New study suggests that vegetarians may have a lower risk of heart disease but higher risk of stroke than meat eaters

Vegetarians may have a lower risk of heart disease but an increased risk of stroke, a new study has suggested.

The study, which was published recently in the BMJ, suggested that vegetarian (including vegan) and pescetarian diets may be linked to a lower risk of heart disease than diets that include meat, but vegetarians and vegans had a higher risk of stroke than meat eaters, particularly haemorrhagic stroke (caused by a bleed in the brain).

However, there is no need for vegetarians or vegans to be concerned about the stroke findings, as this is just one study and it is observational, meaning that the researchers cannot state that one thing (a vegetarian diet) directly causes another (an increased risk of stroke).

For this study, a team of researchers from the Nuffield Department of Population Health, Oxford University in the UK used data from the EPIC-Oxford study to explore the risks of heart disease and stroke in meat eaters, pescetarians (those who eat some fish but not meat) and vegetarians over an 18 year period.

The study, led by Dr Tammy Tong, included information on 48,188 people (average age 45 years) who were recruited between 1993-2001, and had no history of heart disease or stroke. They were then grouped into meat eaters (24,428), pescetarians (7,506), and vegetarians, including vegans (16,254).

The results found that there were 2,820 cases of heart disease and 1,072 cases of stroke during the study period, including 519 cases of ischaemic stroke (when a blood clot blocks the flow of blood and oxygen to the brain) and 300 cases of hemorrhagic stroke.

After taking account of potentially influential factors, such as medical history, smoking, use of dietary supplements and physical activity, pescetarians has a 13 per cent lower risk of heart disease than meat eaters and vegetarians had a 22 per cent lower risk.

This is equal to 10 fewer cases of heart disease in vegetarians than in meat eaters per 1,000 people consuming these diets over 10 years. The authors stated that the difference may be at least partly due to lower BMI and lower rates of high blood pressure, high blood cholesterol and diabetes linked to these diets.

In contrast, vegetarians and vegans had a 20 per cent higher risk of stroke than meat eaters, equivalent to three more cases of stroke per 1,000 people over 10 years, mainly due to a higher rate of hemorrhagic stroke.

Vegetarians and vegans in the study had lower circulating cholesterol and levels of several nutrients than meat eaters (e.g. vitamin B12), which could explain these findings, the authors suggested.

However, it is important to note that this is an observational study, and as such, can’t establish cause. And the findings may not be widely applicable because they were mainly based on white Europeans.

The study had a large sample size and long-term monitoring, but further research is needed to replicate the results in other populations and it should include further measurements of nutritional factors, said lead author Dr Tammy Tong.

“Additional studies in other large-scale cohorts with a high proportion of non-meat eaters are needed to confirm the generalisability of these results and assess their relevance for clinical practice and public health,” he said.

Commenting, Sarah Noone, Dietitian with the Irish Heart Foundation said, “This study adds to the growing body of evidence that increasing our intake of plant-based foods can help lower our risk of heart disease. However, it also found that vegetarians to be at a higher risk of stroke than meat eaters.”

“However, before those who follow a vegetarian diet become alarmed, it is important to note that as an observational study which followed what people ate over the years it only shows an association, rather than cause and effect e.g. it only shows a relationship but can’t show that one factor such as a vegetarian diet causes stroke.”

“Although the researchers did control for a number of confounding factors, they cannot control for everything so the association could have occurred for a number of reasons e.g. could it be due to potentially a lack of certain nutrients in vegetarian diets a couple of decades ago. Therefore, while interesting, this study needs to be viewed in the context of the entirety of the existent evidence base, which when it comes to nutritional science, is constantly evolving. In terms of the entirety of the evidence one-way people can reduce their risk of heart disease is to ensure they are eating a balanced diet, rich in fruit and vegetables, wholegrains, beans, lentils, nuts and seeds.”

For more information on ways to eat well for a healthy heart please see here

BMJ 2019;366:l4897