“I love the idea of getting all the vitamins and nutrients via greens but as I run the numbers on how much of each vitamin that is contained in the amount of greens in a typical recipe (i.e. one bunch of spinach), it makes me wonder if you can overdose on the fat soluble vitamins like A and K. I know with supplements in the past you had to be mindful but does your body handle vitamins derived from food sources differently?” — Andrew
This is an excellent question. I can see how it would be alarming to see vitamin levels that are extremely high in some green smoothie recipes.
For example, a simple green smoothie with one medium banana, one cup strawberries, and two cups of fresh baby spinach contains 191% RDA of vitamin A (as beta-carotene) and 245% RDA of vitamin K.
That sounds like a lot, but it’s nothing compared to the amounts you’d get if you used two cups of kale – 690% RDA vitamin A and 915% RDA vitamin K!
Is It Possible To Overdose On Vitamin A From Green Smoothies?
Pre-formed vitamin A, also known as retinol, is only found in animal-sourced foods (meat, eggs, dairy). Plants contain beta-carotene, which your body selectively converts to vitamin A (retinol) based on your body’s vitamin A status.
If your body requires vitamin A, it will convert beta-carotene. Otherwise, it will store beta-carotene in the liver and body fat without converting it to vitamin A.
Can You Overdose On Beta-Carotene
It is possible to “overdose” on beta-carotene, however. Carotenosis is a harmless condition where your body stores excess beta-carotene in the fat cells in your skin, giving it a yellow or orange hue.
Those with fair complexions are most susceptible to carotenosis than those with darker complexions. There are no other known health effects with carotenosis and the condition reverses itself when beta-carotene is consumed in smaller amounts.
It takes a LOT of beta-carotene to develop carotenosis, however. You’re not likely to get it from drinking a green smoothie or two every day. You almost have to get extreme with your overall diet and go out of your way to consume excessive amounts of foods rich in beta-carotene to turn your skin yellow.
Beta-Carotene, Vitamin A, and Retinol Activity Equivalents (RAE)
And another thing is that nutrition labels can be misleading about the amount of vitamin A contained in plant foods.
Food nutrition labels typically measure beta-carotene in International Units (IUs), but because beta-carotene isn’t the same thing as retinol vitamin A, IUs are not the most accurate indication of how much vitamin A activity you are getting from consuming beta-carotene rich foods like carrots.
Retinol equivalent (RE) and retinol activity equivalent (RAE) units have been devised to provide a better interpretation of how much actual vitamin A can be obtained from various foods, including those that contain retinol (meat, eggs, dairy) and those that contains carotenoids like beta-carotene (fruits and vegetables).
According to research published by the US Institute of Health in 2001, 1 RAE is equal to 1 microgram (mcg) of retinol (pre-formed vitamin A) or 12 micrograms of beta-carotene.
So the take home here is that nutrition labels for vitamin A, at least in regards to beta-carotene, aren’t exactly the most accurate indication of exactly how much vitamin A you are getting.
Your nutrient-tracking app might indicate that a medium carrot contains 340% RDA of vitamin A, but you are not actually consuming more than three times your recommended daily allowance of vitamin A since carrots contain no pre-formed vitamin A. They only provide the raw materials your body uses to make vitamin A, beta-carotene.
Also, your body does not convert excess beta-carotene into excess vitamin A, so there is no risk of overdosing on vitamin A from foods rich in beta-carotene.
What about Vitamin K?
There are two natural forms of vitamin K: K1 and K2.
Vitamin K1 (phylloquinone) is found in plants, particularly leafy greens. There are no known toxicity risk with consuming large amounts of vitamin K1 and no “tolerable upper limit” has been set for either vitamin K1 or vitamin K2 (menaquinone).
Basically, a green smoothie that contains almost 1000% RDA for vitamin K presents no toxicity risk in healthy people. However, there are toxicity risks with supplemental and synthetic forms of vitamin K.
I hope this clears up your concern about getting “excess vitamins” from green smoothies, as well as from fruits and vegetables.
My health mantra is always “whole foods are best”, and when it comes to getting the right amount of nutrients without overdoing it, fresh fruits, vegetables and green smoothies are the safest way to do it.