Why Do Vegans Have a Higher Risk of Stroke?

The claim that vegans face a higher stroke risk comes mainly from one large British study that found elevated rates of hemorrhagic stroke among people who avoid meat, though the finding for vegans specifically did not reach statistical significance due to small numbers. The reality is more layered than the headline implies. Several plausible biological pathways could explain a genuine increase in certain stroke types, but the epidemiological evidence is inconsistent across populations, and much of the risk appears tied to specific nutrient shortfalls that are preventable with targeted supplementation.

What the Largest Studies Actually Show

The study that launched most of the concern followed roughly 48,000 people in the United Kingdom for about 18 years. Compared with meat eaters, vegetarians and vegans combined had a 20% higher rate of total stroke and a 43% higher rate of hemorrhagic stroke, the type caused by bleeding in the brain. At the same time, they had a 22% lower rate of ischemic heart disease. When vegans were analyzed as a separate group, their point estimate for total stroke was 35% higher than meat eaters, but the confidence interval was wide enough to include no difference at all, meaning the result could easily be due to chance given how few vegan stroke cases there were.¹

A later meta-analysis pooling 13 cohort studies with over 840,000 participants found that vegetarians had a modest, non-significant trend toward higher total stroke risk compared to nonvegetarians. The combined relative risk was 0.90 for stroke overall, actually slightly favorable, though the confidence intervals crossed the line of no effect in both directions. For vegans specifically, there was not enough pooled stroke data to draw a separate conclusion.² A separate systematic review focusing specifically on vegan diets found that none of the included studies reported a statistically significant increase or decrease in any cardiovascular outcome for vegans. One study within that review did suggest vegans might face a higher ischemic stroke risk, but again, the result was not statistically significant.³

The picture gets even murkier when you look outside Europe. Two large Taiwanese cohorts found vegetarians had substantially lower stroke risk across the board, including both ischemic and hemorrhagic subtypes. In one cohort, vegetarians had about 74% lower ischemic stroke risk and roughly 65% lower hemorrhagic stroke risk compared to nonvegetarians.⁴ That is nearly the opposite of the British result. These conflicting findings suggest that the stroke risk linked to plant-based diets is not a universal biological inevitability but depends heavily on what people are actually eating, what nutrients they supplement, and background population factors like genetics, baseline blood pressure, and cooking traditions.

The Hemorrhagic Stroke Question and Very Low Cholesterol

The specific stroke subtype that showed up most clearly in the EPIC-Oxford data was hemorrhagic stroke, not the more common ischemic kind. That distinction matters because the two types have different risk profiles. Ischemic strokes are caused by clots blocking blood flow to the brain. Hemorrhagic strokes are caused by bleeding, typically from a weakened blood vessel that ruptures. Low cholesterol, which is common on plant-based diets, is a well-known risk factor for heart attacks and ischemic stroke. But its relationship with hemorrhagic stroke runs in the opposite direction.

A systematic review and meta-analysis including over 1.4 million participants found that higher total cholesterol was associated with about a 31% lower risk of hemorrhagic stroke. Higher LDL cholesterol was also linked to lower hemorrhagic stroke risk.⁵ The proposed explanation is that cholesterol plays a structural role in cell membranes, including the cells lining blood vessels. When cholesterol drops very low, vessel walls may become more fragile and prone to rupture under the mechanical stress of high blood pressure.⁶

Vegans tend to have meaningfully lower total and LDL cholesterol than omnivores. When omnivores switched to a vegan diet for just four weeks in one observational study, their cholesterol intake dropped roughly tenfold.⁷ Over years, that sustained reduction in dietary cholesterol and saturated fat can push blood lipid levels well below the population average. For most cardiovascular outcomes this is protective, but it may tip the balance toward hemorrhagic stroke risk in people who also have uncontrolled high blood pressure or other vessel-weakening factors. The effect is not unique to veganism; it has also been observed in people taking high-dose statin drugs that drive LDL to very low levels.

Vitamin B12 Deficiency and Damaged Arteries

If there is one nutrient deficiency that repeatedly surfaces in discussions of vegan cardiovascular risk, it is vitamin B12. Plants do not produce B12, and without supplementation or fortified foods, vegans inevitably become deficient. The downstream effects are not trivial. B12 deficiency causes a buildup of homocysteine in the blood, an amino acid that at elevated levels damages blood vessel linings and promotes the kind of arterial stiffness and plaque formation that sets the stage for stroke. A review of the evidence found that the vast majority of studies reported average homocysteine levels above the risk threshold of 10 micromoles per liter in vegetarians, and that each additional 5-micromole rise above that threshold was associated with a roughly 20% increase in the risk of circulatory problems, including stroke.⁸

The good news is that this pathway responds well to supplementation. A trial in vegetarians with low B12 status found that B12 supplements significantly lowered homocysteine and improved two important measures of arterial health: the ability of blood vessels to dilate on demand, and the thickness of the carotid artery wall, a marker of early atherosclerosis. After 24 weeks of open-label B12 supplementation, carotid artery wall thickness improved from an average of 0.69 mm to 0.65 mm.⁹ That suggests the artery damage linked to B12 deficiency is at least partially reversible, not a permanent consequence of going plant-based.

