The World Health Organisation (WHO) recommends that people consume less than 5g of salt a day, but
global intakes average 10g a day. Excess salt consumption raises blood pressure, which increases the risk of
heart attacks, heart failure and stroke.
Many studies show a linear relationship between salt intake and cardiovascular disease: as salt intake
increases, the risk of cardiovascular disease and premature death increases. But other studies suggest that
the relationship between salt consumption and disease is not linear. They posit that consuming both less
than 7.5g and more than 12.5g of salt per day could lead to an increased risk of cardiovascular disease and
early death. But there are flaws in the methods used in these studies.
We excrete most of the salt we consume in our urine (90 per cent). And there is a large variation in the
amount of salt we consume each day, so the gold standard for measuring salt intakes is to collect urine over
at least three non-consecutive 24-hour periods. Although this is the most accurate way of measuring salt
intake, it is also the most expensive and is more work for both the participant and the researcher.
Some studies have estimated salt intake using spot urine measurements rather than 24-hour urine collection
because it is easier to do, cheaper and less hassle for the participants. Participants only have to provide one
small urine sample from which daily salt intake is then calculated.
A gradual reduction in salt intake across the whole population, as recommended by WHO, remains an
achievable, affordable, effective and important strategy to prevent cardiovascular diseases and premature
death worldwide
The studies that suggest that the relationship between salt intake and cardiovascular disease is not linear
used data from spot urine measurements. This way of measuring, however, is not accurate as it represents
salt intake from a very short period of time and is also affected by the amount of fluid the participant drank
and the time of day the sample was taken. Estimates from spot urine measurements are therefore unreliable
reflections of habitual daily salt intake.
We found that calculating salt intakes from spot urine samples can alter the linear relationship seen between
salt intake and mortality. We analysed data from Trials of Hypertension Prevention, which used the gold
standard method for assessing salt intake (several 24-hour urine measurements) in nearly 3,000 adults with
prehypertension (high normal blood pressure) over periods ranging from 18 months to four years.
When we analysed the data, we found a direct linear relationship between salt intake and the risk of death
down to a salt intake level of 3g a day.
To mimic spot urine sampling, we then applied the formulas developed for these samples on the sodium
concentration of the 24-hour urine samples. The results showed the same non-linear relationship that were
reported in the controversial studies. This implies that their findings could be explained by the method they
used to estimate salt intake, as spot urine measurements are unreliable reflections of habitual daily salt
intake and it also appears that the formulas themselves are problematic.
So the message remains clear: salt reduction saves lives, and the findings from studies that use a less reliable
assessment of salt intake should not be used to derail critical public health policy or divert action.
A gradual reduction in salt intake across the whole population, as recommended by WHO, remains an
achievable, affordable, effective and important strategy to prevent cardiovascular diseases and premature
death worldwide. Even a small reduction in salt intake will have an enormous benefit on people’s health.
Feng He is a professor of global health research at Queen Mary University of London. This article first appeared