Could the apparent increased risk of stroke in vegetarians be due to an inverse causal relationship? And what about vegetarians compared to vegans?
In the EPIC-Oxford study “Risks of ischemic heart disease and stroke in meat, fish and vegetarian consumers during 18 years of follow-up”, it is not surprising that vegetarian diets were associated with less heart disease (10 fewer cases per 1,000 people per decade compared with meat eaters), but vegetarian diets were associated with three further cases of stroke. So eating vegetarian appears to reduce the risk of cardiovascular disease by 7% overall, but why the extra risk of stroke? Could it simply be reverse causality?
When the studies have shown For example, if we consider that those who quit smoking have a higher mortality rate than those who continue to smoke, we suspect that there is “reverse causality.” When we see a link between quitting smoking and dying, rather than quitting smoking leading to people dying, it is more likely that being “affected by some life-threatening disease” led people to quit smoking. It is the same reason that abstainers can They seem to have more cirrhosis of the liver; their failing liver led them to stop drinking. This is the “sick-guy-quitter effect,” and it can also be seen when people stop eating meat.
As you can see below and at 1:16 of my video. Vegetarians and stroke risk factors: Vitamin D?
new vegetarians can It seems that vegetarians have more heart disease than non-vegetarians. Why might an older person suddenly start eating vegetarian? Well, they may have just been diagnosed with heart disease, so that may be why there seem to be higher rates of new vegetarians – an example of the disease-withdrawal effect. To control for that, you can throw out the first five years of data to make sure the diet has a chance to start working. And indeed, when you do that, the true effect is clear: a significant reduction in heart disease risk.
So does that also explain the apparent increased risk of stroke? No, because researchers have yet to… found The risk of stroke is higher even after the first five years of data have been omitted. What’s going on? Let’s dig into the data to find clues.
What happens when you break down the results by stroke type and type of vegetarian (vegetarian versus vegan)? As you can see below and at minute 2:09 of my videothere are There are two main types of stroke: ischemic and hemorrhagic. The most common are ischemic strokes, which cause clots, in which an artery in the brain is blocked, as opposed to hemorrhagic or bleeding strokes, in which a blood vessel in the brain ruptures. In the United States, for example, is around 90:10, with nine out of ten strokes of the clotting (ischemic) type and one out of ten bleeding (hemorrhagic), the latter be The type of stroke that vegetarians seem to have significantly more of. Now, statistically, vegans don’t have a significantly higher risk of any type of stroke, but that’s terrible news for vegans. Do vegans have the same risk of stroke as meat-eaters? What is it that raises their risk of stroke so much that it’s negating all their natural advantages? The same could be said for vegetarians, too.
Although this was the first study on the incidence of stroke in vegetarians, have There have been about half a dozen studies on stroke mortality. The various meta-analyses have consistently found a significantly lower risk of heart disease for vegetarians, but the lower stroke mortality was not statistically significant. Now, there is a new study that may give Vegetarians take some solace in the fact that at least they are not at increased risk of dying from a stroke, but that is terrible news for them. Statistically, vegetarians have the same stroke mortality rate as meat eaters. Again, what is going on? What is raising their risk of stroke so high that it is negating all their natural advantages?
Let’s look at a couple of possibilities. As you can see in the chart below and at minute 3:48 of my videoIf we look at the vitamin D levels of vegetarians and vegans, tend have consistently lower vitamin D levels than meat eaters. associated at higher risk for stroke. But who has higher levels of the sunshine vitamin? Those who run outdoors and exercise, so maybe that’s why their risk for stroke is higher. What we need are randomized studies.
When you look In people who have been randomly assigned at birth to have lower vitamin D levels throughout their lives, there is no clear indicator of increased stroke risk, so the link between vitamin D and stroke is probably not cause and effect.
We’ll explore some other possibilities below.
So far in this series, we have looked at What to eat and What not to eat for the prevention of stroke, and if Vegetarians have a higher risk of stroke.
It’s worth reiterating that vegetarians aren’t at increased risk of dying from a stroke, but they do seem to be at increased risk of having one. How is that possible? Meat is a risk factor for stroke, so how could not eating it cause more strokes? There must be something about a plant-based diet that increases stroke risk so much that it counteracts the benefit of not eating meat. Could it be because plant-based eaters don’t eat fish? Next, we’ll focus on omega-3s. For other videos in this series, check out the related posts below.
However, vitamin D certainly has benefits. Here This is a video sample where I explore the evidence.