Omega-3 Gaps and Platelet Behavior

Another nutrient gap that distinguishes vegans from omnivores and even from fish eaters is long-chain omega-3 fatty acids, specifically EPA and DHA. The plant-based omega-3, ALA, which is found in flaxseed, walnuts, and chia seeds, must be converted in the body to EPA and DHA. Humans do this conversion very inefficiently, with estimates ranging from about 5% to 10% for EPA and less than 1% for DHA in some studies. This means vegans who rely solely on ALA-rich plant foods can end up with substantially lower circulating levels of the long-chain omega-3s that help regulate blood clotting and inflammation in the brain.

The effects on clotting are genuinely unclear. Some early studies found that vegetarian diets were associated with increased platelet aggregation, meaning platelets clumped more easily, which was attributed to the lack of long-chain omega-3s that normally keep platelets from getting too sticky.¹⁰ But a more recent systematic review looking at six cross-sectional studies and four intervention trials found inconsistent results. Two of the six observational studies did report increased platelet function in vegetarians, while three found no difference at all, and the intervention trials similarly showed no consistent effect.¹¹ This is an area where the evidence is genuinely thin and contradictory, and it would be premature to declare that vegans face a clear platelet-related stroke risk.

That said, the theoretical concern is coherent even if the clinical evidence has not caught up. EPA and DHA contribute to producing anti-inflammatory signaling molecules in the body. Without adequate levels, the balance of pro- and anti-inflammatory processes in blood vessels could shift in ways that affect both clot formation and vessel integrity. Algae-derived DHA supplements, which are entirely plant-based, provide a direct way for vegans to bypass the poor ALA conversion rate.

Iodine, Thyroid Function, and an Overlooked Pathway

One nutrient gap that gets far less attention than B12 in vegan health discussions is iodine. Dairy products and seafood are the primary dietary sources of iodine in many Western countries, and vegans avoid both. A Norwegian study found that vegans had a median urinary iodine concentration of 43 micrograms per liter, which falls in the range of moderate iodine deficiency. Vegetarians and pescatarians were also below optimal levels. About half of all three groups had total daily iodine intakes below the estimated average requirement.¹²

Iodine deficiency leads to impaired thyroid function, and hypothyroidism has its own set of cardiovascular consequences including elevated cholesterol (paradoxically, in the opposite direction from the typical vegan profile), increased blood pressure, and arterial stiffness. Subclinical hypothyroidism, the early stage where thyroid hormone levels are just slightly off, is associated with modest increases in cardiovascular event risk. The Veganuary study mentioned earlier found that even a short four-week switch to a vegan diet significantly reduced iodine intake in former omnivores, and supplementation only partially corrected the deficit, with average intake still falling below the recommended level.⁷ Seaweed and iodized salt are available plant-based solutions, but iodine content in seaweed varies wildly by species, and many vegans who prioritize whole or unprocessed foods may not use iodized salt regularly.

Why Results Differ So Much Between Populations

One of the most striking things about the vegan-stroke literature is the flat contradiction between British and Taiwanese data. In the UK, avoiding meat was associated with more hemorrhagic stroke. In Taiwan, it was associated with dramatically less hemorrhagic stroke.⁴ Several explanations have been proposed, and none of them are fully satisfying on their own.

Diet composition differs enormously between a British vegan and a Taiwanese Buddhist vegetarian. Taiwanese vegetarian diets tend to include soy products as a dietary staple, providing more complete protein and isoflavones that may support vascular health. The background prevalence of B12 supplementation, iodine fortification policies, and availability of fortified foods all vary between regions. Taiwanese vegetarians in these cohorts also tended to avoid alcohol and smoking at higher rates than British vegetarians, which may confound the comparison. And genetic factors matter too. Variants in the FADS1 and FADS2 genes, which encode the enzymes responsible for converting short-chain omega-3s into the long-chain forms, vary in frequency across populations. Impaired activity of these enzymes due to genetic variation can disrupt the body’s ability to produce EPA and DHA from plant sources, and the prevalence of these variants differs between European and East Asian populations.¹³

There is also a measurement problem that haunts all nutritional epidemiology. Self-reported dietary data are notoriously unreliable, carrying both random errors and systematic biases that are difficult to correct for. Researchers have acknowledged that intake biomarkers could produce more reliable results, but such biomarkers exist for only a handful of nutrients and are expensive to apply in large cohorts. This means every large dietary study, whether it shows higher or lower stroke risk in vegans, is built on an imperfect foundation of self-reported food records.

Practical Steps That Likely Reduce the Risk

The mechanisms that most plausibly link vegan diets to hemorrhagic stroke risk are all nutritional deficiencies that can be addressed. The evidence does not suggest that avoiding animal products is inherently dangerous for brain blood vessels. It suggests that a vegan diet without attention to a handful of critical nutrients leaves gaps that may, over years or decades, shift the balance of certain risk factors.

