Can A Vegan Diet Lead to Brain Shrinkage?


brain image

Back in 2008, an Oxford professor published a study that concluded that low vitamin B12 levels in the elderly correlated to brain shrinkage.

It was a well-done study, published in one of the most respected peer-reviewed journals. Here’s a PDF of the study if you’d like to read it.

But ever since then, many who dislikes vegans have started saying that a vegan diet leads to brain shrinkage because vegan diets have no B12 in them.

Note that the study doesn’t mention the word “vegan” a single time.

So let’s clear things up once and for all, because there’s a lot of confusion thanks to these people.

Vegan Brain Shrinkage Research

The research team found 107 elderly volunteers (between 61 and 87 years old) who had a healthy brain (no impairment initially).

They were tested each year with a variety of cognitive tests and an MRI scan. Their blood was also collected to test levels of certain vitamins (B12) and markers.

By the end of the 5 year study, they found that patients with the greatest loss of brain volume had lower levels of vitamin B12 in their blood plasma.

That makes sense, since B12 is known to be important for a healthy brain.

So what does that have to do with veganism?

Veganism and Vitamin B12

There’s no vitamin B12 in plants themselves, but there is B12 in animal products. That’s why vegans and certain types of vegetarians can develop a B12 deficiency if they’re not careful. 

What most people don’t know is that all vitamin B12 comes from certain types of bacteria.

This bacteria is found in soil by the roots of plants.

Our produce is washed well before we eat it, so we get very little of this bacteria, and virtually no B12 from plants.

However, animals often consume dirt while they eat, ingesting some B12, plus the B12 producing bacteria. They can then store that bacteria in their guts, and it will produce B12 that they can absorb (humans can produce it like this, but it’s too late in the gut to absorb it).

This is why there’s B12 in animal products, but it all comes from the same bacteria that come from the soil beneath plants.

Avoiding Brain Shrinkage as a Vegan

Vitamin B12 is vital for brain function, as the study above shows, so it is mandatory for vegans to get it through a supplement (or start eating plants straight from the garden).

But as long as you’re supplementing, there’s no risk of running low on B12. We use a very small amount of it each day, and full stores can last years before running out.

A vegan diet could lead to brain shrinkage if you didn’t supplement vitamin B12. However, all vegans that supplement B12 have no additional risk of brain shrinkage.

Finally, I’ve compiled a list of the best vegan vitamin B12 supplements if you need help choosing one.

About the author

Dale Cudmore

Your friendly neighborhood vegan from Toronto. Chemical engineer turned semi-professional soccer player and freelance nutrition writer. I've been vegan for years and try to make life easier for others by sharing what I've learned.


  • Actually B12 is produced by specific bacteria in the rumin of herbivorous ruminant animals and not by bacteria in the soil. What needs to be in the soil for this to iccur is cobalt which will be taken up by the plants (like grass) which the herbivores eat and is fermented into B12 by thier bacteria. B12 in spil occurs from the animals feces and is not otherwise naturally occurring.

    • You have a few things incorrect here, but are mostly correct.

      First, “Vitamin B12 is synthesized only by certain bacteria and archaeon”, which is why you can also get B12 from algae.

      Second, bacteria precedes all animal life, although it can be transported by animals (and their feces) among other mechanism. Ultimately bacteria is what produces all vitamin B12, certain animals just need cobalt as a precursor to this process.

      Finally, there is a symbiotic relationship between those ruminants and the bacteria producing B12, but the same can be said for plants:

      Vitamin B12 is produced by soil microbes that live in symbiotic relationships with plant roots. During the 1980s, an undergraduate research course taught by Walker resulted in a novel method for identifying mutant strains of a soil microbe that could not form a symbiotic relationship with a plant.