In a study
of middle-aged and older people with type 2 diabetes, declines in thinking and
memory that are often linked to later dementia happened faster in those who
were depressed compared to those who were not.
than four years, US and Canadian researchers saw significant differences
between depressed and non-depressed diabetes patients in the erosion of a wide
range of cognitive abilities. "Depression appears to be an important risk
factor for dementia and cognitive decline among patients with diabetes,"
Dr Mark Sullivan, professor of psychiatry at the University of Washington and
lead author of the study, told Reuters Health in an email.
diabetes and depression have been found to raise the risk of Alzheimer's
disease and other forms of dementia later in life. But whether depression is a
cause or an effect of cognitive decline remains unclear. Diabetes can damage
organs, especially the kidneys, eyes, nervous system and brain. The disease
also raises a person's risk for having a cardiovascular "event" such
as a heart attack or stroke.
Tests of cognitive abilities
one-quarter of Americans older than age 65 have diabetes, according to the Centres
for Disease Control and Prevention. An estimated 6.5 million Americans in this
age group suffer from depression, according to the National Alliance for Mental
To assess the role of depression in cognitive
decline among older diabetes patients, Sullivan's team looked at data on nearly
3000 people over age 55 with type 2 diabetes and risk factors for
cardiovascular events. On average, participants had had diabetes for about 9
cognitive abilities were given to all participants at the study's beginning,
and again at 20 months and 40 months. One test measured psychomotor speed, or
how long it takes the brain to register a stimulus, process it and respond.
Another looked at the ability to remember words over time. A third test
measured executive functioning, or how the brain uses memories to plan actions,
pay attention and inhibit inappropriate behaviour.
determined whether an individual was depressed, using a 9-question form patients
filled out themselves. More than 2 600 people completed the tests at all three
time points. 62% of these never had scores indicating depression. 18% were
depressed at the start of the study, 16% to 17% were depressed at 20 and 40
months and 5% had scores indicating depression at all three time points.
found that people with symptoms of depression at any point were more likely to
be women, younger, non-Hispanic whites, overweight or obese, and to have higher
blood sugar, total cholesterol and low-density lipoprotein, or "bad"
cholesterol, than others. Yet, the researchers report in JAMA Psychiatry,
depression was linked to greater cognitive decline regardless of other risk
factors. These included age, gender, race, obesity, smoking, alcohol use,
previous cardiovascular events, as well the types of diabetes and heart disease
medications the participants were taking.
study demonstrates that depression accelerates cognitive decline in patients
with diabetes, over a short time frame, in all patient subgroups, and in all
cognitive domains assessed," Sullivan said."Whether depression
treatment will reverse this effect remains to be tested in a separate
randomized trial," he said. "The broad range of cognitive tests used
indicates widespread cognitive problems in performance, memory and speed of
task completion," said Dr Mark Nathanson, director of the geriatric
psychiatry fellowship at Columbia College of Physicians and Surgeons in New
York, who was not involved in the study. He and Sullivan both cautioned,
however, that the role of depression in cognitive decline may be complex.
Depression and dementia
itself is associated with increases in stress hormones, inflammation and other
processes that could directly contribute to cognitive decline, Sullivan said.
But the array of other diseases that often go along with diabetes may also harm
cognition and promote depression. People with diabetes are at higher risk for
vascular dementia, for example, which develops when blood supply to parts of
the brain is cut off, often during a series of unnoticed
"mini-strokes" that cause brain cells to die.
might be an early symptom of vascular disease in the brain, which later
develops into dementia. "My clinical experience is that dementing illness
like Alzheimer's disease and vascular dementia commonly present to the primary
care clinician and mental health professional with depressive symptoms,"
Nathanson, who is also a clinical assistant professor of psychiatry, wrote in
dementia is different from Alzheimer's disease, which causes the majority of
dementia cases in the US and forms characteristic plaques in the brain. One
implication of this study, Nathanson said, is that primary care physicians
would do well to pay attention to and treat depression in people with chronic
illnesses like diabetes.