Do Humans Need Vitamin C?

Do Humans Need Vitamin C?

Do Humans Need Vitamin C?

Do humans need Vitamin C?” I wondered…

When I first decided to experiment with the Carnivore Diet, I had some concerns.

I was going from Keto to Carnivore and worried about the lack of fiber and the elimination of many “healthy” plant-based antioxidants. I was curious about its associations with cancer and correlations with disease. I wondered about what a carnivore’s carbon footprint must look like.

But what concerned me the most was vitamin C.

Vitamin C

Vitamin C is a powerful antioxidant and Linus Pauling, one of my favorite scientists in history, believed it was the solution to all diseases of civilization. Together with vitamin E it reduces lipid peroxidation. It’s a cofactor in many enzymatic reactions – including those in the making of collagen and carnitine.

But what I was most concerned about was that inadequate vitamin C can result in scurvy.


Vitamin C is essential in the synthesis of collagen. Many animals can synthesize vitamin C out of glucose. But humans as well as primates like monkeys and apes lost this ability about 60 million years ago. We lack the enzyme (L-gulonolactone oxidase – GULO) that is required in the last step in the synthesis of Vitamin C from glucose.

Because of this, we must consume our vitamin C or risk the consequences of scurvy – fatigue, weakness, gum disease, poor wound healing, and potentially death from infection or bleeding.


Looking through the lens of evolution has influenced my nutrition views as much as looking through the lens of microscopes. Evolution doesn’t tend to just drop things because they are no longer useful. It selects for advantages.

But what’s the advantage of not synthesizing an essential vitamin?

Uric Acid

In our evolutionary history, we also loss the ability to break down uric acid. And there is a striking parallel between the loss of the ability to synthesize vitamin C and the loss of the ability to break down uric acid.

Uric acid is a major antioxidant, more potent than Vitamin C.

Losing the ability to break down uric acid resulted in higher levels of uric acid in primates. These high levels are thought to explain the relatively long lifespans of apes.

It’s entirely possible, if not likely, that increased uric acid took over many of the antioxidant functions of vitamin C.

Glucose-Ascorbate Antagonism Theory (GAA Theory)

When we look at animals that make their own vitamin C, we find they make less of it when carbohydrates are low.

Which is interesting – low carbohydrates would indicate a lower vitamin C intake from the diet and presumably a higher need to make it endogenously.

Yet we see the opposite.

The more carbohydrates/glucose an animal eats, the more vitamin C it gets from its food, AND the more it makes endogenously.

This suggests that more vitamin C is needed in a glucose-based metabolism.

It also suggests that Vitamin C requirements may be less in low-carbohydrate conditions.

This makes sense though.

Glucose and vitamin C look very similar. There molecules are nearly identical. They even use the same pathways for absorption into cells. Because of this they directly compete with each other for uptake into cells. And glucose wins out preferentially.

Orange Juice

orange juice and vitamin cThis is why drinking orange juice doesn’t make sense (at least for vitamin C purposes). It may have a lot of vitamin C, but it’s high sugar content blocks that vitamin C from getting used.

This is also why diabetics with high blood sugar have strikingly similar symptoms that are seen with scurvy. They are vitamin C deficient even though they may be getting “adequate” intake from their diet or supplements. The glucose blocks out the vitamin C.

In fact, the benefit of vitamin C in disease may not have anything to do with its antioxidant properties. Rather, high dose vitamin C could sometimes compensate for the glucose overload and insulin resistance that is characteristic of many of the diseases of modern man.

Linus Pauling was on to something after-all.

Meat, Vitamin C, and Scurvy

Our food labeling would lead us to believe that meat doesn’t contain vitamin C. But it does.

And in the absence of carbohydrates far less vitamin c is needed. It doesn’t have to constantly compete with glucose for uptake.

The amount of vitamin C to prevent scurvy is just 10 mg/day in the context of a high carb diet.

In a low/no carb diet, even less is needed.

On the Carnivore Diet, the meat content plus the absence of carbs creates an environment that doesn’t result in scurvy.

Vitamin C’s role as a cofactor in hydroxylation reactions (transferring a hydroxl group to the amino acids lysine and proline), is what helps make the building blocks of collagen. But meat comes “pre-packaged” with hydroxylysine and hydroxyproline – further bypassing much of the requirement for vitamin C.

So even though the amount of dietary vitamin C consumed on a meat-based diet may be lower compared to that of a plant-based diets with fruits and vegetables, the former has a lower need for vitamin C with higher bioavailability.

Antioxidant Properties

Well if we don’t need Vitamin C to prevent scurvy on a meat-based diet, surely we need its antioxidant properties, right?

Well, no.

Endogenously synthesized uric acid and glutathione (natural human antioxidants) are much more powerful and take over much of the roles that vitamin C would play. Plus, in a low carb diet these powerhouses are up-regulated.

In essence, we “turn on” more of our most powerful antioxidants. In addition glutathione and uric acid spare vitamin C by recycling it.

So Do Humans Need Vitamin C?

Yep we do.

But how much is entirely dependent on the context of one’s diet. If you eat a high carb diet, you need a lot more vitamin C to compete with those carbs for uptake.

Contrary to popular belief, meat does contain vitamin C, and in the context of a low/no carb diet like the Carnivore Diet, very little vitamin C is actually needed to prevent scurvy. This environment also up-regulates our naturally produced antioxidants. It’s likely the loss of endogenously synthesized vitamin C was not detrimental to our hominid ancestors but rather conferred a competitive advantage (perhaps from the uptick of the likes of uric acid and glutathione).

However, a mismatch, the “discordance theory,” between our current diet and ancestral physiology is likely the cause of vitamin C deficiencies and their association with disease.

As is seen time-and-again in research, the clinical manifestation (vitamin C deficiency for example) is the consequence, not the cause, that can only be understood in the proper context.

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