Epidemiological evidence on drinking water salinity and blood pressure: a scoping review

In addition to diet, drinking water can be an important contributor to the total body burden of salts. Water salinity (defined as the amount of dissolved salts in a body of water) has been associated with adverse health effects. We mapped the current research on drinking water salinity and its effects on blood pressure (BP). We aimed to identify knowledge gaps in the methodology and tools used in the epidemiological literature to address water salinity effects on BP. We performed a scoping review of epidemiological studies by searching PubMed and Web of Science databases from 1980 to 2022. Reviews, study comparisons, meta-analyses, commentaries, viewpoints, correspondence, protocols, studies in clinical settings, animal or in vitro studies, or not in English, were excluded. Epidemiologic studies including systolic/diastolic BP and/or the risk of hypertension as the main health outcome and drinking water salts (sodium, potassium, calcium, magnesium, including electrical conductivity and total dissolved solids) as the main exposures were included. After screening 246 articles, 29 articles were retained. Most studies were conducted in Bangladesh and USA (n = 9 and n = 9, respectively). The majority of studies were cross-sectional (n = 18; 62%). The study populations were adults (55%) or children (35%) or both (10%). Only eight (28%) studies did not collect urine samples and only three studies (10%) did not record participant BP. About half of the studies (n = 15, 52%) reported a positive significant (p < 0.05) association between salts in drinking water and higher BP and/or risk of hypertension; while 24% and 24% reported non-significant (p > 0.05) and significant (p < 0.05) negative associations (with lower BP mainly attributed to higher Mg, Ca, and K (rather than Na) levels in drinking water). More longitudinal studies are warranted to investigate the impact of drinking water salinization on cardiovascular health and risk of hypertension. Under a changing climate, this may be particularly important for coastal populations, as sea level rise in combination with the overexploitation of groundwater would differentially perturb the salinity of their drinking water supplies.