Obesity in middle age is a significant risk factor for developing dementia later in life, but the relationship may be more complicated than we thought.
American and Canadian researchers have now demonstrated that excess weight is associated with a longer life once a diagnosis of dementia has been made.
Considering the number of health problems linked to obesity – from high blood pressure to several cancers – this is a surprising finding.
But the discovery could give experts useful information about how dementia develops and how to slow it down.
The research team analyzed the health records of 4,523 U.S. adults aged 51 and older who did not have dementia at the start of the study period, but who developed it.
Based on their body mass index (BMI) at baseline, they were divided into four groups: normal weight, overweight, class 1 obesity and class 2/3 obesity.
As indicated in the Journal of Alzheimer’s Diseaseover a follow-up period of up to 20 years, those who were of normal weight were significantly more likely to die earlier.
“This does not mean that dementia patients should try to become overweight or obese, because our study was not designed to test that question,” says behavioral scientist Virginia Chang of New York University’s School of Global Public Health.
“But our results suggest that weight status may serve as a useful prognostic signal for survival at the time of dementia diagnosis. They also support the idea that nutrition is a key factor in the health and survival of people with dementia.”
))>Compared to normal-weight people, the overweight group had a 16% lower risk of death during the study period.
For people with class 1 obesity, the risk was 27 percent lower, and for those with class 2/3 obesity, the risk was 22 percent lower.
This was after researchers took into account other important influences on mortality rate, including gender, education level, race and ethnicity, smoking status and other chronic health conditions.
The researchers actively checked for any bias that might have been introduced. For example, they looked at participants’ weight history to see if those in the normal weight range might have previously been overweight and lost weight due to poor health, making them more vulnerable – but the associations still held.
“Since this finding is somewhat counterintuitive, an important question is whether it could simply be an artifact of bias,” says gerontologist Yuan Zhang of Columbia University’s Mailman School of Public Health.
“Our analyzes suggest that the main sources of bias we examined do not explain the survival advantage associated with higher weight.”
The next question is why this counterintuitive link exists.
It’s not clear yet, but researchers think dementia could cause people to skip meals and forget to eat. For those who have more body fat or muscle in reserve, this is potentially less of a problem.
“Nutrition can be a big issue for people with dementia,” says Chang.
“They may suffer from wasting and inability to eat, which may be due to changes in central brain functioning, leading to loss of appetite and initiative, increased energy expenditure and difficulty feeding.”
This is not a completely new idea. The same “obesity paradox” has also been observed in heart and kidney disease.
Further research will be needed, including tracking weight and eating habits over time, to understand why this association exists.
As of yet, there is no evidence of a direct cause-and-effect relationship, so it is unclear whether weight is what keeps people alive longer. However, there is strong evidence that obesity status is a signal worth paying attention to for people with dementia.
“Although the underlying mechanisms are not fully understood, these findings suggest that weight status at diagnosis may serve as a useful prognostic indicator alongside other factors,” the researchers explain.
The research was published in The Journal of Alzheimer’s Disease.
This article was fact-checked by Rachel Garner and edited by Peter Dockrill. Although we are proud of our process, we are only human. If you spot an error, please let us know.
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