Drinking-water salinity, sodium exposure, and blood pressure among lactating mothers in coastal Bangladesh: a cross-sectional study

Rising sea levels linked to climate change are intensifying saltwater intrusion in coastal zones, which increases the risk of consuming saline drinking water and may have implications for maternal health. This research explored the relationship between drinking-water salinity, urinary sodium output, and blood pressure among breastfeeding mothers in coastal Bangladesh. A cross-sectional survey was carried out in Kalapara Upazila of Patuakhali District between July and December 2017. Using purposive sampling, 100 lactating mothers were enrolled. Information was gathered through structured interviews, body measurements, and blood pressure recordings. Spot urine samples were tested for sodium levels, and 24-hour sodium excretion was estimated using the Nerbass equation. Water samples from tube wells and ponds were analyzed for pH, electrical conductivity, sodium, and overall salinity. Statistical analyses, including correlation and multivariable linear regression, were applied to assess the links between water salinity, urinary sodium excretion, and systolic (SBP) as well as diastolic blood pressure (DBP). Overall, 58% of participants had estimated urinary sodium excretion above the WHO recommended level of 2 g/day (≈85 mmol/day). Mean salt concentration was significantly higher in tube-well water than in pond water (1420.67 ± 403.70 vs. 262.89 ± 794.50 mg/L; P<0.001). Water salinity was positively associated with urinary sodium excretion (P < 0.05). Estimated 24-h urinary sodium excretion was positively associated with SBP (β = 0.29, 95% CI: 0.17–0.36; P<0.001) and DBP (β = 0.23, 95% CI: 0.15–0.28; P<0.001). Associations remained significant after adjustment for age, education, water salinity, BMI, and MUAC (SBP: β = 0.36, 95% CI: 0.21–0.45; DBP: β = 0.21, 95% CI: 0.16–0.34; both P<0.001). Higher drinking-water salinity was associated with greater sodium exposure and higher blood pressure among lactating mothers. Improving access to low-salinity drinking water and strengthening community-based education on sodium exposure should be prioritized within maternal-health and climate-adaptation programmes in salinity-affected coastal communities.