WHAT WAS CLAIMED
The largest ever blood pressure study found people who consumed more salt had lower blood pressure.
OUR VERDICT
False. Experts have never heard of a large study with this finding, while a similar study found those who consumed more salt had higher blood pressure.
AAP FACTCHECK - Claims the "largest study ever" of its kind found people who ate more salt had "better" blood pressure are inaccurate, despite assertions in a viral video.
Experts told AAP FactCheck they'd never heard of a study with such a finding, while a study with similar attributes reached the opposite conclusion with regards to high blood pressure.
The Facebook video features chiropractor and podcaster Bryan Ardis, who has made other claims which have been fact-checked by multiple outlets.
He discusses a supposed 2016 study published in the Lancet medical journal by researchers at Tel Aviv University, claiming "it was the largest study ever done on high blood pressure".
"And they found – 49 countries, 500,000 people – that the individuals who consumed the most salt every single day had the best blood pressure readings and the most normal blood pressure readings.
"And all of the individuals who consumed three times the amount the FDA [US Food & Drug Administration] tells you you should consume every day, every person around the world that consumed three times that amount, had better blood pressure readings than anybody who took the FDA readings."
In a longer version of the clip on YouTube, Mr Ardis adds that the study in question found "the more salt you eat, the lower your risk factor for high blood pressure, strokes and heart attacks is" (seven minutes 27 seconds).
AAP FactCheck was unable to find a study that matched this description. Experts were also unaware of such a study, supposedly the largest ever conducted in their field, and said the claim was false.
A representative for Mr Ardis did not confirm which study he was referring to in the video when contacted by AAP FactCheck.
AAP FactCheck identified a paper with similar attributes, however this didn't find those who ate more salt had lower blood pressure readings.
A 2016 study led by Canadian researcher Andrew Mente, published in the Lancet, included 133,118 (not 500,000) people in 49 countries and looked at the impact of salt intake on blood pressure and other health outcomes. No researchers from Tel Aviv University are listed as being involved in the research.
It used sodium levels in a single urine sample as a measure of salt intake, finding those who consumed more salt had higher blood pressure readings (figure 2, page 7), noting the association was stronger in people with existing high blood pressure.
However, controversially, it noted a link between low salt intake and an increased risk of cardiovascular disease events like heart attack, stroke and death (p7).
It also found consuming higher amounts of sodium, measured at over 7g per day, was only linked with an increased risk of cardiovascular disease events in those with existing high blood pressure.
It questioned whether public health advice to lower salt intake in the general population was warranted.
The American Heart Association (AHA) said the study was "flawed" in a 2016 press release, and criticised its use of one-off urine samples. It added that other factors might explain the supposed link between low salt levels and heart disease.
In another press release, experts from the association said one-off urine samples could vary wildly based on what a person recently ate.
The Facebook video also claims the AHA threatened to pull its funding for the Lancet if it the journal didn't retract the study.
A Lancet spokesperson told AAP FactCheck it doesn't receive funding from the AHA and that there were no articles published in the Lancet that match the details Mr Ardis provided.
A spokesperson for the AHA told AAP FactCheck it does not provide funding to the Lancet or other outside journals.
Other experts criticised the study when it was published. Francesco Cappuccio, a cardiovascular expert at the University of Warwick, said in an Independent article that the use of one-off urine samples to determine salt intake was flawed, and that the study's participants were almost exclusively "sick people" from clinical trials.
An article by Naomi Fisher, a hypertension expert at Harvard Medical School, raised similar concerns about the study, as did a letter published in the Lancet by heart disease researchers.
In an editorial, the Lancet defended its methodology, saying it was "as robust as the data used to advocate reductions to low levels [of salt intake]".
However, it noted there was "no real disagreement that high salt intake is associated with high blood pressure, and most studies indicate that high blood pressure is associated with more cardiovascular events".
Alta Schutte, Kathy Trieu, and Bruce Neal, experts in salt intake and heart disease at the George Institute for Global Health, told AAP FactCheck they'd never heard of any study - by Tel Aviv researchers or otherwise - that found eating more salt lowered, or resulted in "better", blood pressure.
Professor Schutte called the Facebook video "ridiculous", Professor Neal called it "completely bizarre" and Dr Trieu said the claims "were largely made up" or a "warped" reading of the Mente et al study.
Prof Neal said the link between sodium and blood pressure was "unequivocal" and shown in more than 100 randomised trials.
A Cochrane Review of randomised clinical trials found reducing salt intake reduced blood pressure levels, especially in those with high blood pressure.
Murray Cairns, a professor of experimental pharmacology at the University of Newcastle, told AAP FactCheck that all credible evidence showed salt intake was generally associated with high blood pressure.
High blood pressure can cause a range of heart conditions by forcing the heart to work harder, and can damage arteries and cause aneurysms and strokes, according to the Mayo Clinic.
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