High sodium intake from foods is linked to high blood pressure, but the health effects of sodium in drinking water has been less clear.

Now, a new study has found that healthy pregnant women in southwest coastal Bangladesh had their blood pressure rise if they drank water with high sodium content.

The study, published Monday in the American Heart Association’s Hypertension journal, noted that rising salinity also could affect crop productivity, and therefore, threaten the health and livelihood of coastal residents.

“We have a good piece of evidence of what is causing increased blood pressure in these women,” said Pauline Scheelbeek, Ph.D., a research fellow at Imperial College London’s School of Public Health at the time. “If we follow the Intergovernmental Panel on Climate Change’s latest predictions, these salinity problems linked with sea level rises and storm surges are expected to only further increase in the future.”

Scheelbeek, now a research fellow at the London School of Hygiene & Tropical Medicine, studied 701 healthy pregnant women living in Dacope, a poor rice-farming area of Bangladesh. She found that women who drank high-saline well and pond water had significantly higher average systolic blood pressure than rainwater-drinkers: an increase of 3.62 for pond water and a rise of 4.85 for well water.

The study found that women in Dacope drinking from tube wells drank on average 700 milligrams of sodium per liter. In such a hot climate, Scheelbeek said, someone might drink two to three high-saline liters a day, in addition to sodium consumed from food. U.S. dietary guidelines recommend less than 2,300 mg of sodium a day for people age 14 and older.

High blood pressure that develops during pregnancy increases the risk for preeclampsia, a leading cause of maternal death in developing countries, according to the World Health Organization.

A research assistant takes a pregnant woman's blood pressure in Dacope, Bangladesh.

A research assistant takes a pregnant woman’s blood pressure in Dacope, Bangladesh.

“The link between salinity in drinking water and hypertension is well established in literature,” said Susmita Dasgupta, Ph.D., lead environmental economist of the World Bank’s Development Research Group. She was not involved in the study.

Dasgupta’s research in coastal Bangladesh has related women’s ingestion of saltwater in the last month of pregnancy to infant mortality. She also found that high-salinity water decreased several quality of life factors, such as dietary nutrient sources and crop yields.

While poverty-stricken Bangladesh is considered “ground zero” of global warming, Scheelbeek notes that other low-lying delta areas in Southeast Asia, such as India and China, face similar salinity problems. So do parts of the United States, including Florida, and Australia, but people in those areas have more protection through embankments, for example, and better access to other sources of drinking water.

“For people who don’t have any other drinking water source to fall back on, it’s a big problem,” Scheelbeek said. “In many Southeast Asian countries, high levels of dietary sodium are the cause of a large proportion of the cardiovascular disease burden. Adding another source of sodium through drinking water would only add to these problems.”

High blood pressure can lead to heart disease and stroke, the two leading causes of death in the world. A 2014 study found that nearly 1.7 million deaths worldwide each year from cardiovascular causes are the result of too much sodium.

Scheelbeek thinks higher salinity is linked to climate change, but other man-made factors, such as shrimp farming and dam construction, let seawater move further inland. The Intergovernmental Panel on Climate Change’s 2007 report found that climatic change-induced weather events, such as cyclones and flooding, will likely lead to increased salinity of drinking water sources, and other research in Bangladesh suggests rising sea levels will mean larger areas of land will be affected in the future.

Rising sea levels could affect 1.4 billion people worldwide, according to the U.S. Geological Survey.

Scheelbeek said international guidelines are needed for maximum sodium content in drinking water. Such guidelines, she said, would encourage governments to monitor water quality and explore solutions.

The Leverhulme Trust funded the study.

Photos courtesy of Pauline Scheelbeek, Ph.D.