The centenarians face numerous problems including health, finance, death of a spouse or loved one, and many suffer from depression that has been under diagnosed.
"Centenarians are still rare, and depression hasn't been studied thoroughly in this group," said Adam Davey, a developmental psychologist in the College of Health Professions at Temple University.
"We've found that it's a very under diagnosed condition among people over 100 years old, yet it's one of the most easily treated forms of mental illness," he added.
The research team led by Davey looked at indicators of depression among 244 centenarians and found that more than 25 percent showed clinically relevant levels of depressive symptoms, yet only 8 percent reported having a current diagnosis of depression.
Davey said that further study was needed to pinpoint the reason for these high levels.
He, however, added that his research suggested a number of factors, including poor nutritional status, urinary incontinence, limited physical activity and past history of anxiety.
"People who suffer from depression tend to have a high risk of mortality, so it's puzzling to see higher numbers among the oldest old," he said.
"Caregivers often focus on the physical part of health. Or, when they look at the mental health of older adults, they focus more on dementia. But depression is important to consider too - it's not just something that younger people suffer from," he added.
The study was presented at the Gerontological Society of America's annual meeting.