Dietary glycine and blood pressure: the International Study on Macro/Micronutrients and Blood Pressure.

Available data have indicated independent direct relations of dietary animal protein and meat to the blood pressure (BP) of individuals. In this study, we aimed to assess whether BP is associated with the intake of dietary amino acids higher relatively in animal than in vegetable protein (alanine, arginine, aspartic acid, glycine, histidine, lysine, methionine, and threonine). The study was a cross-sectional epidemiologic study that involved 4680 persons aged 40-59 y from 17 random population samples in the People's Republic of China, Japan, the United Kingdom, and the United States. BP was measured 8 times at 4 visits; dietary data (83 nutrients and 18 amino acids) were from four 24-h dietary recalls and two 24-h urine collections. Dietary glycine and alanine (the percentage of total protein intake) were considered singly related directly to BP; with these 2 amino acids together in regression models (from model 1, which was controlled for age, sex, and sample, to model 5, which was controlled for 16 possible confounders), glycine, but not alanine, was significantly related to BP. Estimated average BP differences associated with a 2-SD higher glycine intake (0.71 g/24 h) were 2.0-3.0-mm Hg systolic BP (z = 2.97-4.32) stronger in Western than in East Asian participants. In Westerners, meat was the main dietary source of glycine but not in East Asians (Chinese: grains/flour and rice/noodles; Japanese: fish/shellfish and rice/noodles). Dietary glycine may have an independent adverse effect on BP, which possibly contributes to direct relations of animal protein and meat to BP.