Although vitamin A supplementation can have
profound health benefits when someone is deficient, new evidence is emerging to
show that vitamin A supplementation above and beyond normal levels may have
negative health consequences. A new research report published in the July 2015
issue of the Journal of Leukocyte Biology
may help to explain why too much vitamin A can be harmful. Too much vitamin A
shuts down the body's trained immunity, opening the door to infections to which
we would otherwise be immune. This study adds to the arguments that vitamin A
supplementation should only be done with clear biological and clinical
arguments. Furthermore, it also suggests that low vitamin A concentrations in
certain situations may even be "normal."
"This study helps to explain the mechanisms
of anti-inflammatory effects of vitamin A and by doing so opens the door to
identifying novel ways to modulate the immune response and restore its function
in situations in which it is dysregulated," said Mihai G. Netea, M.D.,
Ph.D., a researcher involved in the work from the Department of Internal
Medicine at Radboud University Medical Center in Nijmegen, The Netherlands.
To make this discovery, Netea and colleagues
stimulated immune cells, isolated from volunteers, with Vitamin A and saw that
the cells produced fewer cytokines, key proteins that help ward off microbes,
upon stimulation with various mitogens and antigens. Furthermore, the cells
were also stimulated with various microbial structures, which resulted in
long-term activation or training of the cells. When the same experiments were
performed in the presence of vitamin A, the microbial structures were no longer
able to activate the immune cells.
"The interface of nutrition and immunity is
an area of considerable importance, especially in an age when dietary
supplements and vitamins are quite common," said John Wherry, Ph.D.,
Deputy Editor of the Journal of Leukocyte Biology. "These new
findings shed light on an importance balance in vitamin A levels for optimal
immunity. These studies have implications for how we think about daily
vitamins, but also for the developing world, where improving diet could have
dramatic benefits on how the immune system is trained to respond to different
infections."
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