Pumpkin pie, sweet potatoes and many other holiday favorites are rich in vitamin A, a nutrient essential for good health. Now a study by Agricultural Research Service (ARS) nutrition scientists has shown, for the first time, that high levels of vitamin A can suppress development of type 1 diabetes in laboratory mice prone to that disease.

Type 1 diabetes, which affects more than 750,000 Americans, occurs when the immune system mistakenly attacks and destroys the pancreas' insulin-producing beta cells. Scientists already know that vitamin A and antioxidants—such as those in the freeze-dried grape powder also tested in the study—can regulate the immune system.

However, apparently no one had shown the suppressive effect of either vitamin A or grape powder on type 1 diabetes in either lab mice or humans, according to ARS physiologist Charles B. Stephensen.

He collaborated with molecular biologist Susan J. Zunino for the investigation, conducted in their laboratories at the ARS Western Human Nutrition Research Center in Davis, Calif. They reported their findings earlier this year in the Journal of Nutrition.

Blood sugar levels of the 45 mice in the experiment were taken regularly to determine onset of diabetes. At about seven months, only 25 percent of those mice eating a high-vitamin-A feed, and 33 percent of those eating grape-powder-enriched feed, had developed type 1 diabetes, while 71 percent of those on non-enriched feed had became diabetic.

Differences in levels of a protein called tumor necrosis factor-alpha, or TNF-alpha, linked in other studies to type 1 diabetes, were notable. TNF-alpha production by immune cells of mice fed the vitamin A- or grape-powder-enriched feed was significantly lower than that in cells of mice fed standard feed.

The study is part of ongoing research at the nutrition center to discover more about the potential of vitamin A and other nutrients to help prevent diabetes, cancer, asthma and other diseases of the immune system.

ARS, the U.S. Department of Agriculture's chief scientific research agency, and the National Institutes of Health of the U.S. Department of Health and Human Services funded the research.