September 30, 2006
Alzheimer's Disease Causes Weight Loss Before Diagnosis

Here's another reason to be skeptical of claims that obesity doesn't increase mortality risks.

A long-term study of the elderly has revealed that their average rate of weight loss doubles in the year before symptoms of Alzheimer's-type dementia first become detectable. The finding may be useful to researchers seeking ways to detect and treat Alzheimer's before it causes irreversible brain damage.

The study is the first to confirm in precise detail a link between weight loss and dementia tentatively identified a decade ago. Researchers report in the September 2006 Archives of Neurology that one year before study volunteers were diagnosed with very mild dementia, their rate of weight loss doubled from 0.6 pounds per year to 1.2 pounds per year. The analysis used data from the Memory and Aging Project at the Alzheimer's Disease Research Center (ADRC) of Washington University School of Medicine in St. Louis.

Alzheimer's researchers are working hard to find biomarkers, indicators that can be used to detect the presence of Alzheimer's before clinical symptoms become obvious. Studies at the ADRC and elsewhere have strongly suggested that if Alzheimer's treatments will ever prevent lasting cognitive damage, they may have to be given to patients before memory loss and other disruptions caused by the disorder are evident.

When you read claims that being overweight is not correlated with shorter lifespans keep in mind that a number of illnesses cause weight loss before the illnesses are diagnosed. Cancer can cause weight loss. Unexpected weight loss is sometimes the reason people with undiagnosed cancer go to a doctor and end up with a cancer diagnosis. But cancer is not the only major disease common in old age that causes weight loss. As reported above, even Alzheimer's causes weight loss before diagnosis.

Botton line: People who keep their weight down as a conscious choice are mixed in with people who have lost weight due to illness. So reports which show similar risk of death in the overweight and regular weight are misleading unless they are carefully crafted to control for illness as a cause of weight loss.

A couple of recent studies did attempt to control for illness as a cause of weight loss. They used weight of their subjects before the subjects reached old age. This allowed them to reduce the bias caused by weight loss due to undiagnosed illnesses. They found that being overweight really does shorten life expectancy. See my post Two Studies Find Being Overweight Shortens Life Expectancy for the details.

Share |      Randall Parker, 2006 September 30 09:42 PM  Brain Alzheimers Disease


Comments
Nancy said at October 1, 2006 9:22 AM:

Weight loss doesn't CAUSE Alzheimer's. Correlation is not causation. Finding weight loss among those who later display Alzheimer's symptoms does not establish a causal connection between the two. Further, even if there were a causal relationship, you cannot determine the directionality from the fact of correlation, nor can you rule out that both Alzheimer's and weight loss might have the same cause, external to both. Most likely the weight loss is caused by the same deterioration of neurons as the later memory symptoms, except it occurs in perhaps the hypothalamus, the area of the brain that regulates weight. Thus it is more likely that Alzheimer's may cause weight loss, not vice versa, as you state in your discussion.

Use of causal language with correlational data shows poor understanding of science and/or lack of care in thinking or writing.

Randall Parker said at October 1, 2006 10:42 AM:

Nancy,

You say:

Thus it is more likely that Alzheimer's may cause weight loss, not vice versa, as you state in your discussion.

Yes, I agree that Alzheimer's probably causes weight loss. I think I stated that pretty clearly:

As reported above, even Alzheimer's causes weight loss before diagnosis.

You appear to think you are disagreeing with me. What did I say that makes you think you are taking a contrary position?

The brain damage caused by Alzheimer's could cut appetite by killing neurons that cause people to want to eat. If that the mechanism you mean to suggest then, yes, I agree with that as well.

Kurt said at October 1, 2006 3:24 PM:

I have noticed that the debate over the health effects of obesity has actually become polarized along the political spectrum, with the Right fervently denying that obesity has any ill health effects, what so ever. Why the left-right divide needs to concern itself with this political issue (unless its about public spending) is completely incomprehensible to me. Especially the response from the right.

The right seems to be hung up on people smoking a few joints from time to time, but think its perfectly OK to eat like pigs and (even in one case on townhall.com) to smoke (tobacco, not marijuana) like chimneys in public. I see no logical explanation for this. Perhaps you can provide one.

Randall Parker said at October 1, 2006 3:40 PM:

Kurt,

Some people on the Right fear (with justification) people on the Left using the harmful effects of some diets as a pretext to justify regulation of how we eat in considerable detail. So these people tend to dismiss the harmful effects of obesity in order to remove the justification for expansion of government regulatory powers.

There are plenty of people on both sides of the political divide with lots of motives for denying various findings of science about human nature and human behavior. Witness Leftists who deny that natural selection did much to make men and women different or the races different. Or the Christian fundamentalists who deny that natural selection produced the species. Science threatens both ideologies and religions.

Patrick said at October 1, 2006 8:11 PM:

Another confounding factor for the "similar risk of death in the overweight and regular weight" issue is the old one that so many studies use Body Mass Index as a proxy for overweight.

Anyone who looks at BMI knows perfectly well that BMI is a stupid measure. It does not distinguish between lean body mass (muscle and bone) and fat. While FAT may well increase the risk of death, lean body mass will decrease it. So if you lump the two groups (fit and muscular with the fat all being "overweight") then the two effects will cancel out.

Remember that I'm not talking about body builders here, I'm talking about the 75 year old ladies, one of whom is frail and 45 kg, the other a solid 65 kg who does daily walks and gardening. Which one will survive a fall or a bad flu better?

BMI is such a misleading measure that you could construct a conspiracy theory about why it is used so much.

John Thacker said at October 2, 2006 7:58 AM:

I have noticed that the debate over the health effects of obesity has actually become polarized along the political spectrum, with the Right fervently denying that obesity has any ill health effects, what so ever.

Well, Ampersand, who posts over at Amptoons, is hardly on the Right. I think it's difficult to characterize the "fat acceptance" people as on the Right. Opposing or fearing government regulation or lawsuits against people who sell fattening foods tends to be on the Right.

Sheila said at October 2, 2006 12:00 PM:

I wonder if the pre-Alzheimers weight loss has any connection to the glucose metabolism disfunction found in Alzhemers that was mentioned in your post last week that said "Alzheimer's looks to be a type of diabetes that is specific to the brain."

bbartlog said at October 2, 2006 12:18 PM:

I have a bit of a problem with trying to 'correct' the data this way. If you factor out diseases which are associated with prior weight loss to try and obtain the result you want, why not factor out diseases associated with prior weight gain? I am thinking of diabetes here, for example. I realize that you think that in the former case the weight loss is an effect, not a cause, while in the latter case you presume the weight gain is causative on some level, but this is an assumption on your part.

Maria said at December 30, 2006 10:25 PM:

What causes weight loss when someone is sick with a disease? Usually the weight loss is the outward sign something is wrong? What makes the body lose the weight?

Margaret Lenahan said at June 19, 2008 1:41 AM:

I am concerned that my husband is losing weight to fast, I know it bothers him too but he wont go to visit the doctor. I am talking pounds over a couple weeks, he eats well the only thing not enough fruit for my liking. He is down to eight pounds eight. He last weighed himself a couple of weeks ago and was nine stone something, I have not been to concerned and not taking much notice of what he has been telling me until now.


Mrs M Lenahan

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