Blood pressure experts put salt ‘controversy’ to bed
Leading researchers in salt and blood pressure refute misleading reports that aim to cast doubt on the evidence
Two articles written by WASSH Chairman, Graham MacGregor, along with WASSH members Norm Campbell, Franco Cappuccio, Feng He, and other expert peers have refuted the arguments against salt reduction as a public health strategy. Some scientists, food industry representatives and pharmaceutical companies have put forward evidence suggesting that sodium (a part of salt) should not be reduced at population level, even though there is a reliable body of research showing that it is one of the most cost-effective measures for saving lives.
The authors explain in detail how: “Inappropriate research methodology, lack of rigor in research, conflicts of interest and commercial bias, questions of professional conduct, and lack of policies to protect public interests are likely to contribute to the controversy about reducing dietary sodium”.
Read the discussions:
- Dietary Sodium 'Controversy'—Issues and Potential Solutions, published in Current Nutrition Reports, 19 April 2021, details the nature of the campaigns against salt reduction and offers some solutions.
- Salt reduction to prevent hypertension: the reasons of the controversy, published in the European Heart Journal, 20 April 2021, details the flaws in the studies that suggest low salt intakes are bad for health. The full paper is available on request.
The evidence for salt reduction
Approximately a third of cases of high blood pressure worldwide are caused by high dietary sodium (part of salt), making sodium the leading dietary risk factor for death and a major cause of disability. Reviews of all the relevant evidence clearly show that eating less salt lowers blood pressure and the risk of diseases including heart disease and stroke.
Governments around the world have set salt reduction targets to reduce the salt added to food to lower blood pressure at a population level. This is one of the most cost-effective ways to improve health and has been labelled a “best buy” by the World Health Organization.
Despite this, there is still the occasional headline claiming that the benefits of salt are controversial. One reason for this is a number of low-quality studies showing a J-shaped relationship between sodium intakes and disease – suggesting salt raises disease risk at low intakes as well as high.
Health organisations have expressed concern about low-quality research led by a small number of highly vocal scientists, and conflicts of interest from the food industry and pharmaceutical companies. These studies are used to create an aura of doubt and controversy to slow salt reduction programmes.
Refuting the controversy
The article in Current Nutrition Reports details the authors’ concerns over flawed research and the campaigns against salt reduction as a public health policy:
(1) Use of inappropriate research methods and lack of rigor in research. For example, estimating sodium intake using one-off urine samples or dietary recall which are unreliable methods.
(2) Conflicts of interest with, or biases for, commercial organizations. For example, some conflicts of interest have not been disclosed and some studies have been funded by the food industry.
(3) Lack of public access to data supporting the research. Some studies have data that are not in the public domain, meaning the results cannot be easily independently verified, and at times have been found to be incorrect.
(4) Scientific and professional conduct in publishing research which at times has not been properly reviewed.
(5) Journal responsibility in publishing low-quality controversial research and inadequate review processes.
(6) Grants, research and ethics committee approvals for inappropriate study designs and methods.
(7) Health and scientific organization issues. Some organisations that support sodium reduction host debates on the subject, giving a platform to organisations presenting poor research and misleading views. Some scientists against sodium reduction also attain high-level positions in major organizations where they then advocate against sodium reduction policies.
(8) Lack of government oversight. Governments have allowed polices to be delayed or deterred by industry lobbying.
The authors offer several ways to raise standards and protect public health policies, for example:
- Disclosing potential conflicts of interest with the pharmaceutical industry, which profits from treating CVD, when publishing research.
- Opponents of public policy should be held accountable, in the same way the tobacco industry has been held accountable.
- Academic organizations should have strict guidelines on receiving research funding for work that oppose important public policies.
- Academic institutions should ensure research methods have a full scientific and ethical review.
- Journals should not publish papers where the data is not publicly accessible for verification, and editors should require documentation of funding and ethical and scientific review.
Professor Graham MacGregor added: “Opponents of sodium reduction often use low-quality research methods prone to spurious results with data that is not easily accessible for independent review. Science is a continual search for truth, and public health policies must be based on truth. Scientists, journal editors, academic institutions, funding bodies and governments have a responsibility to uphold these standards not only for public trust but for public health.”