A Bit on That Shampoo Vitamin

Apart from the well-known vitamins like vitamin C and vitamin D, there are others that are only known in context or perhaps not known at all. Take vitamin K for example. Did you even know there was such a thing? If it weren’t for its bizarre role in blood clotting, I wouldn’t have either. Another one most people only know a bit about is vitamin E. I most associate this vitamin with shampoo because a number of soaps advertise its antioxidant properties as the secret to model-like hair. But questionable advertisement schemes aside, vitamin E does play roles in human health so let’s learn a little about it, shall we?

Though it sounds singular, vitamin E is actually a class of eight fat-soluble antioxidant compounds, all of which contain a chromane ring with a 2-hydrophobic side chain (four compounds with saturated side chains (tocopherols), three with trans double bonds (tocotrienols)) and a 6-hydroxyl group. Varying positions of methyl functional groups around the phenyl portion of the chromane ring is what separates the alpha-, beta-, gamma- and delta-tocopherols as well as the tocotrienol subtypes. 

Fig. 1: Vitamin E subtypes with sidegroup key (American Oil Chemists' Society)

All vitamin E forms exhibit antioxidant properties due to the 6-hydroxyl group’s ability to offer its hydrogen as humble tribute to wandering radical aggressors. The resulting vitamin E radical is stabilized by the electronic properties of the adjacent phenyl ring through delocalization as to be relatively unreactive. In plants, vitamin E is commonly found in chloroplasts where they protect against reactive oxygen species (ROS) produced as byproducts of photosynthesis. In humans, vitamin E plays a similar role. Vitamin E is known to incorporate into cell membranes where it is thought to protect against cellular damage caused by radicals present environmentally or resulting from metabolism by reacting with radicals before they are able to oxidize lipids and other cellular components. Regarding antioxidant ability, alpha-tocopherol has been shown to scavenge radicals faster than lipid substrates can be targeted [1]. 

The most biologically relevant form of vitamin E in humans is alpha-tocopherol, which is selectively ushered into use around the body by the alpha-tocopherol liver transfer protein, while gamma-tocopherol is suspected to hold importance as well though details are currently unknown [2]. A deficiency of vitamin E may result in neuromuscular and neurological problems, retinopathy or anemia, and excessive consumption of vitamin E may cause difficulty clotting [3]. Vitamin E is present in a number of vegetable oils, though processed vegetable oils contain lower tocopherol content due to damage during refining, leafy greens, nuts, seeds, sweet potatoes, avocadoes, eggs, liver and fortified breakfast cereals [4], many of which are typically present in a normal healthy diet. The recommended daily intake of vitamin E is 15 mg for adults, 11 mg for children ages 9-13 and 6-7 mg for children ages 1-8. Now you know stuff about this not well known vitamin, so go tell a friend and make sure they know too!

For more information on vitamin E, check out this description by the American oil chemists’ society (same as ref. 1). It’s a tad technical, but highly informative and an interesting read.