Most adults have either high blood pressure (hypertension) or prehypertensive blood pressure levels, according to background information in the article. Previous studies have found evidence that meat eaters generally have higher blood pressure than vegetarians. Other research looked directly at the effect of high overall protein intake and found that people with higher total protein intake are likely to have lower blood pressure, the authors report.
Paul Elliott, M.B., Ph.D., from Imperial College London, and colleagues analyzed data from the INTERMAP study, which included 4,680 people (2,359 men and 2,321 women) aged 40 to 59 years from four countries. They measured each participant's systolic and diastolic blood pressure eight times at four visits in a three- to six-week period. Each person wrote down everything they had eaten and drank during the previous 24 hours, including dietary supplements, at each visit. Urine samples were also taken on the first and third examinations.
Judging by their food records and urine samples, those who ate more vegetable protein were more likely to have lower blood pressure than those who ate less vegetable protein. Though the researchers noted a slight association between animal protein and high blood pressure, this link disappeared when they accounted for participants' height and weight. There was no link between total protein intake and blood pressure, in contrast to previous studies.
The researchers are unsure exactly how vegetable proteins might affect blood pressure, but note from their data that amino acids may play a role. Some of these building blocks of protein have been shown to influence blood pressure, and different amino acids were present in diets high in vegetable protein than in those that contained more animal protein. Other dietary components of vegetables, such as magnesium, also may interact with amino acids to lower blood pressure.
"Our results are consistent with current recommendations that a diet high in vegetable products be part of a healthy lifestyle for prevention of high blood pressure and related chronic diseases," the authors write. "Definitive ascertainment of a causal relationship between vegetable protein intake and blood pressure awaits further data from randomized controlled trials, especially regarding the effect of constituent amino acids on blood pressure."
(Arch Intern Med. 2006; 166:79-87. Available pre-embargo to media at www.jamamedia.org.)
Editor's Note: This study was supported by a grant from the National Heart, Lung, and Blood Institute, Bethesda, Md.; by the Chicago Health Research Foundation; by a grant from the Ministry of Education, Science, Sports, and Culture, Tokyo; and by national agencies in the People's Republic of China and in the United Kingdom.