20 | New Scientist | 4 April 2020ExerciseWinds are shifting as
the ozone layer healsTHE hole in the ozone layer
above Antarctica is continuing to
recover and it is sparking changes
in atmospheric circulation, the
flow of air over Earth’s surface.
Using data from satellite
observations and climate
simulations, Antara Banerjee
at the University of Colorado
Boulder and her colleagues
modelled changing wind patterns
related to the layer’s recovery,Too much salt may
hit immune systemEATING too much salt may impair
the body’s ability to fight bacterial
infections, according to studies in
mice and in 10 people.
Christian Kurts at the University
Hospital of Bonn in Germany and
his team first showed that mice
given a high-salt diet were less able
to fight kidney infections caused
by E. coli and body-wide infections
due to Listeria monocytogenes,
a source of food poisoning.
“The bacteria caused more
damage before the immune
system got rid of them,” says Kurts.
Next, the team gave 10 healthy
women and men who were 20 to
50 years old an extra 6 grams of
salt a day on top of their normal
diet, in the form of three tablets.
After one week, some of their
immune cells, called neutrophils,
had a greatly impaired ability to
engulf and kill bacteria compared
with before the participants wereDiet^ Atmospheric scienceTHE higher your daily step count,
the lower your risk of death per year,
according to a new analysis – but
the link only goes so far.
We have long been encouraged
to walk as a way of improving
health, but many studies on its
benefits have focused on people in
their early 60s and have sometimes
ignored minority ethnic groups.
A new analysis, by Pedro
Saint-Maurice at the US National
Cancer Institute and his colleagues,
looked at 4840 people who were
representative of the US population
over the age of 40. Between 2003
and 2006, all participants wore
an accelerometer for a week.
The team found that the average
daily step count was 9124 paces,
higher than many previous studies.
That may be because the study
included younger people, thosein less sedentary jobs and more
men, who tend to be more active.
The researchers used 4000 steps
a day as their baseline – easily
achieved by someone who drives to
a desk job. By comparison, the team
found that taking 8000 steps was
associated with a 51 per cent lower
risk of dying per year, and taking
12,000 daily steps was associated
with a 65 per cent lower risk.
But taking more than 12,000
steps didn’t seem to show a further
reduction of mortality risk. Up until
12,000 steps, more paces equated
to a lower risk of dying per year
regardless of sex, race, level of
education, health condition and
whether a person smoked or drank
alcohol. The intensity of the steps
taken also had little to no effect on
the mortality risk (JAMA, doi.org/
dqm4). Jason Arunn MurugesuHigher step count linked to
lower annual risk of death
which is largely thanks to a 1987
ban on the production of ozone-
depleting substances.
Before 2000, in the southern
hemisphere a belt of air currents
called the mid-latitude jet stream
had been gradually shifting
south. Another jet stream, the
subtropical jet responsible for
trade winds, tropical rain belts,
hurricanes and subtropical
deserts, had been getting wider.
Banerjee and her team found
that both trends began to reverse
in 2000. She says they are a
direct effect of the ozone layer
recovering (Nature, doi.org/dqm7).
Alterations in a jet stream may
influence weather via shifts in
temperature and rainfall, which
could lead to changes in ocean
temperature and salinity.
Martyn Chipperfield at the
University of Leeds, UK, says we
had already seen signs that the
ozone hole (pictured, in blue) is
mending, and this study shows
the next step: the effect of that on
the climate. Layal Liverpoolgiven the extra salt to consume
(Science Translational Medicine,
doi.org/dqnr). The researchers
didn’t examine the effect of high
salt intake on the body’s ability to
fight viral infections.
The World Health Organization
recommends that people eat no
more than 5 grams of salt a day to
avoid high blood pressure, which
can cause strokes and heart
disease. In the UK, people eat
8 grams on average, suggesting
many consume as much or more
than the volunteers in the study.
The team thinks that two
mechanisms are involved. First,
when we eat lots of salt, hormones
are released to make the body
excrete more salt. These include
glucocorticoids that have the side
effect of suppressing the immune
system throughout the body.
Second, there is a local effect in
the kidney. Kurts found that urea
accumulates in the kidney when
salt levels are high, and that urea
suppresses neutrophils.
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