Low Salt Is NOT Bad For Your Heart

A flurry of recent headlines claimed that following a very low-salt diet could increase the risk of a heart attack or stroke. Don’t start freely shaking on the salt, however – the results are not what they seem.

The study, published in The Lancet, did not look at salt intakes, but assessed sodium excretion in over 133,000 people of whom around 63,500 had hypertension.

Salt and blood pressure

Around one in two people inherit genes which mean their kidneys are less efficient at excreting excess salt. In this widely reported study, however, involving people with hypertension, those with increased sodium excretion in the urine had a greater increase in systolic blood pressure. The link was equivalent to around a 2mmHg rise per additional gram of sodium excreted. For those without hypertension, each additional gram of sodium also increased systolic blood pressure, but by a lesser amount of around 1·22 mmHg.

In people with hypertension, the risk of experiencing a heart attack or stroke over the 4.2 years of follow-up also increased with sodium excretion, so there was a 23% increased risk where sodium excretion was 7 grams per day or greater. What caught the headlines, however, was that the researchers found an 11% increase in risk of cardiovascular disease when sodium excretion was less than 3g per day – whether or not hypertension was present.

BldpressThe important thing to note is that the researchers did not measure dietary salt intake, but used the sodium concentration of urine to approximate dietary salt intakes. Although this method has been validated in Japanese populations, it may not be applicable to people following a more Western style of diet. Why? Because Western diets tend to contain significantly more carbohydrate and sugars which increase circulating levels of insulin.

Insulin has a little-known effect on the kidneys which causes sodium to be retained so, as your carbohydrate intake goes up, the amount of sodium you excrete in your urine goes down. This effect also helps to explain a recent study suggesting that eating too many potatoes increases blood pressure risk.

In the current study, a low sodium urinary excretion might therefore reflect a high sugar diet rather than just a low dietary sodium intake.

More importantly, a low sodium excretion might also reflect worsening kidney disease in people with hypertension, for whom chronic kidney disease is a relatively common complication. In fact, chronic kidney disease is common whether or not you have hypertension, with an estimated one in ten people affected in the United States alone. Reduced kidney funciton is especially likely in those who also follow a high sugar diet and who have metabolic syndrome, type 2 diabetes or who are obese.

Whatever the explanation for the associations the researchers found, please ignore the headlines. When you have hypertension, it is important to continue to follow a low salt regime, and to eat more of the delicious foods that feature on the blood pressure friendly DASH Diet.

If your blood pressure is raised, self-monitoring is key to maintaining good control.

Click here for advice on choosing a blood pressure monitor to use at home.

Image credit: novelo / shutterstock

About DrSarahBrewer

Dr Sarah Brewer MSc (Nutr Med), MA (Cantab), MB, BChir, RNutr, MBANT, CNHC qualified from Cambridge University with degrees in Natural Sciences, Medicine and Surgery. After working in general practice, she gained a master's degree in nutritional medicine from the University of Surrey. Sarah is a registered Medical Doctor, a registered Nutritionist and a registered Nutritional Therapist. She is an award winning author of over 60 popular self-help books and a columnist for Prima magazine.

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4 thoughts on “Low Salt Is NOT Bad For Your Heart

  • Paula

    Hi there, this is a very interesting post about how low salt is not bad for your heart.
    Your post reminds me that we always have to be super careful about what we read and how we react to it. Even though the research you mention was published in the Lancet a highly respected medical journal, it is still vitally important that the information contained in it is properly digested by it’s readers. Thanks for clarifying the research results.

  • Kerry

    Hi Sarah, a very interesting read, makes me think, what I should and shouldn’t be eating. Quite a few years ago I was put on blood pressure medication as my blood pressure was up a bit and my mum had a history of heart problems as well as my dad, I’m also overweight which doesn’t help either. I should be choosing the healthier option and eat correctly, maybe if I lost weight my blood pressure might come down. You have really given me something to think about. Thanks Kerry

  • Guy

    There’s a lot of talk about salt and blood pressure or water retention. It becomes hard to make ourselves an opinion on the subject. I know that salt can affect the blood pressure, and even cause some bulging. It happens to my girlfriend when she happens to eat too salty. But it’s the first time I see that too low salt can lead to a heart attack. How can we know if we are eating too little of it?

    • DrSarahBrewer

      Don’t worry, Guy, it’s very difficult to eat too little salt – you only need 1g per day for optimum health. Most people get 9g per day or more. Those who are actively cutting bac on salt intake get around 3 6o 6g. If you have high blood pressure – or don’t want to develop it in the future – stick to current guidelines to minimise salt intake and you will be fine.