Drinking water salinity and raised blood pressure: evidence from a cohort study in coastal Bangladesh

Background – Millions of coastal inhabitants in South-east Asia have been experiencing increasing sodium concentrations in their drinking-water sources, likely to be partially due to climate change. High (dietary) sodium intake has convincingly been proven to increase risk of hypertension; it remains unknown, however, whether consumption of sodium in drinking water could have similar effects on health.

Objectives – We here present the results of a cohort-study in which we assessed the effects of drinking water sodium (DWS) on blood pressure (BP) in coastal populations in Bangladesh.

Methods – DWS, BP and information on personal, lifestyle and environmental factors were collected from 581 participants. We used generalised linear latent and mixed-methods to model effects of DWS on BP and assessed the associations between changes in DWS and BP when participants experienced changing water sodium levels and/or switched from “conventional” ponds or tube-wells to alternatives (Managed aquifer recharge [MAR] and rainwater harvesting) that aimed to reduce sodium levels.

Results – DWS-concentrations were highly associated with BP after adjustments for confounding factors. Furthermore, per 100mg/l lower sodium in drinking water, systolic/diastolic BP was lower on average by 0.95/0.57 mmHg and odds of hypertension lower by 14%. However, MAR did not consistently lower sodium levels.

Conclusions - DWS is an important source of daily sodium intake in salinity-affected areas, and a risk factor for hypertension. Considering the likely increasing trend in coastal salinity, prompt action is required. As MAR showed variable effects, alternative technologies for providing reliable, safe, low-sodium fresh-water should be developed alongside improvements in MAR and evaluated in ‘real-life’ salinity-affected settings.