Author Interviews, Cognitive Issues, Weight Research / 26.11.2014
Obesity in Midlife Increases Risk of Dementia and Alzheimer’s Disease
MedicalResearch.com Interview with:
Nicolas Cherbuin PhD
ARC Future Fellow - Director of the NeuroImaging and Brain Lab
Centre for Research on Ageing, Health and Wellbeing
Research School of Population Health - College of Medicine Biology and Environment
Australian National University
Medical Research: What is the background for this study? What are the main findings?
Dr. Cherbuin: A number of modifiable risk factors for cognitive aging dementia and Alzheimer’s disease have been identified with a high level of confidence by combining evidence from animal research and systematic reviews of the literature in humans that summarise the available findings without focusing on extreme findings that come about from time to time in research. One such risk factor is obesity for which we have previously conducted a systematic review (Anstey et al. 2011). This showed that obesity is associated with a two-fold increased risk of dementia and a 60% increased risk of Alzheimer’s disease. What was surprising is that this effect was only detectable for obesity in middle age but not old age. This might suggest that the obesity only has an adverse effects on brain health earlier in life and that this effect fades at older ages. This is unlikely because a number of animal studies have shown that the biological mechanisms linking obesity with brain pathology do not disappear with older age but in fact appear to increase. Moreover, human studies show that thinking abilities decline faster in obese individuals. An alternative explanation is that human epidemiological studies investigating this question in older individuals include participants who do not have clinical dementia but in whom the disease is developing. Since dementia and Alzheimer’s disease pathology is associated with weight loss it is possible that estimated effects in humans have been confounded by this issue. Another possible confounder is that older people tend to lose muscle mass (sarcopenia) this may lead to the paradoxical condition in aging where a person has a normal weight but has excessive fat mass. Since it is fat tissue that is linked to risk to cerebral health it may have led to the apparently contradictory findings that obesity may not be a risk in older age. It is therefore of great interest to clarify whether obesity in early old age in individuals free of dementia is associated with poorer cerebral health. The hippocampus is one of the structures most sensitive stressors. Because obesity is known to lead to a state of chronic inflammation which is deleterious to the hippocampus, it was a logical structure to investigate. Moreover, the hippocampus is needed for memory function and mood regulation and is directly implicated in the dementia disease process.
This study investigated 420 participants in their early 60s taking part in a larger longitudinal study of aging taking place in Canberra, Australia and who underwent up to three brain scans over an 8-year follow-up. These individuals were free of dementia and other neurological disorders. Associations between obesity and shrinkage of the hippocampus were investigated with longitudinal analyses which controlled for major confounders.
The main findings were that overweight and obese participants had smaller volume of the hippocampus at the start of the study. In addition, the hippocampus shrunk more in these individuals over the follow-up period.
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