Although there are many potential predictors of conversion from mild cognitive impairment (MCI) to dementia, several may be modifiable, new research suggests.
A meta-analysis of 62 studies showed that diabetes and prediabetes increased risk for conversion from MCI to Alzheimer's dementia and all-cause dementia. In addition, metabolic syndrome, low dietary folate, the presence of any neuropsychiatric symptoms, and having depressive symptoms all predicted dementia conversion in patients with various forms of MCI ― whereas consumption of a Mediterranean diet decreased risk.
The factors deemed "potentially modifiable" included diabetes, metabolic syndrome, diet, and neuropsychiatric symptoms.
"I think the core message is that looking after your diet and your physical and mental health is the best way to fight dementia," lead author Claudia Cooper, PhD, MRCPsych, from the Division of Psychiatry at University College London, United Kingdom, told Medscape Medical News.
"My feeling is that those things that appear to prevent dementia are good, common sense things that are good for physical health anyway," said Dr Cooper, adding that it should therefore be "very easy" for clinicians to recommend that their patients incorporate them.
The study was published online February 20 in the American Journal of Psychiatry.
"We don't have any evidence-based interventions for people with MCI, who are a growing group," said Dr Cooper.
"More and more people are being diagnosed...and they are a group that is highly motivated to do everything they can to reduce their chances of getting dementia. So we wanted to see what the best advice to give them was," she added.
The investigators assessed longitudinal observational studies conducted through May 2013 that evaluated modifiable risk factors for dementia. Of the studies chosen, 17 were epidemiologic, and 45 were clinical.
Results showed that having diabetes increased risk for Alzheimer's dementia in individuals who already had amnestic MCI and increased risk for any-cause dementia in those with any-type or nonamnestic MCI (pooled odds ratio [OR], 1.65; 95% confidence interval [CI], 1.12 - 2.43).
However, in one study, treating diabetes significantly decreased the risk for Alzheimer's dementia vs not treating it, "suggesting this risk may be modifiable."
"Our review shows that diabetes remains an important predictor of dementia in people with MCI and suggests it may be helpful to ensure this is detected and treated," write the investigators.
Prediabetes predicted conversion from any-type MCI to all-cause dementia, and metabolic syndrome predicted conversion from amnestic MCI to all-cause dementia.
Patients adhering to a diet low in dairy and meat products and high in fish, fruits, and vegetables were less likely to progress from amnestic MCI to Alzheimer's dementia. There was also a decreased risk of progressing from any-type MCI to all-cause dementia in those with higher serum folate levels.
The presence of neuropsychiatric symptoms predicted conversion to all-cause dementia from any-type MCI in four clinical studies (pooled OR, 3.11; 95% CI, 1.38 - 7.02). However, level of symptoms was not a predictor.
"Neuropsychiatric symptoms may be etiologic for dementia, for example through neuroendocrine axis activation, or they may interact synergistically with a biological factor, such as genetic predisposition," write the researchers.
"Either of these putative relationships suggests that treating neuropsychiatric symptoms could theoretically delay dementia."
Although higher levels of depressive symptoms predicted progression from any-type MCI to all-cause dementia in the epidemiologic studies examined, "the evidence is inconsistent" in clinical studies regarding progression from amnestic MCI to either Alzheimer's or any-cause dementia. Anxiety and apathy were also found to be inconsistent predictors.
Heavy alcohol use predicted conversion to dementia from any-type MCI.
Hypertension, hypercholesterolemia, homocysteine serum level, smoking, moderate use of alcohol, and level of education did not significantly predict conversion from MCI to dementia.
"While the onset of MCI may be delayed in those with more education, our review indicates that progression to dementia is not delayed once MCI is diagnosed, consistent with cognitive reserve theory," write the investigators.
Although they note that the reviewed studies do not imply causation for any of the factors, "in the absence of effective MCI treatments," the results suggest that managing components of diabetes, metabolic syndrome, and dietary interventions "are logical targets for future trials."
"I thought it was interesting that the investigators weren't necessarily looking at the linkage of these different lifestyle components and risks of [MCI] or dementia," Heather Snyder, PhD, director of medical and scientific operations at the Alzheimer's Association, told Medscape Medical News.
"They were looking at linkages in terms of, if you have [MCI], what is the progression to full-blown dementia? And that's a little bit of a different take than we typically see," she said.
"However, at the end of the day, this is still a review, and much of their suggestions, conclusions, and summary really needs those larger-scale studies to be done to confirm their findings about whether these linkages are real and whether they are causative."
Dr Snyder, who was not involved with this research, noted that contrary to the review's finding about smoking, several studies have "consistently shown" that active smoking is a risk factor for developing MCI or dementia in later life.
She also noted that several past studies have examined whether depression increases risk for later-life dementia.
"There's been a big question as to whether it's actually a risk factor, or is it a sign of changes that might be happening in the brain that may be linked to later-life changes associated with Alzheimer's disease? And I think those are questions we don't know," said Dr Snyder.
"Trying to understand what these relationships actually look like, we really do need that large-scale, Framingham type of study that follows a large number of people over time and looks at lifestyle, depression, and cardiovascular factors and how their interactivity might be impacting overall brain health," she said.
"I think the take-home message is that we can't draw any specific conclusions from this study, but we can talk about linkages between cardiovascular health and brain health as we age," Dr Snyder concluded.
Dr Cooper and two of the remaining three study authors report no relevant financial relationships. Coinvestigator Constantine Lyketsos, MD, has reported several potential conflicts, which are fully listed in the original article.
Am J Psychiatry. Published online February 20, 2015. Abstract
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Cite this: 'Common Sense' Lifestyle Factors May Delay Dementia Onset - Medscape - Mar 05, 2015.