The main source of vitamin D is its
production in skin thanks to the sun. Women are more prone to low vitamin D
than men - and due to differing weather conditions, concentrations vary in
populations across the world.
Vitamin D deficiency is especially common
among the elderly who often have less sun exposure, but it is unclear what
effect the production of vitamin D has on death.
So researchers investigated the
association of vitamin D with deaths from all-causes, cardiovascular diseases
and cancer. They paid particular attention to differences between countries,
sexes and age groups.
Data were taken from seven
population-based cohorts from the US and across Europe. All study participants
were aged 50-79.
Results reported in BMJ-British
Medical Journal
June 2014 show that there was no clear trend of vitamin D by age, but average
levels were consistently lower among women than men. Average levels increased
with education, were lowest in obese individuals and higher among subjects who
exercised.
During 16 years of follow-up, there were
6,695 deaths in 26,018 patients - 2,624 from cardiovascular diseases and 2,227
from cancer.
An association was found between those
with the lowest levels of vitamin D and death from cardiovascular disease - in
people with and without a history of the disease- and deaths from cancer in
those with a history of the disease. No association was found between low
vitamin D levels and deaths from cancer in those without a history of the
disease.
The researchers say this shows an
important role of vitamin D in the prognosis of cancer, although they add
"we cannot exclude reverse causality, that is, that the cancer might have
led to low vitamin D levels." There was also a dose-response relationship
which was unchanged after excluding patients with a history of cardiovascular
disease and cancer.
The researchers say that death from all
causes as a result of low vitamin D has "high public health
relevance" and should be given high priority. They also ask whether levels
of vitamin D in specific countries, different sexes and seasons "should be
considered for defining vitamin D deficiency" due to its varying levels.
They conclude that those with the lowest
levels of vitamin D had an association "with increased all-cause
mortality, cardiovascular mortality, and cancer mortality (in subjects with a
history of cancer)." They say these effects were consistent across
countries, sexes, age groups, and time of the year when blood tests were done and
that "variation by geographic region, sex and season might need to be
taken into account."
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