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."
For more information
Rob J. W. Arts, Bastiaan A. Blok, Reinout van Crevel,
Leo A. B. Joosten, Peter Aaby, Christine Stabell
Benn, and Mihai G. Netea.
Vitamin A induces inhibitory histone methylation
modifications and down-regulates trained immunity in
human monocytes.
J. Leukoc. Bio.l July 2015 98:129-136;
doi:10.1189/jlb.6AB0914-416R
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