Study links salty drinking water to higher blood pressure, especially in coastal areas

(Press-News.org) Salt is usually something people are warned to limit in food, not drinking water. But a global analysis suggests sodium in tap water may be an overlooked contributor to high blood pressure, particularly in coastal regions. 

The study, published in BMJ Global Health, found that higher salinity in drinking water was associated with higher blood pressure and an increased risk of hypertension. 

The research was led by Florida International University scientists, including Rajiv Chowdhury, chair of the Department of Global Health at FIU’s Robert Stempel College of Public Health & Social Work, with collaborators from Johns Hopkins University, Vanderbilt University, and the Pan American Health Organization. 

Researchers analyzed data from 27 population-based studies involving more than 74,000 participants in the United States, Bangladesh, Vietnam, Kenya, Australia, Israel, and several European countries. 

Blood pressure is commonly measured using an inflatable cuff placed around the upper arm. As the cuff tightens and gradually releases, a monitor records the force of blood pushing against artery walls. Results are expressed as systolic pressure over diastolic pressure, such as 120/80 millimeters of mercury (mm Hg). 

People exposed to higher salinity in drinking water had higher average blood pressure than those exposed to lower salinity. Systolic blood pressure – the top number in a reading – was about 3.2 mm Hg higher, while diastolic blood pressure – the bottom number – was nearly 2.8 mm Hg higher. 

Higher drinking water salinity also was associated with a 26% increased risk of hypertension, with the strongest and most consistent associations observed in coastal populations. 

“These are modest increases at the individual level,” Chowdhury said, “but when large populations are exposed, even small shifts in blood pressure can have significant public health effects. To put it in perspective, the risk level observed in this study for water salinity is like other established cardiovascular risk factors, such as low physical activity, which increases hypertension risk by approximately 15 to 25%.” 

Salt can enter drinking water through several pathways, including saltwater intrusion into groundwater, which supplies nearly half of the world’s drinking water. The issue is most common in coastal regions, where freshwater and saltwater systems sit close together underground. 

More than 3 billion people worldwide live in coastal or near-coastal areas, many of which rely on groundwater for drinking water, the authors note. While dietary sodium has long been recognized as a risk factor for high blood pressure, sodium from drinking water is not currently considered in most hypertension prevention guidelines. 

“Food remains the primary source of sodium for most people,” Chowdhury said. “But where salinity is elevated, drinking sources may add to total intake. Checking local water quality reports if available and focusing on overall dietary sodium are practical steps, particularly for individuals who need to manage blood pressure.” 

The researchers say the findings highlight the importance of considering environmental exposures alongside individual behaviors when addressing high blood pressure risk. 

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