Researchers publishing in BMJ Open report the 15% fall in dietary salt intake over the past decade in England is likely to have had a key role in the 40% drop in deaths from heart disease and stroke over the same period. This before the headlines analysis accompanied roundup comments.
Title, Date of Publication & Journal
Salt reduction in England from 2003 to 2011: its relationship to blood pressure, stroke and ischaemic heart disease mortality.
14 April 2014 BMJ Open.
Claim supported by evidence?
The paper does not provide any new evidence for controlling stroke and ischaemic heart disease through population wide reduction in salt intake.
Its conclusion that “salt intake is likely to be an important contributor to the falls in blood pressure from 2003 to 2011” is not based on any new direct evidence, although it may possibly be true.
Data extracted from Health survey for England in 2003, 2006, 2008 and 2011 show a steady reduction in blood pressure.
Data extracted from the national Diet and Nutrition Survey for 2000/2001, 2005/2006, 2008 and 2011 show a decline in salt intake as measured from urine samples.
Data from Office of national Statistics over the period 2003, 2006, 2008 and 2011 show a decline in the death rate from ischaemic heart disease and Stroke.
Although there are parallel trends for these across time, there is no evidence in this study to suggest a causal link between these three observations.
The argument in this paper is simply based on the fact that these three trends continue at a roughly constantly rate in England across the first decade of the 21st century.
However, parallel trends across time are a notoriously low level of evidence.
A secondary analysis, which excluded those on therapy to control blood pressure, does not “investigate the role of salt in reduction in the changes of BP” as claimed. It does not address salt intake at all.
The impact of smoking history is not discussed in much detail. There has been a reduction in smoking prevalence in the past few decades and it is possible this might have been driving some of the changes over time.
The fall in systolic blood pressure “was larger than that which might have been predicted from the meta-analysis of randomised salt reduction trials” by He, Li & MacGregor (2013). One obvious alternative conclusion is that other factors are driving the observed population reduction in blood pressure.
There is very little new quantitative information.
There is no direct linkage between the three sources of information.
It is well known that salt intake alters blood pressure and that controlling blood pressure reduces mortality from heart disease. But this paper adds no new evidence about the size of or veracity of such an assertion.
Before The Headlines is a service provided to the SMC by volunteer statisticians: members of the Royal Statistical Society (RSS), Statisticians in the Pharmaceutical Industry(PSI) and experienced statisticians in academia and research. A list of contributors, including affiliations, is available here.
in this section
filter Headlines by year
search by tag
This website uses only necessary cookies, to improve your experience. Read MoreAccept
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.