Background: An inverse association between total protein intake and blood pressure has been reported in Western countries. Such evidence is limited in the Japanese population, however, whose major protein sources are plants and seafood.
Methods: We conducted a population-based cross-sectional study of 986 men and 1,636 women, aged 40-74 years, in a Japanese rural community to examine the association between blood pressure levels and urea nitrogen concentrations in spot urine.
Results: The concentration of urea nitrogen in spot urine, an indicator of total protein intake that was validated by 24-h urea nitrogen excretion and 24-h dietary research, was inversely associated with systolic blood pressure levels for men: a 238 mg/dl increase in urea nitrogen concentration was associated with a 2.1 mm Hg lower mean systolic blood pressure. For women, a weaker and nonsignificant inverse association was observed. There was no association between urea nitrogen concentrations and diastolic blood pressure levels in either sex. Total protein intake estimated from spot urine was also inversely associated with systolic blood pressure levels for men: a 19.2 g/day increase in estimated protein intake was associated with a 1.5 mm Hg lower mean systolic blood pressure.
Conclusion: A urinary biomarker for total protein intake was inversely associated with systolic blood pressure levels for men in a Japanese general population.