Association of drinking water salinity with elevated blood pressure and risk of hypertension among coastal and other populations: a systematic review and meta-analysis of observational studies.

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• Higher drinking water salinity was found to be significantly associated with elevated blood pressure and hypertension risk - a major disease and risk factor for CHD, stroke and other diseases.

• Tens of millions of individuals depend on saline intruded groundwater and rising sea levels due to global climate change could be rapidly affecting this.

• Sodium intake via drinking water is not recognised as a hypertension risk factor and current prevention strategies focus primarily on behavioural and metabolic factors revealing a gap in guidelines. Healthcare practitioners working with clients with hypertension should take location and water salinity into account when assessing diet diaries.

Introduction

While the aetiology of cardiovascular disease can be multifactorial, environmental risk factors like drinking water quality are important to consider, particularly given the effects of climate change, with rising sea levels increasing salinity in groundwater and soils. Previous systemic reviews on this topic were limited by lack of quantitative synthesis, narrow focus and incomplete analysis, which this study aimed to address.

Methods

• This was a well-run systematic review and meta-analysis following PRISMA guidelines which aimed to assess the association between drinking water salinity and cardiovascular outcomes.

• 27 observational studies, 15 of which included coastal populations, involving a total of 74,063 participants from 7 countries globally were included in the analysis.

• Impacts on hypertension/systolic and diastolic blood pressure (SBP/DBP) (23 studies), coronary heart disease (CHD) and stroke were assessed.

Results

• Regarding the association between drinking water and BP risk (17 studies; 11 included in the meta-analysis), the pooled mean differences (95% CIs) were 3.22 mm Hg (1.11 to 5.33) for SBP and 2.82 mm Hg (1.44 to 4.20) for DBP.

• 6 studies reported on high versus low water salinity and hypertension risk, with the pooled OR (95% CI) found to be 1.26 (1.07 to 1.48).

• No strong evidence was found in relation to drinking water salinity and risk of gestational hypertension/pre-eclampsia or total CVD events. No study was found which examined the relationship with CHD or stroke risk.

• Further meta-regression analysis showed that high water salinity increased SBP levels in Asian populations only (p = 0.012) and in studies dated from 2000 onwards only (p = 0.002).

• Both SBP and DBP levels were found to be significantly higher in coastal studies (p = <0.05) while higher water salinity increased DBP levels in cross-sectional studies (p = <0.05) and studies published after 2000 showed significantly stronger associations between drinking water salinity and hypertension risk.

Conclusion

Increased drinking water salinity was found to be significantly associated with higher levels of SBP and DBP, and hypertension risk, especially among those in coastal areas.

• Taking a client’s geographical location and drinking water quality into consideration is important, particularly for those with elevated blood pressure/hypertension.

• Dietary sodium exposure comes in different forms including from food and drink which must be fully assessed.

• Mechanistically it is well established that higher sodium intake can affect vascular health via reducing endothelial nitric oxide, increasing vascular stiffness and increasing water retention leading to higher blood volume/cardiac output and kidney function pressure. These mediators must be considered when creating a tailored plan, particularly for those with renal insufficiency.

• There was a lack of evidence found on the association of drinking water salinity and CHD and stroke risk reflecting a gap in available research.

• Long-term drinking water exposure studies are needed as most studies relied on a single assessment of exposure.

• Greater risk was observed for Asian populations which may be explained by differences in exposure levels such as cooking methods. Therefore, research of non-Asian coastal populations, such as sub-Saharan Africa and small island nations, is needed.