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