Heart
attacks are more common in January
Cardiovascular deaths around the world, such as heart attacks and
strokes, peak in January. Why this is the case has baffled scientists for some
time, but new evidence is starting to unravel the mystery.
Scientists initially thought it had something to do with the cold, but
this proved to be a false start. Researchers at the University of Southern
California examined deaths from heart attacks between 1985 and 1996 in Los
Angeles, a city with a mild winter and a daily minimum temperature that is
relatively constant throughout the year. They found a seasonal variation in heart attacks, with a third
more deaths occurring in January.
The researchers also analysed 1.7m death certificates (2005 to
2008) from seven US locations that ranged from hot to cold. Again they found a
similar pattern of cardiac mortality including heart attacks in these different
locations with a peak in January. These results chime with other studies
conducted across the globe, including
the UK, which uncovered a winter peak in
deaths from cardiovascular disease.
Air pollution
Researchers have also considered air pollution, and here they seem to be
on firmer ground. There is a seasonal
rhythm to air pollution. Nitrogen dioxide levels - a key pollutant in
causing premature deaths in Britain, for example, are at their highest in
January in the large cities. Oxford Street in London is reported to be
the most polluted
street in the world for nitrogen dioxide. In fact, London is so polluted
that in just the first seven days of 2015 and 2016, London already breached its
legal limit on air pollution for the whole of that year.
Flu
Another important trigger for heart attacks is infection. Infections are
high during winter and there is a known link between
the flu virus and cardiovascular disease. The flu virus affects inflammatory
and blood-clotting pathways, which can cause fatty deposits on the artery wall
(plaque) to break loose, leading to coronary artery blockage - the main cause
of heart attacks.
Other risk factors that are also seasonal include high cholesterol, high blood pressure and low
vitamin D levels. Vitamin D deficiency is
associated with increased incidence and risk of heart attacks. Combine these
with the previously mentioned risk factors for coronary death (pollution and
flu), and you have a recipe for disaster.
Beware January mornings
It turns out these circulating risk factors not only have seasonal
variations, but daily ones too. Research shows that they are at high
levels in the morning and low in the evening. So, not only are we more susceptible to
heart attacks in January but there is also a higher incidence of heart attacks between 6am and noon.
12.01.2017
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