"Vegetarians and Stroke Risk Factors —Vitamin B12 & Homocysteine?"
Leonardo da Vinci had a stroke.
Might his vegetarian diet been to blame?
“His stroke… may have been related to an increase in homocysteine level
because of the long duration of his vegetarian diet.”
A suboptimal intake of vitamin B12, which is common in those
eating plant-based diets unless they take B12 supplements
or eat B12-fortified foods regulartly, can lead to an increased level
of homocysteine in the blood, which is accepted as an important
risk factor for stroke. “Accepted” may be overstating it;
there’s still controversy surrounding the connection between
homocysteine and stroke risk. But, those with higher homocysteine levels
do seem to have more atherosclerosis in the carotid arteries
that lead up to the brain compared to those with single digit
homocysteine levels, and do seem to be at higher risk for
clotting strokes in observational studies, and more recently
bleeding strokes, as well as increased risk of dying from
cardiovascular disease, as well as all causes put together.
Even more convincing is the genetic data.
About 10% of the population has a gene that increases
homocysteine levels about 2 points, and they do appear to have
significantly higher odds of having a stroke.
Most convincing would be randomized double-blind placebo-controlled trials
to prove homocysteine lowering with B vitamins can lower strokes,
and that indeed appears to be the case for clotting strokes,
those with homocysteine-lowering interventions more than
5 times as likely to reduce stroke compared to placebo.
Ironically, one of the arguments against the role of homocysteine
in strokes is that assuming that vegetarians have lower vitamin B12 levels
then the incidence of stroke should be increased among vegetarians,
but supposedly this wasn’t the case, but it had never been tested,
never been studied…. until, now,
and vegetarians do appear to be at higher risk
and no wonder, as about a quarter of the vegetarians
and nearly three-quarters of the vegans studied were B12 depleted
or deficient, resulting in extraordinarily high homocysteine levels.
Why so much B12 deficiency? Because only a small minority
were taking a dedicated B12 supplement.
And unlike the U.S., B12 fortification of organic foods isn’t allowed;
so, while U.S. soymilk and other products may be fortified with B12,
UK products may not. We don’t see the same problem among U.S. vegans
in the Adventist study, presumed to be because of the B12 fortification
of commonly eaten foods.
It may be no coincidence that the only study I was able to find
that showed a significantly lower stroke mortality risk
among vegetarians was an Adventist study.
But start eating strictly plant based without B12 fortified foods
or supplements, and B12 deficiency can develop, but that was only for
those not eating sufficient foods fortified with B12.
Those eating plant-based not being careful about getting
a regular reliable source of B12 have lower B12 levels
and consequently higher homocysteine levels.
The only way to prove vitamin B12 deﬁciency is a risk factor
for cardiovascular disease in vegetarians is...
to put it to the test.
When researchers measured the amount of atherosclerosis
in the carotid arteries, the main arteries supplying the brain,
between vegetarians and nonvegetarians, no significant difference was found.
They both look just as bad even though vegetarians tend to have
better risk factors such as cholesterol and blood pressure.
They suggest B12 deficiency is playing a role, but how do they know?
Some measures of artery function weren’t any better either.
Again, they surmise vitamin B12 deﬁciency overwhelming
the natural plant-based benefits. Yes, the beneﬁcial effects
of vegetarian diets on cholesterol and blood sugars need to be advocated,
but the necessity to correct vitamin B12 deﬁciency
in vegetarian diets cannot be overstated.
Sometimes vegetarians did even worse. Worse artery wall thickness.
Worse artery wall function, raising concern, more than a decade
before the new stroke study, about the vascular health of vegetarians.
Yes, their B12 was low, yes, their homocysteine was high
suggesting that vitamin B12 deﬁciency in vegetarians might have
adverse effects on their vascular health, but what you’d need is
an interventional study, where you give them B12 and see if
that fixes it and… Here we go, a double-blind, placebo-controlled,
randomized crossover study and the title gives it away:
Vitamin B-12 supplementation improves arterial function
in vegetarians with subnormal vitamin B-12 status.
So, that may explain it.
Compromised vitamin B12 status among those eating more plant-based diets
due to not taking B12 supplements, or regularly eating
vitamin B12 fortified foods may explain the higher stroke risk
found among vegetarians.
Unfortunately, many vegetarians resist taking vitamin B12 supplements
due to misconceptions, like holding on to the old myth that
deﬁciency of this vitamin is rare among plant-based eaters.
A common mistake is to think that the presence of dairy products
and eggs in the diet, as in a lacto-ovo vegetarian diet can still
ensure a proper intake of B12, despite excluding meat.
Now that we may have nailed the cause, maybe future studies should
focus on identifying ways of convincing vegetarians to routinely
take vitamin B12 supplements in order to prevent a deﬁciency.