Why do humans not synthesize Vitamin C, while most mammals do? To understand this apparently nonsensical evolutionary “paradox” we need to know this well-kept secret:
Humans require vitamin C from food because we are coming from a frugivorous ancestry – we do share many adaptive characteristics with frugivorous primates! This means the natural humans diet is a diet very high in fruit! The issue is, that our modern diets do not nearly include as much fruit (and therefore vitamin C) as our body is adapted to eat! To get an idea: chimpanzees, for example, have a diet that consists of around 70% fruits!
Don’t believe yet, that we are high-fruit beings? Check this out:
Humans have lost their functional vitamin C genes, while most other mammals produce their own vitamin C!
Why? Because it is only the frugivores (high fruit-eating species) that get enough vitamin C from their natural diet! Humans share the Vitamin C-loss-characteristic with other frugivores, like frugivorous bats, guinea pigs, and all primates. Now the seemingly malfunctioning mismatch starts to make sense – and seems even to be beneficial – when we know that we actually do not need vitamin C synthesis on our natural fruit diet!
What? Humans have lost their vitamin C genes?!
Yes, we have! Humans cannot synthesize vitamin C, while most mammals can! We have mutated “broken” genes in this regard. But why? What does the gene loss tell us about the natural human diet? It screams “we are frugivores!“
Omnivorous, carnivorous, and even herbivorous mammals – like dogs, cats, cows, rats, rabbits, elephants, most bats, and some birds – have functional vitamin C synthesis. Thus they have no need to obtain it from their diet.
Only frugivorous species lose their vitamin C production among different mammalian taxa – because their diet contains enough naturally.
In 2010 an article in Nature about the loss of vitamin C genes called “The Mystery of Vitamin C” could not find the answer as to why humans took this evolutionary turn: “We still do not know why humans lost the capability of synthesizing vitamin C. This event probably had evolutionary significance.” The author de Tullio calls the loss of such an important gene an “apparent paradox“, as it does not make sense in evolution to loose such a vital function.
The answer, however, becomes apparent when looking at the pattern among animals that have also lost their ability to synthesize Vitamin C: Only mammals with a high-fruit diet do not produce Vitamin C internally! This is yet another intriguing sign that humans are still adapted to a high-fruit diet!
Figure: A telling case of convergent evolution: Vitamin C gene loss has occurred independently in species with a high fruit diet (high vitamin C intake). This phylogenetic tree by Drouin et al. (2011) illustrates the ability of different mammals to produce vitamin C. Dark green species have functional genes, light green species do not. Screenshot from scientific american, showing that Lemurs (a primate with functional vitamin C genes) consume far less fruits than other primates”.
Thus, humans and other primates are not entirely alone with their dysfunctional vitamin C genes: This is a mutation that re-emerges in frugivores because frugivores take in large amounts of vitamin C from fruits. Across birds (many birds are frugivores), functional vitamin C genes were lost, and have even reappeared in birds that do not eat fruits.
Outsourcing the production of vitamin C helps the body save energy and invest it in other metabolic tasks. This is why loosing a gene can be an advantage in evolution. Nature saves energy, and the most energy-efficient genotype is successful, which is why unnecessary genes are lost.
Once again in so many other topics in health, nutrition and evolution, that things just start to make sense when frugivory (humans being specialized fruit-eaters) comes in the picture! See more biological features of humans that show we are frugivores here.
Optimal vitamin C intake can substitute many supplements
Because we cannot get enough Vitamin C in a modern diet (as we are adapted to a very high-fruit diet), most of us do not get an optimal amount of this key nutrient! The vital substance is involved in the metabolism of many other biochemical molecules. If we do not address the underlying shortcoming of Vitamin C, we are only treating the symptoms by taking in the lacking components!
Vitamin C is vital and essential for our organism and is required (here and here) in many important metabolic processes:
- as most abundant water-soluble antioxidant
- in collagen synthesis (skin and cartilage health)
- in the synthesis of carnitine
- in neurotransmitter synthesis
- in catabolic processes
- in the folic acid metabolism
- in the amino acid metabolism
- iron uptake
Those far-reaching functions indicate that obtaining optimal levels of vitamin C through diet – which is only possible on a high-fruit diet – would positively impact other nutrients and might substitute taking many nutritional supplements, rendering them unnecessary!
