Close adherence to the Japanese diet is not associated with a high prevalence of hypertension: the Japan Epidemiology Collaboration on Occupational Health Study

While the traditional Japanese diet has been suggested to increase blood pressure due to its high Na content, whether the contemporary Japanese diet is associated with blood pressure remains elusive. We developed a traditional Japanese diet score (nine items: white rice, miso soup, soy products, vegetables, mushrooms, seaweeds, fish, salty food and green tea) and a modified version by substituting white rice with whole-grain rice, reverse scoring for salty food and adding fruits, raw vegetables and dairy products using data from 12 213 employees from Japanese companies. Hypertension was defined as a blood pressure of 140/90 mmHg or more or the use of antihypertensive drugs. A multi-level Poisson regression model with a robust variance estimator was used to calculate prevalence ratios (PR) and 95 % CI while adjusting for covariates. The adjusted PR (95 % CI) of hypertension for the lowest through highest quartiles of the traditional Japanese diet score were 1·00 (reference), 0·94 (0·88, 1·02), 0·98 (0·90, 1·06) and 0·96 (0·90, 1·02), respectively (<i>P</i> for trend = 0·29), while those for the modified Japanese diet score were 1·00 (reference), 0·96 (0·94, 0·99), 0·95 (0·85, 1·05) and 0·94 (0·87, 1·01), respectively (<i>P</i> for trend = 0·10). In this cross-sectional study, close adherence to the traditional Japanese diet was not associated with the prevalence of hypertension, whereas there was a suggestion of an inverse association between the modified Japanese diet and the prevalence of hypertension.