Estimated protein intake and blood pressure in a screened cohort in Okinawa, Japan

We examined the relation between protein intake and blood pressure in a screened cohort in Okinawa, Japan. A total of 1,299 screened subjects, 885 men and 414 women, were examined at the Okinawa General Health Maintenance Association. Daily intake of sodium (Na) and potassium (K) was estimated from Na, K, and creatinine excretion by the method of Kawasaki et al., and daily protein intake was estimated by the method of Maroni et al. as the estimated daily urinary excretion of urea nitrogen. Mean (SD) daily protein intake was 71.8 (18.6) g in men and 54.0 (13.5) g in women, and the mean (SD) daily protein intake per unit kg body weight was 1.1 (0.2) g/kg in men and 1.0 (0.2) g/kg in women. In men, both systolic blood pressure (SBP) and diastolic blood pressure (DBP) were higher in those with lower protein intake (LP; < 1.0 g/kg/day) than in those with higher protein intake (HP; greater than or equal to 1.0 g/kg/day) (p<0.05 for DBP). In women, both SBP and DBP were higher in those with LIP than in those with HP, but these differences were not statistically significant. However, urinary excretion of both Na and K was lower in those with LP than in those with HP, respectively, both in men and women (p<0.0001). In summary, estimated daily protein intake was about 1.1 g/kg in men and 1.0 g/kg in women. Despite the higher urinary excretion of Na, both SBP and DBP tended to be lower in those with higher daily protein intake, particularly in men.