High levels of vitamin A may
curb the onset of type 1 diabetes by protecting against
the attack of insulin-producing beta cells, according to
an animal study by American scientists.
Type 1 juvenile diabetes occurs when the infiltration of
activated T lymphocytes and monocytes into the islets of
Langerhans of the pancreas causes the immune system to
destroy insulin-producing beta cells.
It is estimated that type 1 diabetes affects 218,000
people develop type 1 diabetes worldwide annually, of whom
about 40 per cent are children.
It has previously been found that vitamin A and
antioxidants can regulate the immune system. However,
Charles Stephensen, a physiologist for the US Department
of Agriculture's Agricultural Research Service (ARS), said
that no one has shown the suppressive effect of vitamin A
on type 1 diabetes.
His study, published in the Journal of Nutrition,
investigated this effect in mice and found that vitamin A
consumption resulted in lower levels of tumour necrosis
factor-alpha (TNF-alpha), a protein that has been linked
in other studies to type 1 diabetes.
"Because vitamin A deficiency can directly impair
cytotoxic T cell responses, it is plausible that both
vitamin A deficiency and excess can affect the development
of diabetes via different effects on the beta
cell-specific immune response," wrote the authors of the
study.
The study
Forty-five female non-obese mice were used to investigate
the effect of polyphenols or vitamin A, both found to
modulate the immune function, on blood sugar levels.
Three modified diets were prepared. The control diet was
chosen as it has been found to result in 80 to 90 per cent
incidence of diabetes in mice.
Mice in the test group were fed a diet supplemented either
with 1 per cent freeze-dried grape powder or 250 IU
vitamin A/g of food.
Mice were considered diabetic when the blood glucose level
was equal to or greater than 13.9 mmol per litre and were
then killed by carbon dioxide asphyxiation.
After seven months, only 25 per cent of the mice consuming
large quantities of vitamin A and 33 per cent of those
eating diets enriched with grape-powder had developed type
1 diabetes.
In contrast, 71 per cent of those on the non-enriched
control diet had become diabetic.
The researchers noted there were significantly lower
levels of TNF-alpha production by the immune cells of mice
fed the vitamin A or grape powder.
The study's authors concluded: "Dietary intervention with
foods or food constituents may prove to be beneficial in
the prevention and/or management of type 1 diabetes.
Increasing polyphenol or vitamin A levels in the diet may
have profound effects on suppressing inflammatory immune
cells and reducing the oxidative damage in the islets that
contributes to loss of beta cells.
"Furthermore, dietary interventions such as those in this
study may by useful for treatment of other autoimmune and
inflammatory diseases."
The study is part of ongoing research at the nutrition
centre to discover more about the potential nutrients,
such as vitamin A, to help prevent diabetes, cancer,
asthma and other diseases affecting the immune system.
Sources
Journal of Nutrition
2007; 137: 1216-1221
"Diets Rich in Polyphenols and Vitamin A Inhibit the
Development of Type I Autoimmune Diabetes in Nonobese
Diabetic Mice"
Authors: Susan Zunino, David Storms, Charles Stephensen
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