Vitamins

Weekly Focus: Vitamins

What I learned this week

March 24, 2024

Leah Jamison

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This week is a deep dive into one of my favorite topics – vitamins! Here are the highlights of what I learned this week about these micronutrients, with examples of their roles in some cool metabolic pathways.

1. Vitamin A and Eye Health

I think we’ve all heard about how vitamin A is “good” for our eyes. But do you know why? I certainly didn’t. Don’t worry, I’ve got a simple breakdown plus a tangible takeaway for when you’re wandering the supplements isle.*

 Retinol, retinal, retinoic acid, retanoids … you need a sharp retina just to notice the difference! These words are slightly different because they refer to slightly different chemical structures of the same root chemical compound: retinol. Let’s start there.

Retinol comes from the diet (primarily from dairy products) and your body will readily convert it into retinal. Retinol and retinal molecules can actually convert back and forth between each other, just based on whichever is needed. Retinal molecules can also come from … beta carotene?! Yep, beta carotene is considered “provitamin” A since it gets converted into retinal by your body’s fantastic enzymes. Beta carotene is in all the orange produce, so that’s where the infamous carrot comes in – as an aside, you’ll actually find it more concentrated in sweet potatoes than in carrots. So, you’ll start with either retinol or beta carotene from your diet, but once inside your body, both will be converted into retinal.

Carrots are often the food we think of when it comes to Vitamin A, but there are several other great sources to consider trying!

• Sweet potato
• Butternut squash
• Pumpkin
• Apricot
• Cantaloupe
• Spinach
• Kale
• Bok choy

Keep in mind that plant-based sources of vitamin A contain it the form of beta-carotene. Beta carotene falls under another group of molecules called carotenoids, which is a fancy word for the orange, purple, red, and yellow pigments found in plants, bacteria, and fungi.

Retinal sits at a metabolic crossroads – it has options. It’s also special because it’s the version of vitamin A your eyes use to perceive light. Retinal can either be shuttled off to the retina for this very purpose, or it can be converted into retinoic acid. This conversion step is a one way street. Once retinoic acid forms, it can’t go back to being retinal. Your body uses retinoic acid to help “read” your DNA and produce more proteins, so it’s pretty important! But it’s not the molecule that your eyes use. This brings me to my supplement isle takeaway: don’t go looking for retinoic acid on the ingredients label if you’re purchasing something to improve eye health. Retinoic acid isn’t the form used by the eye, and unlike provitamin forms like retinol and beta-carotene, retinoic acid cannot be interconverted into retinal. I’m not saying retinoic acid is bad in any sense, I’m just saying it’s not doing much for you in the direction of eye health.

Your retinas require vitamin A in the form of retinal in order to see. This is a neat little cycle where cis-retinal molecules will attach to the protein opsin and wait for light to strike. Once light enters the retina and hits this retinal-opsin pair, the retinal molecule takes a “hit” and becomes trans-retinal. This conversion triggers a signaling pathway to the brain (details are outside my scope of knowledge here), and the retinal-opsin pair breaks apart. The trans-retinal gets converted back into cis-retinal and the cycle restarts. Recycling at its finest. Cis-retinal can come from recycling or from the blood if you’ve recently consumed a bunch of sweet potatoes or duck liver.

*disclaimer: I am not a registered dietitian (yet!) and none of my inferences and suggestions should be taken as prescriptive in any way nor are they intended to serve as medical advice. Please consult a dietitian or medical professional before making any changes to diet, supplementation use, medication use, and exercise.

2. Vitamin D and Mushrooms

I have spent most of my adult life thinking that sunshine was the one and only way to get vitamin D. Nope!

According to a 2018 review published in Nutrients, mushrooms exposed to UV light (sunshine or artificial) are a decent source of vitamin D.

I’ll still look forward to a daily dose of sunshine, but this mushroom plot twist was exciting to learn about.

Read the full study here: Cardwell 2018

3. Vitamin C, E, and Glutathione

Turns out vitamins C and E double as antioxidants! Antioxidants are a large umbrella group, and until this year I was unaware that a vitamin could be both … vitamin and antioxidant! Not all vitamins, though. Only A, C, and E make the cut. Let’s talk a bit more about C and E.

Like partners in crime, vitamins C and E are going to work together to neutralize dangerous free radicals. Free radicals are another umbrella term, one category sitting underneath this umbrella is called “Reactive Oxygen Species” or ROS for short. ROSs are oxygen-based molecules that are missing electrons and therefore are electrically charged. They’ll wreak havoc on any part of your body that could offer them this missing electron – think DNA, cell membranes, and other proteins. Our body is constantly working to scavenge these guys and “neutralize” them – ie, give them that electron that they want.

Vitamin E is a front line player in the antioxidant VS free radical battle. Vitamin E finds ROSs and sacrifices itself, essentially. It gives them an electron. The biochemical version of donating an arm to the enemy. Now Vitamin E is the one that needs an electron, and this is where it gets interesting.

Sunflower seeds have the most Vitamin E per gram than any other nut or seed out there. Almonds are a close second!

Vitamin E’s trusty electron donor is – you guessed it – vitamin C. Vitamin C donates its own electron to Vitamin E. Great, but now we’ve got another problem. Where does Vitamin C restore its (now missing) electron? Glutathione.

Glutathione is a hot topic in current scientific literature because it’s been shown to have all these great antioxidant roles and activities outside of the single pathway I’m describing here. See this article for more details on glutathione. So glutathione donates an electron to vitamin C, and the final electron donor in this weirdly long pathway of middle men is called NADPH. In short, NADPH is ubiquitously found in all tissues and comes from a breakdown of glucose. So you’ll need a diet with vitamins E and C in order to wrangle your ROSs.

Here is the full sequence of electron donors:

NADPH -> Glutathione -> Vitamin C -> Vitamin E -> ROS

So there you have it! These were my favorite little nuggets of nutrition science from this week’s lessons. I hope you enjoyed reading and learned something, too! Let me know your thoughts and questions in the comments below, I love to nerd out with you guys 🙂