is known to lower blood pressure, but now a team of British researchers has
figured out why.
What they found is that nitric oxide stored in the top layers of the skin
reacts to sunlight and causes blood vessels to widen as the oxide moves into
the bloodstream. That, in turn, lowers blood
"This is an unexpected finding, in that the skin has not been
considered to be involved in blood pressure regulation," said lead
researcher Martin Feelisch, a professor of experimental medicine and integrative
biology at the University of Southampton.
Feelisch said he thinks – if this finding is confirmed in further research – exposure to ultraviolet light might help reduce the risk for heart
disease. "That's where it becomes interesting," he said.
A mild effect
Among people with normal blood pressure, the effect of ultraviolet light is
modest – a drop in blood pressure of between 2 and 5 millimetres of mercury
(mmHG), Feelisch said.
"This is a mild effect," he said. "But if you repeat this
study in people with high blood pressure, I would predict you will see a more
Avoiding sunlight or using sunblock constantly out of a fear of skin cancer
could be a new risk factor for heart disease, Feelisch said.
He isn't suggesting that people should sunbathe or use tanning beds in hopes
of lowering blood pressure, however. What he recommended is spending a moderate
amount of time outdoors.
"People are dying of skin cancer, and sunlight is the only known risk
factor that contributes to skin cancer," Feelisch said. "We are fully
aware of that and don't say everyone should get as much sun as possible. There
is a very real risk – but so is the risk for [heart] disease. One of the main
contributors to the disease is high blood pressure."
Excessive exposure to sunlight carries the risk of developing skin cancer,
Feelisch said, but too little might increase the risk of heart disease.
However, more people die from heart disease than from skin cancer, he said.
"We believe current public health advice, which is dominated by
concerns of skin cancer, needs to be carefully reassessed," he said.
"It's time to look at the balance of risk for skin cancer and
The report was published in the Journal of Investigative
Dr Gregg Fonarow, associate chief of the division of cardiology at the
University of California, Los Angeles, David Geffen School of Medicine, said
high blood pressure is a major risk factor for stroke and kidney disease, in
addition to heart disease.
Blood pressure levels
That blood pressure levels are higher during winter and further away from
the equator has been known, but the reasons behind these observations had not
been entirely clear, he said.
"This new study finds that UV light exposure to the skin induced nitric
oxide release and modestly lowered blood pressure, suggesting that this may
play a role in modulating blood pressure," said Fonarow, a spokesman for
the American Heart Association.
Further studies are needed to determine the degree to which varying levels
of light exposure might play a role in regulating blood pressure and reducing
heart risk, he said.
For the study, Feelisch and his colleagues exposed 24 people with normal
blood pressure to ultraviolet A radiation equal to spending about 30 minutes in
They found that the exposure widened the blood vessels, which significantly
lowered blood pressure and changed the levels of nitric oxide in the blood.
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