Monday, July 19, 2010

Not everything's caused by obesity: Brain and memory function edition


Good lord.

I know people like to blame obesity for everything. Every disease, every problem - everything.

You know what I'm blaming on it today? Authors' and peer reviewers' attitudes about their studies and results.

Last Tuesday I was asked by CTV to read a study that was pending publication in the Journal of the American Geriatrics Society so that I could comment on it for the national news. The study looked at 8,745 women between the ages of 65-79 free of dementia and evaluated their weight and waist to hip ratios in relation to their scores on the 3MSE, a modified mini-mental state examination validated to give an overview of cognitive function.

So I read the study.

Want to know what I found out?

That after controlling for age and education the test scores of folks whose BMI's were <25 were 95.2 while those whose BMIs were >40 were 94.1. I also discovered that the authors failed to provide the p value (the number whereby you'd see what the likelihood simple chance would lead to the result) for that comparison but they did provide a p value for the larger difference when age and education weren't controlled for and guess what, that p value, the one that looked at an even larger variance in test scores, wasn't even close to significant (at 0.10 there was a 10% likelihood the result occurred solely due to chance).

Another odd result? Women with abdominal weight distributions (apples) scored better than those with truncal distributions (pears) suggesting that unlike pretty much everything else weight related, abdominal obesity was protective against this supposed negative impact on cognition.

So basically in a best case scenario the authors could conclude that obesity may lead people to score a single percentage point lower on a test of global cognition but they'll point out at least that the difference in scores could easily have occurred due to chance. Worst case? They'll make it sound important so that they could get published.

My take? I took it to read that obesity doesn't lead to any statistically significant differences in a test of global cognition and that consequently it would seem that obesity and cognition aren't too tightly linked - a result that perhaps is bolstered by the fact that abdominal obesity appeared to be beneficial (though I should note, it may simply be due to the fact the researchers didn't measure waist circumference properly as rather than use a consistent bony landmark they used the floating umbilicus).

So what did the authors conclude?

"Higher BMI was associated with poorer cognitive function in women with smaller WHR....Further research is needed to clarify the mechanism for this interaction".
What I wrote back to CTV was the following,
"It would have to be an unbelievably slow news day for this to make the rotation."
And yet it was all over the news.

Sigh.

The media? I can forgive them, they're just trying to sell stories.

The authors? I can almost forgive them too as certainly negative publication bias might have precluded this piece and it's a publish or perish world.

The peer reviewers? I got nothin'.

Kerwin, D., Zhang, Y., Kotchen, J., Espeland, M., Van Horn, L., McTigue, K., Robinson, J., Powell, L., Kooperberg, C., Coker, L., & Hoffmann, R. (2010). The Cross-Sectional Relationship Between Body Mass Index, Waist-Hip Ratio, and Cognitive Performance in Postmenopausal Women Enrolled in the Women's Health Initiative Journal of the American Geriatrics Society DOI: 10.1111/j.1532-5415.2010.02969.x

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5 comments:

  1. Anonymous9:50 am

    Hi Yoni,
    Thanks for your summary on this ridiculous article. I will use it in my class for our epi/biostatistics students to critique!

    NGM

    ReplyDelete
  2. It says this was a study from a sample taken from the Women's Health Initiative study (a very major study, much in the news). Not being an expert, I just read on the study's website for the lay-public that it wasn't focused on cognition. Was this a follow up study?

    The study says a kind of cognitive test was given to subjects. Do you know what sort of memory or intelligence tests were given to members in the WHI at its initiation (or was this done at all)?

    Do you think the researchers are getting "play" by piggy-backing on the WHI's well-recognized name, and that this is why the press is paying it so much attention?

    ReplyDelete
  3. Hi crf,

    According to the psychologist who works with me at our offices the WHI actually administered some sophisticated neuropsychiatric tests.

    She was surprised that they bothered talking about the 3MSE as she says it can't be used the way the authors in this paper have done.

    I think the press are paying attention because the story, "obesity causes memory loss/alzheimer's etc in women" sells papers.

    ReplyDelete
  4. The fundamental shortcoming of this study is the manner in which cognition was assessed. In this case, a brief screening measure(1) designed for use in an elderly population to detect Alzheimer's disease was utilized. As such, this brief measure assesses orientation (e.g. do you know the date and where you are), memory, and language function; as these aspects of cognition are commonly compromised in Alzheimer's disease. However, this measure does not fully capture the changes in cognition found in obese individuals.

    In studies where a more thorough neuropsychological assessment has been carried out (2,3,4,5,6), findings suggest that functions subsumed by the frontal lobes of our brains, known as "executive functions" (e.g. processing speed, inhibition, decision making, planning, problem solving, mental flexibility, abstract thinking, shifting attention) are associated with obesity/BMI. These changes in executive functioning remain significant in a sample of obese individuals(4) even when controlling for common co-morbid medical conditions (e.g. hypertension, type II diabetes, and obstructive sleep apnea) that have a demonstrated association with deficits across cognitive domains (7,8,9,10).

    Brain imaging studies have begun to illustrate the role of the frontal lobes in obese individuals. A functional MRI study demonstrated that food reward processing may contribute to “pathological eating behaviour” (11). With regard to changes in brain structure in obesity, MRI findings demonstrated negative correlations between BMI and gray matter volume in the frontal lobes (12, 13), and has shown neuronal and myelin abnormalities in the frontal lobes (14).

    Unfortunately, the brief screening tool used in this study is not sufficiently sensitive to detect the executive dysfunction demonstrated in other studies. As such, any conclusions reached surrounding cognition are likely to be spurious, as a large portion of the expected cognitive changes demonstrated by previous research would not be detected by the measure utilized in this study.

    1.3MS: Teng & Chui, 1987
    2.Brogan , Hevey , & Pignatti, 2010
    3.Sabia, Kivimaki, Shipley, Marmot & Singh-Manoux, 2009
    4.Boeka & Loekken, 2008
    5.Gunstad, Paul, Cohen, Tate, Spitznagel, & Gordon, 2007
    6.Davis, Levitan, Muglia, Bewell, & Kennedy, 2004
    7.Battersby et al., 1993
    8.Manshot et al., 2006
    9.Ostrosky-Solis, Mendoza & Ardila, 2001
    10.Salorio, White, Piccirillo, Duntley, & Uhles, 2002
    11.Siep, Roefs, Roebroeck, Havermans, Bonte & Jansen, 2009
    12.Taki, Kinomura, Sato, Inoue, Goto, Okada, Uchida, Kawashima, & Fukida, 2008
    13.Pannacciulli, Del Parigi, Chen et al., 2006
    14.Gazdzinski, Kornak, Weiner, Meyeroff, & Nat, 2008

    ReplyDelete
  5. Anonymous3:40 pm

    This is a total chicken and the egg situation, but although the authors of the study are suggesting that cognitive deficiencies are a product of obesity, I think that it's more likely that any discrepancy in executive function compared to non-overweight subjects are because of biopsychosocial factors that led the people to already be that way, with obesity being a product of their inability to initiate and execute goals like losing weight. Either way, the the results are going to be linking "stupid" people with obesity, which is going to be offensive and controversial regardless. http://www.dietblogtalk.com has an article about a study that found that biopsychosocial factors led to several distinct personality types, some of which have a higher tendency to gain weight. i think if the science community actually communicated better and wasn't so compartmentalized we wouldn't see "results" like these as often...

    ReplyDelete