Obese middle-aged men and women are at greater risk of cognitive decline and dementia. That much is known.

But this link is not well established among obese seniors. And in fact, some studies even suggest being overweight in old age protects against dementia – while being thinner than normal is detrimental!

This odd riddle needed unraveling, so scientists from the Republic of Korea sought to do just that. . .

Underweight Men – Watch Out!

Until now, studies that have looked into late life obesity and dementia tended to be small and didn’t take into account lifestyle and heart disease risk factors known to influence both weight and thinking ability.

So the Korean scientists began by analyzing data on a sizable number — 67,219 people aged between 60 and 79. Their body mass index (BMI) was measured in 2002 and again two years later.

The researchers then gathered data on lifestyle factors to see if the participants smoked, drank alcohol frequently, were couch potatoes, or had a lower socioeconomic status. There’s a reason the scientists looked at these variables: They are all linked to dementia.

Likewise they took into account other established risk factors for dementia such as high blood pressure, congestive heart failure, diabetes, and high fasting blood sugar.

After 5.3 years follow up, 11,572 subjects were diagnosed with dementia.

Published in the British Medical Journal’s publication, BMJ Open in May, the findings revealed that participants’ BMI at the start of the study had no influence on their risk for dementia — with one exception.

Men had a significantly increased risk if they were underweight, defined as a BMI of less than 18.5. (a normal BMI is between18.5 and 24.9).

On top of this came another interesting finding. . .

Increases Risk by Up to a Quarter

The researchers found changes in the BMI were significantly linked to dementia in both men and women.

A BMI change of ten percent or more between 2002 and 2004 — whether that change was up or down — raised a person’s dementia risk compared to those who maintained a stable BMI.

For men, the increased risk was large — 25 percent if you put on pounds and 26 percent if you took them off. The figures for women were 17 percent and 15 percent.

The scientists concluded, “Both weight gain and weight loss may be significant risk factors associated with dementia.”

While the results suggest older people should not go on a rapid weight loss diet, the scientists noted that a loss of weight in this group is usually unintended.

Here’s why.

Cause and Effect Can’t be Established

Weight loss could be linked to a pre-existing chronic disease that is itself related to cognitive decline or dementia, such as cancer or liver disease. It’s also possible that weight loss could be an early symptom of dementia. In other words, dementia may be causing the weight loss, not the other way around.

This point was made by Dr. James Pickett, head of research at Alzheimer’s Society UK, who said, “Although this research suggests rapid changes to our weight later in life could increase dementia risk, it’s difficult to distinguish between cause and effect. People with early dementia can often report changes in appetite and diet.”

Since the study was observational, it can’t establish cause and effect. It will take a study with a different design to determine this.

What This Means for Your Own Health

Small changes in weight in either direction are normal. However, any significant change that comes out of the blue, where the cause can’t be pinpointed, should be investigated, as a number of medical conditions need to be ruled out.

I would note that a ten percent change in weight – up or down – is fairly large. Somehow it appears to stress the brain, in ways unknown, and thereby brings on a jump in dementia risk that I sure don’t want for myself.

But it’s a complicated subject, and I’m sure we haven’t heard the last word. Overweight is associated with diabetes and is known to increase cancer risk. Meanwhile being underweight is well known to extend a person’s life by years. I wouldn’t rationalize a gut hanging over the belt with the thought that it’s protecting you against dementia.

For readers who are still relatively young, this should spur you on to reach a healthy weight now and maintain it for life – not too fat, and not thin to the point of being unhealthy. It does look like drastic weight changes after the age of 60 or so can be too stressful.


  1. https://bmjopen.bmj.com/content/9/5/e021739
  2. https://www.sciencedaily.com/releases/2019/05/190520190053.htm

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