Vegetarians have a higher risk of suffering a stroke than meat eaters, researchers have found.
But those who avoid meat do have lower levels of coronary heart disease, the scientists also discovered.
The findings come as the popularity of vegetarian and vegan diets rise.
A study, tracking 48 188 people for 18 years, found vegetarians and vegans had a 20% higher risk of stroke than meat eaters.
This equates to three more cases per 1 000 people over 10 years – mainly due to haemorrhagic strokes, which occur when blood from an artery bleeds into the brain.
Vegetarians and vegans in the study were found to have lower blood cholesterol and lower levels of key vitamins – such as B12 – which could explain the link, researchers said. B12 stops inflammation in blood vessels. When inflammation builds up, a blood vessel can haemorrhage.
But vegetarians had a 22% lower risk of heart disease – which causes heart attacks and angina – than meat eaters. This is equivalent to 10 fewer cases per 1 000 people over a decade. Pescatarians – those who avoid meat but eat fish – had a 13% lower risk of heart disease.
This may be at least partly due to lower body weight, blood pressure and cases of diabetes among non-meat eaters, scientists said.
Just over half of the people in the study were meat eaters, a fifth ate only fish and a third were vegetarian or vegan. There were 2 820 cases of heart disease and 1 072 of stroke during the period of study, which tracked people from an average age of 45.
Lead researcher Dr Tammy Tong, from the Nuffield Department of Population Health at Oxford University, said more studies were needed "with a high proportion of non-meat eaters" to confirm the results and assess their relevance for public health.
Meat eaters in the study, which was published in the British Medical Journal, were found to be more likely to suffer from heart disease, with experts claiming that fans of sausages and steak were likely to be fatter, suffer from high blood pressure and cholesterol, and struggle with type 2 diabetes.
Dr Stephen Burgess, a cardiovascular expert at Cambridge University, said food studies were "notoriously difficult" because "it is hard to measure what people eat".
But he added: "This study suggests that taking up a vegetarian diet may not be universally beneficial for all health outcomes.
"When considering cardiovascular health, switching to a vegetarian diet should not be seen as an end in itself, but should be considered alongside additional dietary and lifestyle changes."
The research comes after a nutritionist last week warned that veganism may be putting the next generation’s IQ at risk as a lack of key nutrients in plant-based diets among pregnant women risks a baby’s brain development.
Tracy Parker, from the British Heart Foundation, said: "Whether you’re a committed carnivore, a veggie or a vegan, one way to reduce your risk of heart and circulatory diseases is to ensure you’re eating a balanced diet, packed with plenty of fruit and vegetables, wholegrains, beans, lentils, nuts and seeds."