Being overweight or obese in midlife and beyond increases the risk for dementia even if there is no history of diabetes and vascular disease.
With 1.6 billion adults around the world being overweight, controlling body weight can help prevent dementia in seniors, the researchers say.
Recent research has shown a link “between midlife obesity and dementia, but for overweight, the association has been controversial,” said lead author Weili L. Xu, MD, PhD, a postdoctoral researcher in the Aging Research Center, Karolinska Institute, Stockholm, Sweden. “But from this twin study, we demonstrated that both overweight and obesity increases the risk of dementia in later life.”
The study was published in the May 3 issue of Neurology.
The research study used data from the nationwide Swedish Twin Registry between the years 1998 and 2001. The twins in this registry were age 65 years and older. 13,723 twins completed cognitive screening tests and 8534 were included in this study.
The protocol included a neuropsychological assessment, including the Mini Mental State Examination (MMSE). Researchers calculated body mass index (BMI) at midlife (mean age, 43.4 years) using self-reported weight in kilograms divided by self-reported height in meters squared and categorized BMI into 4 groups: underweight (BMI < 20), normal weight (20-25), overweight (26-30), and obese (>30).
Dementia was diagnosed in 350 of the 8534 participants (4.1%), including 232 with Alzheimer’s disease and 74 with vascular dementia; 114 (1.3%) had what was considered questionable dementia.
Compared with those without dementia, twins with confirmed or questionable dementia were older; had lower levels of education and current BMI; and were more likely to have diabetes, stroke, and heart disease.
The study showed a strong link between dementia and midlife BMI. In the model adjusted for age, sex, education, diabetes, hypertension, stroke, and heart disease, both overweight and obesity at midlife were associated with increased dementia risk compared with normal BMI.
In this study, 29.8% (2541) of the twins were overweight or obese at midlife, a percentage much lower than the over 50% who are currently considered overweight or obese in the United States and Europe. This, said Dr. Xu, is because the data are from 30 years ago, before the global obesity epidemic.
In a matched case-control analysis of 137 dementia-discordant twin pairs a high BMI equaled a higher rate of dementia.
Because twins share the same genes and early life environment, these 2 factors might help explain the link between body weight and dementia, said Dr. Xu.
In the case of only 1 twin developing dementia, that sibling might have been exposed to a trigger in early life that turned on a gene that increased the risk for obesity or dementia, she added. Dr. Xu and her colleagues have shown that the FTO gene, for example, is associated with both obesity and Alzheimer’s disease.
In addition to the contribution of genes, the link between body fat and dementia could involve a vascular pathway, said Dr. Xu. “High body fat is associated with diabetes and vascular disease, which in turn are related to dementia risk.” However, this study controlled for lifespan vascular disease, suggesting that the pathway may be nonvascular.
If that’s the case, the pathway may involve metabolism. High adiposity is associated with an altered metabolic status, including hyperglycemia, hyperlipidemia, and high blood pressure. This can contribute to the metabolic syndrome, which other studies have linked to cognitive decline, said Dr. Xu.
Or, the association could also involve a hormonal pathway or inflammation, said Dr. Xu. “Adipose tissue is the largest endocrine organ and it secretes inflammatory cytokines and growth hormones such as interleukin-6 and C-reactive protein, and also leptin, which is associated with obesity.”
Whatever the mechanism, the important message is that overweight and obese people need to lose weight. Dr. Xu emphasized that even though the study looked at midlife body weight, “it’s never too late” to shed excess pounds.
She added that physical activity can reverse the risk for dementia due to obesity. “This is part of our ongoing study, but preliminary results already show that if you do more physical activity, you can reduce your risk of dementia.”
John Hart, MD, professor of neurology, Southwestern Medical Center, Dallas, Texas, and member of the American Academy of Neurology, emphasized that the study shows correlation between obesity and dementia and does not prove cause and effect.
As for the contribution of environmental factors, Dr. Hart agreed that twins share genes, but they don’t necessarily share the same experiences that might trigger a genetic reaction. For example, one twin may have had a severe infection or a head injury that the other twin didn’t.
This is just one more wake up call to stay fit and eat right.
Excerpts courtesy of http://bit.ly/jMOFVc
Image courtesy of http://bit.ly/jwm4lE
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