, similar to the phospholipids that complement the cell membrane. Vitamin E is distinguished by a chromanol head with a lipid-soluble side chain. 

There are two forms of vitamin E: tocotrienols and tocopherols. Not all forms of vitamin E are the same, however. Tocopherols have a longer tail (phytyl), whereas tocotrienols have a shorter, more flexible tail (farnesyl).1 This small difference in molecular structure allows tocotrienols to cover a larger surface area of the cell membrane more quickly, hence making them more effective as antioxidants. As this article will discuss, an expanding body of research points to significant benefits supporting the tocotrienol form. 

 

Tocotrienols vs. Tocopherols 

When vitamin E was discovered in 1922, it was discovered as alpha-tocopherol. Between that time and 1940, scientists delved into tocopherol research, ranging from alpha-tocopherol’s isolation from plants2, chemical identification3,4, complete synthesis5, and antioxidant activity6. In fact, the tocopherol form remained the main focus of vitamin E science for decades, and, as such, research on tocopherols boomed.7,8

Tocotrienols were discovered later, in the mid-1960s.9,10 Tocotrienols’ ability to lower lipids was first reported in the early 1980s; in the 1990s, tocotrienols were associated with reduction of cardiovascular diseases and inhibition of cancers.11 Despite the growing research on tocotrienols, they are still often confused with tocopherols and were not even properly listed in the Merck Index, the encyclopedia of chemicals, drugs, and biologicals, until 2001.12

Lingering confusion over the difference between tocotrienols and tocopherols is understandable, considering that both have the same chromanol head. Today, alpha-tocopherol remains the most common vitamin E source on the market despite some lingering debate around it. 

 

Debate around Tocopherols

Commercialization of natural, soy-derived tocopherols began in the 1950s; however, high demand for tocopherols prompted many companies to eventually switch from soy- and corn-derived tocopherols (whose crops typically yielded less than 20% alpha-tocopherol) to 100% alpha-tocopherol. Today, much of the “natural” alpha-tocopherol on the market is in fact semi-synthetic, with soy- and corn-based tocopherols synthesized to (RRR- or d-) alpha-tocopherol via the addition of one methyl group to gamma-tocopherol and two methyl groups to delta-tocopherol.13

While synthetic tocopherol ingredients do exist in the market, synthetic tocotrienol ingredients do not. Tocotrienols are still sourced from a wide array of foods, including wheat, barley, and corn. Rice, palm, and annatto are the richest tocotrienol sources. 

Some research suggests that alpha-tocopherol interferes with the helpful activity of tocotrienols. Following an animal study published in the Journal of Nutrition in 199614, researchers suggested that tocotrienols were more potent hypocholesterolemic agents when administered with the lowest alpha-tocopherol content possible. In the study, chickens were fed either an alpha-tocopherol control diet or alpha-tocopherol administered in combination with gamma-tocotrienol. The group with the largest-supplemented amount of alpha-tocopherol showed increased activity of the rate-limiting enzyme responsible for cholesterol production, 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), and as a result cholesterol levels rose in that group—prompting researchers to conclude that in order for tocotrienols to help lower cholesterol, alpha-tocopherol content should not be more than 15%. 

Four years later, another study in guinea pigs reported similar findings in favor of tocotrienols compared to tocopherols.15 In this study, researchers found that alpha-tocopherol, when co-administered with tocotrienols, reduced tocotrienols’ inhibitory effect on HMGR. When administered alone, tocotrienols reduced the enzyme’s activity by 48%; however, adding alpha-tocopherol meant that the combination inhibited HMGR by only 13%. Fast-forward through 15 years of clinical studies: tocopherol-tocotrienol mixtures did little or nothing to lower lipids, but when tocopherols were removed from the mixtures, lipids would decrease.16, 17

Additional research suggests that tocopherols may be a monkey-wrench to tocotrienol functions. One small 2009 prospective study indicated that tocopherols may interfere with breast cancer medication18, while a 2015 animal study19 found that excessive amounts of alpha-tocopherol may worsen stroke-related brain injuries. In 2005, those same researchers found that while orally supplemented alpha-tocotrienol was shown to reach most tissues and vital organs (including the skin, adipose tissue, ovaries, heart, liver, central nervous system, spinal cord, brain, lung, testes, and skeletal muscle), the mechanisms for transporting alpha-tocopherol and alpha-tocotrienol apparently compete, leading the researchers to note that “the transport efficiency of alpha-tocotrienol to tissues may be maximized by eliminating the co-presence of alpha-tocopherol in the oral supplement.”20

The reasoning behind this can be readily understood. Of all eight isomers of vitamin E, only alpha-tocopherol has a known transport protein—a protein chaperone that provides a rite of passage—that recognizes alpha-tocopherol alone of all the eight isomers and delivers it to the tissues of interest. Then, by passive diffusion and emulsification with fats in a meal, all other vitamin E isomers get absorbed, like most lipid-soluble nutrients. Thus, co-supplementation with alpha-tocopherol is likely to compromise tissue delivery of alpha-tocotrienol.21 Alpha-tocopherol administration has also been found to decrease the gamma-tocotrienol concentration in the adipose tissue and skin, inhibiting both alpha-tocotrienol and gamma-tocotrienol tissue uptake.22

References: 
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  2. Evans HM et al., “The isolation from wheat germ oil of an alcohol alpha-tocopherol, having the properties of vitamin E,” The Journal of Biological Chemistry, vol. 113, no. 1 (February 1936): 319-332
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