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New evidence review supports salt reduction in diet guidelines
A new research review finds that eating less salt is linked to lower death rates while vitamin supplements tend to have no effect
A new review of the research around dietary supplements and interventions has shown that few have any effect on diseases of the heart and blood vessels and death. One notable exception was lowering salt intake, which lowered the death rates in people with both normal and raised blood pressure.
The research published in Annals of Internal Medicine this July adds to the body of evidence linking salt intake to serious health problems. The authors noted limitations in the quality of the studies, but said they can be used to help update dietary guidelines.
Why was the research done?
More than half of Americans take supplements but there is little evidence to show that they have any benefit, with a few exceptions, and dietary guidelines don’t recommend them for general use.
The researchers based in the United States set out to examine the evidence around supplements and their effect on death and cardiovascular disease (diseases of the heart and blood vessels such as heart attacks and stroke). They also explored dietary interventions – specific changes to diet made as part of studies, such as eating less salt or fat.
What did they do?
The researchers collected together all the systematic reviews – a thorough and high-quality type of review which looks at all the current evidence – on the topic. They also looked at recent randomised controlled trials – the best type of research trial where people are given an intervention, such as dietary supplements, and the health outcomes over a number of years, such as stroke or heart attacks.
Only the most robust research was included. The researchers combined the results of all these trials, totalling nearly a million people, to examine the effects of 8 dietary interventions and 16 supplements in turn.
What were the results?
There was some evidence to show that eating less salt lowered the rates of death by any cause in people with normal blood pressure, and death due to cardiovascular disease in people with raised blood pressure (hypertension). When looking at death due to cardiovascular disease alone, it was the only intervention or supplement to have an effect.
Other notable results were:
- Use of omega-3 fatty acids (the type of fat found in oily fish) was linked to lower rates of death due to heart attack and coronary heart disease
- Folic acid supplements were linked to a lower risk of stroke
- Combined calcium and vitamin D supplements were linked to an increased risk of stroke, possibly due to calcium contributing to hardening of the arteries.
- Other supplements and interventions had no real effect and in some cases the evidence was lacking.
Are there any limitations to the study?
There was a lack of evidence was lacking for some supplements and interventions, and none of the evidence was considered high-quality. So this study cannot be considered proof of effect but can add to the current research.
What do the results mean?
Before now salt has been clearly linked to blood pressure, and blood pressure has been clearly linked to various illnesses. But there is less evidence linking salt directly to ‘end points’ such as a heart attack or stroke.
This research adds to the evidence that lowering salt is an important part of a healthy diet to prevent cardiovascular disease. It also supports a role for omega 3 fatty acids and folate supplements in the US, but not for supplements in general.
While the strength of the evidence is limited, it is in support of current knowledge and can be used to inform doctors in conversations with their patients and for the development of dietary guidelines.
Katharine Jenner, CEO of Blood Pressure UK, says:
"It’s clear in this study that out of 24 supplements and dietary interventions, reducing salt intake is one of the simplest and most effective methods for preventing cardiovascular disease. Eating more salt quickly raises your blood pressure, while eating less lowers it within a few weeks. So, instead of wasting money on supplements, cutting back on salt and eating a balanced diet with lots of fresh fruit and veg are some of the best things you can do for your health.”