Midlife overweightness linked to higher dementia risks
The more overweight you are as an adult, the greater your chances of being diagnosed with some form of dementia after the age of 65, according to a meta-study.
Loose ends abound when it comes to solving the entire riddle of dementia, but medical researchers have grown more certain that being overweight in midlife increases the odds of Alzheimer’s or other forms of dementia later in life.
Swedish, French and Dutch researchers have analysed 27 studies which have focused on this connection in the decade of 2003–2013. The researchers define midlife in this context as people aged 38 to 60.
“Our main conclusion is that being overweight in this age group gives a higher risk of dementia after the age of 65, as compared to those of normal weights,” says Deborah Gustafson, a researcher at the University of Gothenburg’s Sahlgrenska Academy.
By overweight, the researchers mean a BMI of over 25. The risk of dementia appears to be higher the greater a person’s BMI, according to Gustafson. In other words, obesity (BMI over 30) lifts the risk even higher.
She is a co-author of the meta-analysis, based on data for over 120,000 persons in Europe, Asia and the USA. This study of over two dozen other studies was recently published in the Journal of Alzheimer’s Disease.
Elevated BMI first associated with lower risk
Jostein Holmen, a professor of social medicine at the Norwegian University of Science and Technology (NTNU) in Trondheim, finds the main conclusion of this new meta-study thought-provoking.
“This is especially in light of the global obesity epidemic we are experiencing. Although the 27 studies don’t all show the same things, the pattern is clear. As far as I can see the results are well founded,” says Holmen, whose areas of research include dementia.
Yet the new study shows that tipping the scales too heavily appears to have a different effect among people over 65 than among those who are younger.
“Among the elderly we see that obesity has a protective effect. Dementia among these is more often linked to being underweight – having a BMI below the norm. An explanation could be that early symptoms of dementia contribute to weight loss, for instance that neurological changes in taste and smell have an effect on eating habits,” says Gustafson.
No cause and effect shown
Jøran Hjelmesæth, a professor at the University of Oslo and head of the Morbid Obesity Center at Vestfold Hospital, thinks the meta-study has been thoroughly implemented. That said, he finds one important point of contention.
“The article concludes that there is a real link between overweightness in midlife and dementia later on. But it doesn’t show any causal relationship between these two factors. For example, the report refers to no studies which show that losing weight lowers the risk of dementia later on. But that is because no such studies exist,” he says, adding that this is an aspect which calls for more research.
Hjelmesæth does think that such meta-studies are helpful.
“But in this case, the results are undermined somewhat because the researchers have not carried out a systematic review of literature on the subject. They have studied the publications, but have not followed the clear guidelines demanded for systematic reviews,” he says.
Jostein Holmen agrees that systematic reviews are the gold standard in research.
“But here I don’t consider this a strong counterargument, as this is a relatively new field of research,” he explains.
One of several risk factors
The first study indicating a link between an elevated BMI in midlife and Alzheimer’s or dementia later in life was published in 2003.
Gustafson stresses that midlife overweightness and obesity comprise just one of several risk factors for dementia.
“Other factors include hypertension, high cholesterol and cardiovascular diseases,” she says.
Gustafson also says that the major findings in the report indicate the need for clarifications and she has no doubts that the relationship between dementia and overweightness is complex.
Professor Holmen concurs that scientists still have a lot to learn about the causes of dementia.
“But what might be the most exciting thing in this sphere right now is that several studies have been made indicating that it’s possible to prevent or delay the development of dementia,” he says.
Read the Norwegian version of this article at forskning.no
Translated by: Glenn Ostling
- T. A. Emmerzaal et. al.: Decade of Body Mass index, Alzheimer’s Disease, and Dementia. Journal of Alzheimer’s Disease (2014) (Abstract)