When people with type 2 diabetes also struggle with depression, their odds for a third worrisome condition - dementia - goes up markedly, a new study suggests.
Specifically, patients with type 2 diabetes are twice as likely to develop dementia three to five years after being diagnosed with depression compared to non-depressed people with diabetes, researchers found.
"We've known for years that diabetes is a risk factor for dementia," explained study lead author Dr Wayne Katon, a professor and vice chair of the department of psychiatry and behavioural sciences at the University of Washington's School of Public Health in Seattle. "In fact, having diabetes itself probably doubles the risk for dementia," Katon added.
"We've also known that a very common accompanying condition with diabetes is depression," Katon said. "Some 20% of diabetics have depression. And now our data suggests that if you do have depression in addition to diabetes, it actually doubles again the already increased risk for dementia that diabetic patients face."
However, the study authors noted that the absolute risk of dementia for any one person with depression and diabetes remains relatively small - about one in 50.
Katon and his colleagues published their research, which was supported by the US National Institutes of Health-funded Diabetes & Aging Study and the Diabetes Study of Northern California, in the online edition of Archives of General Psychiatry.
The authors noted that depression and diabetes are among the most prevalent health issues facing American seniors.
What's more, each of the two conditions seem to independently raise the risk for developing the other: being diabetic bumps up the likelihood of becoming depressed, while being depressed boosts the risk for developing diabetes.
In the new study, the researchers focused on more than 19,000 California residents with diabetes between the ages of 30 and 75.
Nearly one in five of the patients were also deemed to be experiencing "clinically significant" depression, the authors noted.
After monitoring for the onset of dementia over a three- to-five-year period, the research team found that just over 2% of those who had both diabetes and depression went on to develop one or more forms of dementia, including Alzheimer's disease.
By contrast, just 1% of patients who had diabetes alone ended up developing dementia during that period.
But the authors also noted that many of the things that can boost the odds for depression among diabetic patients, such as eating a poor diet, maintaining a sedentary lifestyle and/or smoking, are modifiable behaviours. This means that patients and physicians alike have some clear targets for interventions to lower depression risk, and possibly dementia risk as well.
"So the important thing to focus on here is that there are very effective treatments for depression," said Katon. "And so if you're a diabetic who does have depression it's very important to get it attended to. Just as important as getting your diabetes itself treated."
Dr Robert Friedland, chair of neurology at the University of Louisville School of Medicine in Louisville, Ky., agreed.
"It is not surprising that they should find a relationship between depression in diabetics and a higher risk for dementia," he said. "But I would point out that although both diabetes and dementia have genetic influences, there are also clear things people can do to lower their risk for both. For example, avoiding obesity by eating a relatively low-fat diet and engaging in regular physical exercise can help to prevent both diabetes and depression. And, therefore, dementia as well."
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