Having a “high normal” serum sodium level in midlife, which reflects less than optimal fluid intake, is associated with an increased risk for left ventricular hypertrophy — a heart failure (HF) precursor — and for HF itself, in older age, a new study suggests.

Compared with middle-aged adults in the Atherosclerosis Risk in Communities (ARIC) study with normal serum sodium, those with levels of 142 to 146 mmol/L were more likely to have left ventricular hypertrophy or HF when they were in their 70s and 80s, independent of other risk factors.  

Natalia Dmitrieva, PhD, a research scientist at the National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, will present the study findings in an eposter on August 27 at the European Society of Cardiology (ESC) Congress 2021.

“Our study suggests that maintaining good hydration can prevent or at least slow down the changes within the heart that lead to heart failure,” she said in a statement from the ESC.

It “suggests that all adults should aim for eight to ten glasses of liquid [daily] and keep salt intake low,” Dmitrieva elaborated in an email to theheart.org | Medscape Cardiology.

However, people should not rely completely on thirst, she cautioned, especially in middle age, when thirst sensation starts to deteriorate. And too much fluid intake can be harmful and even dangerous.

Normal serum sodium is usually defined as 135 to 146 mmol/L, Dmitrieva explained, and this study only involved patients in ARIC with sodium levels in this range, to try to exclude patients with genetic or water-salt balance diseases.

The findings suggest that a serum sodium level of 142 to 146 mmol/L, which would not be flagged as abnormal by a test lab, “can be used by clinicians as a warning sign” for a patient’s increased risk for HF, she noted.

Clinicians should explain this risk to patients and advise them to drink at least 2 L per day. However, people should not try to reduce their sodium levels by drinking more than 2 to 3 L per day, she cautioned, which can be harmful and even deadly, and should consult their doctor.

Watch Hydration

“An important finding of this study is that sodium values considered ‘normal’ may also be deleterious,” Jacob Joseph, MD, director, heart failure program, VA Boston Healthcare System, who was not involved with this study, told theheart.org | Medscape Cardiology in an email .

“These results are similar to studies we have conducted in heart failure with preserved ejection fraction,” noted Jacobs, who is also associate professor of medicine at Harvard Medical School.

Their studies showed a U-shaped relationship between serum sodium values and adverse outcomes, “indicating an ‘optimal’ range of serum sodium value that was narrower than the accepted normal laboratory value range,” he noted.

The study by Dmitrieva et al was observational and the findings would need to be verified in a randomized controlled trial, Joseph pointed out; however, the research “supports the idea that even a high normal sodium level may indicate risk of future heart failure.”

“Hence, patients should pay attention to hydration,” he continued, and “clinicians should not assume that a sodium level of 142 mmol/L is appropriate and should ensure that patients are paying attention to hydration.”

“In today’s busy and stress-filled lifestyle, it is easy to forget about adequate fluid intake,” Joseph added. 

More Than 15,000 Adults Followed for 25 Years

To investigate the relationship between serum sodium, hydration, and future heart failure, Dmitrieva and colleagues analyzed data from 15,792 adults in ARIC who were 44 to 66 years of age at study entry, with serum sodium levels from 135 to 146 mmol/L.

The participants were evaluated over five visits until they reached 70 to 90 years.

They were divided into four groups based on their average serum sodium concentrations at study visits one and two (conducted in the first 3 years): 135 to 139.5 mmol/L, 140 to 141.5 mmol/L, 142 to 143.5 mmol/L, and 144 to 146 mmol/L.

The researchers determined the percentage of people in each group who developed HF and left ventricular hypertrophy at visit five (25 years after study enrollment).

Patients with higher serum sodium levels had a significantly higher risk for HF and left ventricular hypertrophy, after adjustment for other risk factors, including age, blood pressure, kidney function, blood cholesterol, blood glucose, body mass index, sex, and smoking status.

Every 1 mmol/L increase in serum sodium concentration in midlife was associated with 1.20 and 1.11 increased odds of developing left ventricular hypertrophy and HF, respectively, 25 years later.

“More studies are needed to find out what proportion of people with serum sodium 142 mmol/L and higher have this [serum sodium] level because they do not drink enough and will be able to reduce it by making sure they consistently drink 2 to 2.5 L per day,” said Dmitrieva.

“It is likely that for some people, other factors that are related to genetics or diseases affecting water-salt balance could be causing their increased serum sodium levels,” she speculated.

The study was funded by the Intramural Program of the National Heart, Lung, and Blood Institute. The authors and Joseph have no relevant financial disclosures.

European Society of Cardiology (ESC) Congress 2021. Eposter will be presented on August 27, 2021.

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