Difficulty identifying common odors might signal an increased risk of the thinking, memory and learning problems considered an early warning for Alzheimer’s disease.

The findings are published in the July issue of Archives of General Psychiatry. The work was done by researchers at Rush University Medical Center in Chicago.

They suggest that the simple test might be useful for early diagnosis.

This study involved 589 older adults whose average age was nearly 80.

The focus was mild cognitive impairment, which involves a decline in memory, thinking and learning. Mild cognitive impairment has been linked to later development of Alzheimer disease, a devastating disorder that robs patients of their memories and intellect.

The volunteers were fine when the study began. Once a year for up to five years they took a smell identification test. It involved placing 12 familiar odors under their noses. They were asked to match the odor to one of four choices. Volunteers who correctly identified eight or fewer of the odors were 50 percent more likely to develop mild cognitive impairment than were similar volunteers who correctly identified at least eight odors.

The link remained even when researchers took other factors into account, including whether the person smoked or was a stroke survivor.

The test odors were lemon, cinnamon, banana, onion, black pepper, chocolate, rose, pineapple, soap, paint thinner, gasoline and smoke.