Teenagers with type 1 diabetes may have a tougher time managing their blood sugar on days when they are feeling angry or down, a new study suggests.

The findings, published in the Annals of Behavioral Medicine, suggest that emotions may affect teens' blood sugar control by making them less confident in their ability to manage their diabetes.

For the study, Katherine T. Fortenberry and colleagues at the University of Utah in Salt Lake City recruited 62 subjects between 11- and 16-years old with type 1 diabetes, an autoummunne disorder that res caused by an abnormal immune system attack on the body's insulin-producing cells. People with the disease have to take daily insulin injections, closely monitor their blood sugar levels and be careful about their diets to avoid sugar highs and lows.

Teens in the study kept a daily diary for two weeks, detailing their mood and confidence in their ability to manage their diabetes.

In general, Fortenberry's group found, the teenagers' blood sugar levels were more likely to be near-normal on days when they were happy or excited.

On days when they were sad or angry, their sugar levels tended to be higher, the researchers report in the Annals of Behavioral Medicine.

The teenagers' self-confidence in their diabetes control seemed to explain the link, Fortenberry's team found.

They note that teenagers who stay positive in the face of managing the disease may be more likely to take all the steps they need to keep their blood sugar in check. Helping teenagers to manage their emotions, the researchers write, may have "important implications" for their lifelong diabetes control.