The highest-priority supplements for vegans concerned about cardiovascular and cerebrovascular health are B12 and algae-based DHA. B12 supplementation demonstrably lowers homocysteine and improves arterial function in vegetarians with subnormal levels.⁹ Iodine deserves more attention than it typically gets; vegans in countries without mandatory iodine fortification should consider iodized salt or a supplement, since dietary sources are limited and seaweed content is unpredictable.¹² Blood pressure monitoring is also relevant, since the hemorrhagic stroke concern specifically involves vessel rupture under pressure. Vegans already tend to have lower blood pressure on average, which is protective, but those who do have hypertension are the ones most vulnerable to the vessel-fragility effects of very low cholesterol.

The Role of TMAO and a Possible Vegan Advantage

One biochemical pathway that actually works in vegans’ favor is worth noting. Trimethylamine N-oxide (TMAO) is a compound produced when gut bacteria metabolize carnitine and choline, nutrients concentrated in red meat, eggs, and some dairy. The liver converts the bacterial byproduct into TMAO, and high blood levels of TMAO have been strongly correlated with cardiovascular disease and acute cardiac and vascular events. Vegans generally produce less TMAO because their gut microbiome adapts to a plant-based substrate. Even when vegans are experimentally fed carnitine, their gut bacteria produce less of the precursor compound than the gut bacteria of habitual meat eaters.

This lower TMAO production is one plausible reason why plant-based diets are consistently associated with lower rates of ischemic heart disease. The EPIC-Oxford study found that vegetarians had about a 22% lower rate of ischemic heart disease, and fish eaters about a 13% lower rate, compared to meat eaters.¹ That benefit for ischemic heart disease was much more robust statistically than the stroke risk was in the other direction. When evaluating the overall cardiovascular tradeoff of a vegan diet, the ischemic heart disease advantage is large, consistent across studies, and applies to a much more common condition than hemorrhagic stroke.

How Reliable Is the “Higher Risk” Claim

It is worth being honest about the quality of evidence behind the headline claim. The meta-analysis pooling multiple cohorts found no statistically significant increase in total stroke risk for vegetarians, and there was not enough data to conduct a separate vegan-only analysis for stroke.² The systematic review specific to vegan diets found no significantly increased or decreased risk of any cardiovascular outcome.³ The single study that generated the alarming headlines, EPIC-Oxford, is excellent in its size and follow-up length, but it is one cohort in one country, and the vegan-specific analysis within it was underpowered. Most of the elevated signal came from the broader vegetarian group, which includes people eating dairy and eggs as well as people with very different dietary patterns from strict vegans.

The biological plausibility is there. Low cholesterol weakening blood vessels, B12 deficiency damaging arteries through homocysteine, and omega-3 shortfalls affecting inflammation and platelet function all make mechanistic sense. But the epidemiological confirmation remains patchy. Researchers who have studied this closely tend to frame the risk not as an inherent danger of plant-based eating, but as a consequence of nutritional gaps that happen to be more common among vegans who do not supplement carefully. The distinction matters, because the solution is not to add meat back to the diet. It is to add a few milligrams of B12, some algal DHA, and a reliable source of iodine.

1
The BMJ. 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
2
PubMed Central. Vegetarian and vegan diets and the risk of cardiovascular disease, ischemic heart disease and stroke: a systematic review and meta-analysis of prospective cohort studies
3
The Journal of Nutrition. A Systematic Review of the Association Between Vegan Diets and Risk of Cardiovascular Disease
4
PubMed Central. Vegetarian diet and incidence of total, ischemic, and hemorrhagic stroke in 2 cohorts in Taiwan
5
PubMed Central. The Association between Low Levels of Low Density Lipoprotein Cholesterol and Intracerebral Hemorrhage: Cause for Concern?
6
PubMed Central. Low LDL-Cholesterol and Hemorrhagic Risk: Mechanistic Insights and Clinical Perspectives
7
PubMed Central. Adoption of a Short-Term (4-Week) Vegan Diet as Part of ‘Veganuary’ Significantly Reduces Saturated Fatty Acid (SFA), Cholesterol, B12, and Iodine Intake in Omnivorous Individuals—An Observational Study
8
PubMed. Is vitamin B12 deficiency a risk factor for cardiovascular disease in vegetarians?
9
The Journal of nutrition, health and aging. Vitamin B-12 supplementation improves arterial function in vegetarians with subnormal vitamin B-12 status
10
The American Journal of Clinical Nutrition. The effect of vegetarian diet, plant foods, and phytochemicals on hemostasis and thrombosis
11
Polish Archives of Internal Medicine. The effect of plant-based diets on thrombotic risk factors
12
PubMed Central. Vegans, Vegetarians and Pescatarians Are at Risk of Iodine Deficiency in Norway
13
PubMed Central. FADS1 and FADS2 Gene Polymorphisms Affect Omega-3 and Omega-6 Erythrocyte Fatty Acid Composition and Influence the Association Between Dietary Fatty Acid Intake and Lipid Profile in Brazilian Adults