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Hypothesis contradicted? Fatter people get *less* dementia

Researchers were sure fatter people would get more dementia, so they studied two million middle-aged people for nearly a decade but were “baffled to find the exact opposite. Their sample included 45,000 cases of dementia and the obese were 30 per cent less likely to be diagnosed with it.

This contradicts previous studies and was not at all what the researchers expected, so they analyzed the data every which way they could think of but can’t explain the results. Need I say “experts” and “consensuses”?

Scientists at the London School of Hygiene and Tropical Medicine said they were baffled by the results as previous studies have shown that being overweight raises the risk. —Telegraph

Risk factors such as alcohol and smoking made little difference to the results, published in The Lancet Diabetes and Endocrinology.  — Mirror

Dr Qizilbash said the findings held despite attempts to adjust for other causes of dementia and the tendency of obese people to die earlier. “We did a lot of analysis to see if we could explain it but just seems to persist. We couldn’t get rid of it so we’re left with this apparent protective effect,” he said. — The Australian

It’s in the Lancet (and press everywhere– like the BBC, live science, The Australian). I’m posting it for the curiosity, discussion factor, and the sheer thrill of watching the scientific method at work. (Did your government want to add food labels to tell you what to eat?)

There are a lot of possibilities:

1. Being obese prevents dementia.

2. Obese people don’t get diagnosed as easily with dementia.

3. Obese people eat more of some key nutrient and skinny people miss out. (Like perhaps they don’t eat enough chocolate, see this story in The Australian.* I won’t make that mistake 🙂 )

4. The follow up might be too short.

5. Dementia might cause low-BMI (years in advance?) or some factor that causes skinniness goes on to also cause dementia.

6. Some other factor entirely causes dementia, and skinny people are more likely to do it.

The leading author suggests some further avenues to explore:

Qizilbash said some next steps in this research include understanding the influence of weight changes, such as recent weight loss in a person who may not have previously been underweight, on the risk of dementia.

He also wants to look into whether being overweight or obese has an overall positive effect on dementia because someone who weighs more may not live long enough to reap its possible brain-protective effects.

More research is also needed to determine how weight influences the risk of different types of dementia, such as Alzheimer’s disease, vascular disease and Lewy body disease, Qizilbash said.

live science


Qizilbash et al (2015) BMI and risk of dementia in two million people over two decades: a retrospective cohort study Lancet, DOI: http://dx.doi.org/10.1016/S2213-8587(15)00033-9

*Chocolate pills? “Scientists say eating dark chocolate could help to ward off Alzheimer’s and heart disease but it needs to have such intensity that a tablet is being developed for those who cannot stomach the sharp taste.”

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