Heart disease is the largest cause of death in developed countries.
The study looked at 44,561 men and women living in England and Scotland who were enrolled during the 1990s in a separate Oxford study looking at links between cancer and nutrition.
Researchers used this database because of the unusually high number of vegetarians enlisted: 34% of the people.
All the people were asked about their health and lifestyles when they joined. This included questions about diet and exercise, as well as other factors affecting health such as smoking and drinking alcohol. Almost 20,000 participants also had their blood pressures recorded and gave blood samples for cholesterol testing.
The volunteers were tracked until 2009. During that time, researchers recorded 1,066 people with heart disease and 169 deaths from heart disease.
The researchers found that vegetarians had a 32% lower risk of developing heart disease than those who ate fish and meat. They did not differentiate between red and white meat, nor did they track how much meat was eaten.
Blood Pressure and Cholesterol
"We didn't look at the specific components of the vegetarian diet that might contribute to the lower risk of heart disease in this study, but because the vegetarians have lower blood cholesterol, it is probably because they have a lower intake of saturated fat and a higher intake of polyunsaturated fat,” says Francesca Crowe, who led the study.
Crowe says the vegetarians also ate more fruits, vegetables, and fiber, which might have contributed to their lower risk of heart disease.
The researchers say lower blood pressure among the vegetarians is likely to be an important factor.
Additionally, vegetarians typically had a lower body mass index (BMI) and fewer cases of diabetes (although these were not found to significantly affect the results). If the results are adjusted to exclude the effects of BMI, vegetarians are 28% less likely to develop heart disease, the researchers say.
The study appears in the American Journal of Clinical Nutrition.