The Stroke Risk of Vegetarians

The first study in history on the incidence of stroke in vegetarians and vegans suggests they may be at higher risk.

“When ranked in order of importance, among the interventions available to prevent stroke, the three most important are probably diet, smoking cessation, and blood pressure control.” Most of us these days are doing pretty good about not smoking, but less than half of us exercise enough. And, according to the American Heart Association, only 1 in 1,000 Americans is eating a healthy diet and less than 1 in 10 is even eating a moderately healthy diet. Why does it matter? It matters because diet is an important part of stroke prevention.

The strongest evidence for stroke protection lies in increasing fruit and vegetable intake, with more uncertainty regarding “the role of whole grains, animal products, and dietary patterns,” such as vegetarian diets. One would expect meat-free diets would do great. Meta-analyses have found that vegetarian diets lower cholesterol and blood pressure, as well as enhance weight loss and blood sugar control, and vegan diets may work even better. All the key biomarkers are going in the right direction. Given this, you may be surprised to learn that there hadn’t been any studies on the incidence of stroke in vegetarians and vegans until now. And if you think that is surprising, wait until you hear the results.

“Risks of Ischaemic Heart Disease and Stroke in Meat Eaters, Fish Eaters, and Vegetarians - Over 18 Years of Follow-Up: Results from the Prospective EPIC-Oxford Study”: There was less heart disease among vegetarians. No surprise!  But there were  more stroke.

An understandable knee-jerk reaction might be: Wait a second, who did this study? Was there a conflict of interest?

What about overadjustment? When the numbers over ten years were crunched, the researchers found 15 strokes for every 1,000 meat eaters, compared to only 9 strokes for every 1,000 vegetarians and vegans. In that case, how can they say there were more strokes in the vegetarians? This was after adjusting for a variety of factors. The vegetarians were less likely to smoke, for example, so you’d want to cancel that out by adjusting for smoking to effectively compare the stroke risk of nonsmoking vegetarians to nonsmoking meat eaters. If you want to know how a vegetarian diet itself affects stroke rates, you want to cancel out these non-diet-related factors. Sometimes, though, you can overadjust.

The sugar industry does this all the time. This is how it works: Imagine you just got a grant from the soda industry to study the effect of soda on the childhood obesity epidemic. What could you possibly do after putting all the studies together to conclude that there was a “near zero” effect of sugary beverage consumption on body weight? Well, since you know that drinking liquid candy can lead to excess calories that can lead to obesity, if you control for calories effectively only comparing soda drinkers who take in the same number of calories as non-soda-drinkers, then you could undermine the soda-to-obesity effect, and that’s exactly what they did. That introduces “over adjustment bias.”

So getting back to the EPIC-Oxford study. Since vegetarian eating lowers blood pressure and a lowered blood pressure leads to less stroke, controlling for blood pressure would be an overadjustment, effectively only comparing vegetarians to meat eaters with the same low blood pressure. That’s not fair, since lower blood pressure is one of the benefits of vegetarian eating, not some unrelated factor like smoking. So, that would undermine the afforded protection. Did the researchers do that? No. They only adjusted for unrelated factors, like education, socioeconomic class, smoking, exercise, and alcohol.

The fact that vegetarians had greater stroke risk despite their lower blood pressure suggests there’s something about meat-free diets that so increases stroke risk it’s enough to cancel out the blood pressure benefits. But, even if that’s true, you would still want to eat that way. Stroke is our fifth leading cause of death, whereas heart disease is number one.
So, yes, in the study, there were more cases of stroke in vegetarians, but there were fewer cases of heart disease. If there is something increasing stroke risk, it would be nice to know what it is.

Homocysteine, Vitamin B12, and Stroke Risk?

nutritionfacts.org Sep 5, 2024

Vitamin B12 deficiency, common in individuals following plant-based diets without adequate supplementation or fortified foods, can lead to elevated levels of homocysteine in the blood, which is recognized as a risk factor for stroke. Interventional studies have demonstrated that vitamin B12 supplementation can improve arterial function in vegetarians with subnormal B12 status. This suggests that addressing B12 deficiency may mitigate the increased stroke risk associated with plant-based diets lacking sufficient B12 intake.Despite the evidence highlighting the importance of B12 supplementation, many vegetarians resist taking B12 supplements due to misconceptions about B12 deficiency being rare or assuming that dairy and eggs can provide an adequate B12 intake, emphasizing the need for education and awareness on the topic.