For example, carnitine and collagen are two popular supplements believed to be necessary, especially on a plant-based diet. However, the body produces them when vitamin C is present to do so. Folic acid is another nutrient that is believed to be in short supply, while sub-optimal vitamin C intake is a likely underlying cause!
Vitamin C genes defy the carnivore diet!
The “carnivore diet” has become popular lately. The diet often brings short-term health benefits because adopting this diet means leaving out all the toxic plant-protective anti-nutrients and irritants of a “standard diet”. Most diets are heavily based on grains, nightshade vegetables, and other plants with inflammatory components (read more here). In contrast, the human frugivore diet does not include such foods (learn more about biologically appropriate food groups for humans here).
However, on the long run, a carnivore diet is a really, really bad idea! Not only will it damage the kidneys and put ketogenic stress on the body, it is also severely deficient in nutrients from raw plant foods, including vitamin C. Gout and scurvy are historical examples of what happens on a high-meat diet!
But the pink elephant in the room here is that humans are not biological carnivores! We are biologically not adapted to a carnivorous diet! Humans are frugivores, which obligatorily need to take in Vitamin C from foods. Carnivores in nature, produce the molecule themselves and do not need it in their diet! Many frugivores can digest small amounts of animal-foods, however, not a full-meat or animal-food diet!
Further, claims that meat contains enough vitamin C are hard to hold up, in the light that biological carnivores and omnivores need to produce their vitamin C internally! Also, obtaining vitamin C from meat would require people to eat fresh raw meat, because vitamin C is destroyed by heating and cooking! An idea that instinctually makes us feel disgusted as a protective mechanism. However, eating their animal foods raw, is how Inuits survive in an environment without plant-based foods – but, their life expectancy on the traditional diet is low. True biological carnivores – like lions – produce vitamin C internally because raw meat seems not to be a suffice source.
To no surprise, lately, the carnivore community has started to adopt the idea of a “meat and fruit” diet to obtain the nutrition from raw foods and the nutrition we absolutely need for health as frugivorous beings! Fruits do not contain harmful Phyto compounds like grains, legumes, and even certain greens and veggies – the compounds that are being avoided by the “carnivore diet” followers.
Conclusion: Why Vitamin C is such a huge deal
Frugivores – including humans – do not synthesize vitamin C, because their species-specific diet contains high amounts naturally. Therefore, vitamin C is an essential micronutrient they need to obtain from the diet in large quantities! Humans, however, do not obtain nearly enough of it in most modern diets, which are “deficient” in fruit!
This is why vitamin C is such a huge deal in health – and why only a high-fruit diet can really address the root cause! Learn more about the human species-appropriate high-fruit diet here:
Go to How to do the Frugivore Diet
If you are new to this, visit this overview about frugivores and frugivory here!
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- G. Drouin, J.-R. Godin, B. Page, The genetics of vitamin C loss in vertebrates. Current Genomics. 12, 371–378 (2011), doi:10.2174/138920211796429736.(link)
- M.C De Tullio, The Mystery of Vitamin C. Nature news (available at https://www.nature.com/scitable/topicpage/the-mystery-of-vitamin-c-14167861/). (link)
- J. G. Goldman, Why lemurs have such strange diets. Scientific American (2018) (available at https://www.scientificamerican.com/article/why-lemurs-have-such-strange-diets/). (link)
- G. Drouin, J.-R. Godin, B. Page, The genetics of vitamin C loss in vertebrates. Current Genomics. 12, 371–378 (2011), doi:10.2174/138920211796429736. (link)
- S. Chambial, S. Dwivedi, K. K. Shukla, P. J. John, P. Sharma, Vitamin C in disease prevention and cure: An overview. Indian Journal of Clinical Biochemistry. 28, 314–328 (2013), doi:10.1007/s12291-013-0375-3. (link)
- L. McAuliffe, Do you need vitamin C on a carnivore diet? Dr. Robert Kiltz (2022) (available at https://www.doctorkiltz.com/vitamin-c-on-carnivore-diet/). (link)
- Life expectancy in the Inuit-inhabited areas of Canada, 1989 to 2003 – Findings. Health Reports: Life expectancy in the Inuit-inhabited areas of Canada, 1989 to 2003 (available at https://www150.statcan.gc.ca/n1/pub/82-003-x/2008001/article/10463/4149059-eng.htm). (link)