[Association of the combined estimated 24-h urinary Na/K ratio and body mass index with blood pressure: Cross-sectional data from the KOBE study].

Objective　Several studies have suggested that high dietary Na/K ratio and body mass index (BMI) increase the prevalence of hypertension. However, there have been a few reports on the combination of these two factors and their relationship with hypertension. This study aimed to examine the association of the combined estimated 24-h urinary Na/K ratio (24h-u-Na/K) (high or low) and BMI (high or low) with the risk of high blood pressure.Method　We performed a cross-sectional study involving 1,112 participants (340 men and 772 women) of the Kobe Orthopedic and Biomedical Epidemiological study (KOBE study) who had no cardiovascular diseases or current anti-hypertensive medications. Sex-specific analyses were performed. The 24h-u-Na/K ratio was calculated from an estimation formula using collected spot urine. Participants were divided into four groups based on their 24h-u-Na/K ratio (low or high) and BMI (low or high), with the cutoff points being the median and 25 kg/m2, respectively.　Participants with systolic blood pressure (SBP) ≥130 mmHg or diastolic blood pressure (DBP) ≥80 mmHg were diagnosed with high blood pressure. Odds ratios (ORs) for high blood pressure according to the combined risks of high 24h-u-Na/K and BMI were examined with a logistic regression analysis.Results　The average SBP/DBP for men and women was 122.7/77.9 and 113.3/69.1 mmHg, respectively, and prevalence of high blood pressure among men and women was 47.4% and 21.3%, respectively. The mean BMI was 22.8 kg/m2 for men and 20.9 kg/m2 for women. The median 24h-u-Na/K was 3.2 for men and 3.1 for women. The prevalence of high blood pressure (men, women) was the highest in the group in which both 24h-u-Na/K and BMI were high (60.0%, 62.9%; men: P=0.273; women: P<0.001). In the same group, the multivariate-adjusted ORs for high blood pressure were significantly higher for both men (2.59; 95% confidence interval [CI]: 1.15-5.86) and women (10.78; 95% CI: 4.87-23.88) compared to the reference group with both factors classified as low. Women with low BMI but high 24h-u-Na/K also demonstrated a higher risk for high blood pressure (OR: 1.62; 95% CI: 1.10-2.40).Conclusion　The risk of high blood pressure was the highest when both BMI and 24h-u-Na/K were high. The current specific healthcare guidance in Japan is focused on obese individuals. However, in order to prevent hypertension more effectively, additional focus should be placed on the Na/K diet. Increased intake of vegetables and fruits and reduced intake of salt should be strongly recommended.

Estimated 24 h Urinary Sodium-to-Potassium Ratio Is Related to Renal Function Decline: A 6-Year Cohort Study of Japanese Urban Residents.

The effect of the sodium-to-potassium ratio (Na/K) on renal function within the clinically normal range of renal function are limited. We investigated the effects of an estimated 24 h urinary Na/K (e24hUNa/K) on a 6-year renal function decline among 927 urban Japanese community dwellers with no history of cardiovascular diseases and medication for hypertension, diabetes, or dyslipidemia. We partitioned the subjects into quartiles according to the e24hUNa/K. The estimated glomerular filtration rate (eGFR) was calculated using the chronic kidney disease epidemiology collaboration (CKD/EPI) formula and renal function decline was defined as an absolute value at or above the third quartile of the eGFR decline rate. A multivariable logistic regression model was used for estimation. Compared with the first quartile of the e24hUNa/K, multivariable-adjusted odds ratios (ORs) for eGFR decline in the second, third, and fourth quartiles were 0.96 (95% confidence interval: 0.61-1.51), 1.06 (0.67-1.66), and 1.65 (1.06-2.57), respectively. These results were similar when the simple spot urine Na/K ratio was used in place of the e24hUNa/K. Apparently healthy urban residents with an almost within normal range mean baseline eGFR and high e24hUNa/K ratios had an increased risk for a future decline in renal function. Reducing the Na/K ratio may be important in the prevention of chronic kidney disease in its early stage.