Vegetarian Diet Linked to Lower Ischemic, Hemorrhagic Stroke Risk

Batya Swift Yasgur, MA, LSW

March 03, 2020

A vegetarian diet rich in nuts, vegetables, and soy has been linked to a lower risk of both ischemic and hemorrhagic stroke, new research suggests.

In two large cohorts of more than 13,000 individuals, investigators found a vegetarian diet was associated with a 60% to 74% decreased risk of ischemic stroke and 65% lower risk of hemorrhagic stroke.

"The take-home message is that lifestyle, especially healthful diets such as vegetarian diets, are important in the prevention and management of stroke," senior author Chin-Lon Lin, MD, chief executive officer, Buddhist Tzu Chi Medical Foundation, Hualien, Taiwan told Medscape Medical News.

The study was published online February 26 in Neurology.

Role of B-12

Vegetarian diets and other dietary patterns emphasizing plant foods have previously been linked to a lower risk of incident stroke, the investigators note.

On the other hand, many vegetarians have a low intake of vitamin B12, which might be responsible for raising homocysteine, an amino acid in the blood, thereby increasing the risk of stroke. In addition, some studies suggest animal protein may be beneficial for the prevention of hemorrhagic stroke.

"The combined effect of the supposed harm of high homocysteine and the supposed benefits of low blood pressure, glucose, and cholesterol (unique aspect of vegetarian diets) on stroke disease incidence is unclear," they add.

The researchers examined the incidence of overall, ischemic, and hemorrhagic stroke in vegetarians as well as nonvegetarians in two prospective cohorts in Taiwan and analyzed whether any association between vegetarian diet and stroke risk might be modified by vitamin B12 intake.

Participants in both cohorts were Tzu Chi Buddhists, about 30% of whom were full-time vegetarians (defined as avoidance of fish and meat).

Tables 1 and 2. Salient baseline differences between the cohorts  

Cohort 1 (n = 5050)

Characteristic

Nonvegetarians

Vegetarians

Participants

N = 3626

N = 1424

Mean age (years)

51.7

53.8

Male sex

47.2%

25.1%

Ever-smoking

21.2%

8.5%

Ever-alcohol consumption

18.0%

8.1%

Hypertension

14.5%

14.2%

Leisure physical activities

68.7%

64.7%

 

Cohort 2 (n = 8302)

Characteristic

Nonvegetarians

Vegetarians

Participants

N = 5583

N = 2719

Mean age (years)

49.2

50.1

Male sex

40.5%

27.9%

Ever-smoking

16.7%

10.2%

Ever-alcohol consumption

15.2%

11.0%

Hypertension

11.5%

9.4%

Leisure physical activities

84.7%

80.8%

 

Cohort 1 received a comprehensive health examination at baseline, provided demographic and lifestyle factors, and filled out a food frequency questionnaire (FFQ). Additionally, they underwent blood tests, including serum vitamin B12 level and fasting lipid profile.

Cohort 2 completed health status and lifestyle questionnaires as well as the FFQ, but anthropometric and biochemical data were not collected.

Vegetarians consumed more soy, vegetables nuts, dietary fiber, and plant protein and less dairy, animal protein, fat, and vitamin B12, compared with nonvegetarians.

Vegetarians in both cohorts had a higher proportion of inadequate intakes of vitamin B12, compared with nonvegetarians (64% vs 33%, respectively), and those in Cohort 1 had higher serum folate and homocysteine — a finding that remained even after adjusting for sex, smoking, and alcohol consumption.

Table 3. Stroke risks of vegetarians vs nonvegetarians in each cohort

Cohort

Overall Stroke Risk

Ischemic Stroke Risk

Hemorrhagic Stroke Risk

Cohort 1

(54 events)

1.16 [0.62 - 2.15] vs 1.99 [1.48 -2.67] per 1000 person-years

HR 0.28 [95% CI, 0.08 - 0.96]

Not analyzed because of too few events (n = 8)     

Cohort 2

(121 events)

0.95 [0.64 - 1.42] vs 1.88 [1.54 - 2.29] per 1000 person-years

HR 0.41 [0.19 - 0.88]

HR 0.34 [0.12 - 1.00]

 

In a subgroup of Cohort 1 (n = 1528) that underwent additional analyses of homocysteine, vitamin B12, and folate, an inverse association was found between vegetarian diet and lower overall stroke in those with inadequate vitamin B12 intake (ie, < 2.4 μg) but not in those with adequate vitamin B12 intake (P interaction = .046).

