Dr. Michael J. Orlich of Loma Linda University in California and colleagues examined all-cause and cause-specific death in a group of 73,308 male and female Seventh-Day Adventists.
Researchers assessed dietary patients using a questionnaire that categorized study participants into five groups: non-vegetarian; semi-vegetarian; pesco-vegetarian, which includes seafood; lacto-ovo-vegetarian, which includes dairy and egg products, and vegan, which excludes all animal products.
However, the study noted vegetarian groups tended to be older, more highly educated and more likely to be married, to drink less alcohol, to smoke less, to exercise more and to be thinner.
"Some evidence suggests vegetarian dietary patterns may be associated with reduced mortality, but the relationship is not well established," the study noted.
There were 2,570 deaths among study participants during an average follow-up time of nearly six years -- six deaths per 1,000 person years.
The study, published in Internal Medicine, found the adjusted hazard ratio for all-cause mortality in all vegetarians combined versus non-vegetarians was 0.88, or 12 percent lower.
The association also appears to be better for men with significant reduction in cardiovascular disease mortality and ischemic heart disease death in vegetarians versus non-vegetarians. In women, there were no significant reductions in these categories of mortality, the study said.