Is salt intake an independent risk factor of stroke mortality? Demographic analysis by regions in Japan

We reported a remarkable regional difference within Japan in the incidence of end-stage renal disease. Regional differences were also well-known for salt intake, blood pressure (BP), and mortality from stroke, which remains one of the leading causes of death. Noting these regional differences, we examined mutual relationships among salt intake, BP, and stroke mortality in 12 regions of Japan. Data of salt intake, BP, and stroke mortality in 12 regions were collected from National Nutrition Survey (NNS-J), reanalysis of NNS-J, and Vital Statistics of National Population Dynamic Survey (Ministry of Health, Labor and Welfare), respectively. Significant regional differences were found in salt intake (P < .0001), mean arterial BP (P = .0001), and stroke mortality (P < .0001). Although annual changes in these parameters were also significant, their regional differences persisted. Salt intake had positive relationships with both mean arterial BP (r = 0.26, P = .0009) and stroke mortality (r = 0.26, P < .0001) across 12 regions, whereas mean arterial BP was not correlated with stroke mortality. Multiple regression analysis further identified salt intake as an independent factor to increase stroke mortality, but mean arterial BP was not a determinant. Compared with the four regions with lowest salt intake, odds ratios of stroke mortality adjusted by mean arterial BP were 1.04 (95% CI, 1.03–1.06) for the intermediate four regions and 1.25 (95% CI, 1.23–1.27) for the four regions with highest salt intake. These findings suggest that salt intake may have an adverse effect on stroke mortality independently of BP.