Drinking water salinity and blood pressure in coastal Bangladesh: follow-up of a population-based cohort in a climate-vulnerable region

Objectives: To investigate the association between drinking-water sodium concentration and blood pressure among non-pregnant women living in a high-salinity, climate-vulnerable coastal region of Bangladesh.

Design: Follow-up study of women originally enrolled in a population-based study conducted during pregnancy between 2009 and 2011.

Setting: Rural coastal subdistrict in southwest Bangladesh affected by saltwater intrusion and seasonal drinking-water insecurity.

Participants: Of 1208 women enrolled in the original study, 900 were located in 2018 and 740 non-pregnant women were re-enrolled and included in the present analysis. Eligible participants were women from the original study who were alive and still residing in the study area; women who had migrated could not be located, declined participation or were pregnant at follow-up were excluded.

Primary and secondary outcome measures: The primary outcome was blood pressure, measured using a standardised protocol. Main exposure was sodium concentration in household drinking water and reported drinking-water source. Secondary analyses assessed temporal changes in drinking-water sodium between 2009 and 2018 and associations with water source, perceived taste and changes in exposure over time.

Results: Mean sodium concentration in household drinking water was highest in groundwater/tubewell users (933 mg/L, SD 372). Approximately 22% of women consumed drinking water contributing up to 94% of the WHO-recommended maximum daily sodium intake, assuming 2 L/day consumption. Sodium concentrations increased in seven of nine administrative unions between 2009 and 2018 (p=0.013). Compared with women consuming water containing <200 mg/L sodium, exposure to >1000 mg/L was associated with higher odds of raised diastolic blood pressure (adjusted OR 2.30, 95% CI 1.40 to 3.77; p=0.001). Restricted cubic spline and piecewise regression models suggested a non-linear association, with a threshold near 1000 mg/L. No statistically significant association was observed for systolic blood pressure.

Conclusions: High sodium concentrations in drinking water were associated with elevated diastolic blood pressure among women in coastal Bangladesh. Drinking-water salinity may represent an under-recognised cardiovascular risk in climate-vulnerable coastal populations. These findings support the need for salinity surveillance, climate-resilient low-sodium drinking-water supplies and further research to inform health-based standards for sodium in drinking water.