Dr Pauline Scheelbeek, Department of Epidemiology and Biostatistics, explores the link between salty drinking water and high blood pressure.
It’s a well-established fact that high salt consumption (over 5 grams a day) can lead to increased blood pressure. In western countries such as the UK, most of the salt we consume comes from (mostly processed) foods that you may eat on a daily basis, such as bread, cheese or bacon. High blood pressure can lead to several chronic diseases, including coronary artery disease, a condition that can cause a heart attack. If you suffer from high blood pressure a doctor will therefore often advise you to lower your salt intake.
Consuming too much salt is not only a problem in the West: in coastal areas of Southeast Asia, drinking water sources, rather than food, are responsible for high salt intake by the population. These low-lying areas experience frequent floods, which contaminate ponds and small wells which local people rely on for their drinking water. As climate change affects weather patterns, these floods are predicted to become more frequent in the future.
How does drinking salty water affect health?
Previous work at Imperial College London has shown that the health of pregnant women in southern Bangladesh was possibly affected by drinking water with high levels of salt. The researchers found that women drinking highly salty water were 5 times more likely to suffer from pre-eclampsia – a condition during pregnancy characterised by high blood pressure – than women drinking water with low salt concentrations [1, 2].
Given these results, it seemed likely that drinking salty water might also affect blood pressure in the general (non-pregnant) population. However, since high blood pressure often goes without symptoms and routine blood pressure measurements in non-pregnant adults are rarely performed in these areas, the scale of the problem remained unknown.
To find out more, my research team initiated a study that measured how salt in drinking water affected the blood pressure of all inhabitants of coastal Bangladesh. Furthermore, we started investigating the factors that control the salt concentration in ponds and tube wells: that knowledge would enable us to predict salt levels in drinking water for different seasons and in case of extreme weather events such as cyclones.
We found that, by drinking just a few litres of water a day, coastal populations in Bangladesh consume a considerable part (up to 200%) of the maximum daily salt intake of 5 grams. As suspected, long-term consumption of salty water was indeed related to higher blood pressure in the population and is expected to increase the risk of cardiovascular disease.
Low salt alternatives
The study revealed, however, that increases in blood pressure could be promptly reversed if people changed to a low-salt alternative water source, such as rainwater or distilled water, for their daily water intake .
While in the UK you could reduce your salt intake by changing your diet, in Bangladesh low-salt drinking water alternatives would help the coastal populations to control their salt intake and therefore keep their blood pressure low. Currently the availability of low-salt water alternatives is however very limited in the area.
The salt in ponds and tube wells was found to be mainly the result of floods caused by storm surges due to tropical cyclones. This is an important finding as it is believed that these events could become more frequent and/or intense in the future due climate change. Furthermore, we found that concentrations of salt on ponds were higher in the dry season due to evaporation of the pond water. A computer model was developed to simulate these effects.
Looking into the future
Currently the computer model and the health findings are combined: this allows us to predict what increases in blood pressure can be expected if – for example – the areas are hit by a cyclone. Furthermore, with the model we can calculate by how much we can reduce salt intake if alternative drinking water sources were introduced in the area. This could for example be rainwater that was collected during the monsoon season and stored underground for use during the dry season. Local solar distillation devices – in which salt is removed from pond or tube well water by exposing it to the sun – also showed great potential for health improvement.
Building on this work, our team is dedicated to continuing our work to find solutions for salinity problems that affect millions of people in coastal Bangladesh and similar vulnerable coastal areas around the world. Currently we are looking at the practicalities of using solar distillation devices at larger scale in salinity affected areas. We are looking at convenience of use and potential sustainability, but also measure quality of the produced water.
Furthermore, working together with local and national policy makers, we are currently estimating how many people fall ill or might even die as result of the higher blood pressures caused by salt people consume with their drinking water. This is essential information for policy-makers and will help them to make well-informed decisions on water supply in these areas to prevent disease and improve overall public health.
1. Khan, A.E., et al., Drinking water salinity and maternal health in coastal Bangladesh: implications of climate change. Environmental health perspectives, 2011. 119(9): p. 1328-1332.2.
2. Khan, A.E., et al., Salinity in drinking water and the risk of (pre)eclampsia and gestational hypertension in coastal bangladesh: a case-control study. PLoS One, 2014. 9(9): p. e108715.
3. Scheelbeek, P.F.D., Hypertensive disorders in salinity prone coastal areas: relevance to global climate change, in Epidemiology and Biostatistics. 2015, Imperial College: London.