More than 5 million Americans suffer from Alzheimer's disease, the most prevalent form of dementia which is marked by progressive memory loss. Many factors are attributed to cause the condition, which include nutritional deficiencies, infections and reactions to medications. However, it appears that a person's blood type may also have something to do with the likelihood to suffer from memory loss.

Researchers of a new study have found that individuals whose blood type is the least common also happen to have high risks for memory loss. Only about one in 25 Americans have the blood type AB and these individuals were found to be about twice as likely as individuals with a different blood type to develop memory problems that leads to dementia.

For the study published in the journal Neurology on Sept. 10, Mary Cushman, from the University of Vermont College of Medicine in Burlington, and colleagues gave over 30,000 individuals who were at least 45 years old a series of tests to assess their memory and thinking skills and had them tested again after a little over three years later.

By comparing the blood types of the participants and making adjustments for differences in their gender, race, age and geographical regions, the researchers found that the participants with AB blood types were 82 percent more at risk of suffering from memory impairment compared with the participants with a different blood type.

They also found that those with higher levels of factor VIII, a protein that helps in the clotting of the blood, had 24 percent increased risks of developing cognitive problems. Incidentally, individuals with AB blood have higher average levels of this protein.

"Blood group AB and higher FVIII were associated with increased incidence of cognitive impairment in this prospective study," the researchers wrote. "The association of blood group AB with incident cognitive impairment was not significantly mediated by FVIII levels."

The researchers, however, said that those with type AB blood should not be worried because other factors are known to play a more crucial role in the risks of mental impairment. The participants in the study who suffered from thinking and memory impairment, for instance, were also more likely to smoke as well as suffer from diabetes, heart disease and high cholesterol levels.

"Our study looks at blood type and risk of cognitive impairment, but several studies have shown that factors such as high blood pressure, high cholesterol and diabetes increase the risk of cognitive impairment and dementia," Cushman said.