"Our explorative analysis showed that vitamin B12 intake may modify the association between vegetarian diet and overall stroke," the authors write.

The study contained several limitations, they note — in particular, since many participants with lower incidence of stroke also did not smoke or drink, the results may not be generalizable to other populations.

Contradictory Findings?

However, the results of the current study appear to differ somewhat from findings of the EPIC-Oxford study, published in September, that showed lower rates of ischemic heart disease and stroke in vegetarians compared with nonvegetarians, but higher rates of hemorrhagic stroke.

Addressing this discrepancy for Medscape Medical News, EPIC-Oxford study author Paul Appleby, MSc, senior statistician, Cancer Epidemiology Unit, University of Oxford, United Kingdom, who was not involved in the current study, said that the incidence of stroke in the Taiwan study (a total of 175 strokes) was smaller than in their study (1072 cases of stroke).

Moreover, Appleby continued, the Taiwan study used a "cruder level of adjustment" — ie, "smoking, alcohol drinking, and physical activity are adjusted for as a simple dichotomy in the Taiwan study."

He emphasized that this "does not negate the findings of the Taiwan study," which "makes a useful contribution to the field." But it is "important to put them into context," he said, noting that larger studies on diet and stroke risk "are more likely to produce reliable results."

Lin and colleagues acknowledge that their findings differ from those of the EPIC-Oxford study, but explained that the Buddhist vegetarians in their study differed in terms of their alcohol consumption and use of allium vegetables.

In addition, nearly 80% of vegetarians in the EPIC-Oxford study consumed varying degrees of alcohol and in a separate study, the EPIC-CVD case cohort study, researchers found a "clear trend" between alcohol consumption and stroke risk.

Moreover, Western vegetarians use "ample amounts" of garlic and other allium vegetables, in contrast to Asian vegetarians who avoid these vegetables.

Allium vegetables are "major sources of alliin/allicin," which are "known to inhibit platelet function and induce bleeding," the authors note.

Appleby alluded to a newly published study conducted by his group, which included more than 418,000 individuals. It shows "inverse associations of consumption of fruit and vegetables, dietary fiber, and dairy products, with risk of total and ischemic stroke; a modest positive association of red or processed meat consumption with risk of total and ischemic stroke; and a positive association of egg consumption with risk of total and hemorrhagic stroke."

Diet Matters

Also commenting on the study for Medscape Medical News, Teshamae Monteith, MD, associate professor of clinical neurology, University of Miami, Miller School of Medicine, Florida, said that the study "really confirms what we already know about plant-based diets, which is their association with advantageous cardiometabolic profile — especially hypertension, which is the number-one risk factor for stroke."

As plant-based diets become more popular, "this study also reminds us to hone in [on] the fact that we should remind patients to supplement and check for B12 deficiency," said Monteith, who was not involved with the study.

J. David Spence, MD, professor of neurology and clinical pharmacology, Western University, London, Ontario, told Medscape Medical News that, in his experience, "most doctors have no idea how important diet is, and this study highlights the importance of diet."

Spence, who is the coauthor of an accompanying editorial, described the North American diet as "terrible."

However, "people are starting to wake up, although it is a big struggle in my clinic to try to get people to go vegetarian even every other day," said Spence.

Also reached for comment, Thomas Sanders, DSc, emeritus professor of nutrition and dietetics, King’s College London, United Kingdom, said "most of the lifestyle factors favored the vegetarians, who had lower blood pressure, LDL cholesterol, a lower prevalence of type 2 diabetes, and also drank less alcohol."

Sanders, who was not involved with the study, noted that in East Asia, low LDL cholesterol "is associated with increased risk of hemorrhagic stroke, especially when blood pressure is raised; but in this cohort, the vegetarians came out ahead."

He cautioned that vegetarians "need to ensure they have adequate intakes of vitamin B12 and avoid consuming too much salt."

The establishment of the cohorts was supported by a grant from the Department of Health in Taiwan and a grant from Buddhist Dalin Tzu Chi General Hospital. The follow-up was supported by grants from the Buddhist Tzu Chi Medical Foundation and a grant from the Ministry of Science and Technology in Taiwan. Lin and study coauthors have disclosed no relevant financial relationships. Editorialist Spence and his coauthor have disclosed no relevant financial relationships. Appleby, Sanders, and Monteith have disclosed no relevant financial relationships.

Neurology. Published online February 26, 2020. Abstract, Editorial

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