Tag: obesity

The paradox of the BMI paradox

~ BS

2016-10-19-17_52_02-physbe-talk-bs-pdf-adobe-reader

I had the honor to be invited to the PHYSBE research group in Gothenburg, Sweden. I got to talk about the paradox of the BMI paradox. In the announcement abstract I wrote:

“The paradox of the BMI paradox”
Many fields have their own so-called “paradox”, where a risk factor in certain
instances suddenly seems to be protective. A good example is the BMI paradox,
where high BMI in some studies seems to be protective of mortality. I will
argue that these paradoxes can be explained by a form of selection bias. But I
will also discuss that these paradoxes have provided researchers with much
more than just an erroneous conclusion on the causal link between BMI and
mortality.

I first address the problem of BMI as an exposure. Easy stuff. But then we come to index even bias, or collider stratification bias. and how selections do matter in a recurrence research paradox -like PFO & stroke- or a health status research like BMI- and can introduce confounding into the equation.

I see that the confounding might not be enough to explain all that is observed in observational research, so I continued looking for other reasons there are these strong feelings on these paradoxes. Do they exist, or don’t they?I found that the two sides tend to “talk in two worlds”. One side talks about causal research and asks what we can learn from the biological systems that might play a role, whereas others think with their clinical  POV and start to talk about RCTs and the need for weight control programs in patients. But there is huge difference in study design, RQ and interpretation of results between the studies that they cite and interpret. Perhaps part of the paradox can be explained by this misunderstanding.

But the cool thing about the paradox is that through complicated topics, new hypothesis , interesting findings and strong feelings about the existence of paradoxes, I think that the we can all agree: the field of obesity research has won in the end. and with winning i mean that the methods are now better described, better discussed and better applied. New hypothesis are being generated and confirmed or refuted. All in all, the field makes progress not despite, but because the paradox. A paradox that doesn’t even exist. How is that for a paradox?

All in all an interesting day, and i think i made some friends in Gothenburg. Perhaps we can do some cool science together!

Slides can be found here.

New article published: review on obesity and venous thrombosis

~ BS

Together with colleagues I worked on a review on the role of obesity as a risk factor for venous thrombosis. I’m second author on the article, which come online last week, and most work has been done by SKB from Norway, who is visiting our department for a full year.

The article is written from an epidemiological point of view and discusses several points that are worth mentioning here. First of all, obesity is an ill-defined concept: are we only talking BMI, or do also other measures of obesity need to be taken into account? Second, even when defined, the results are not always easy to interpret. In causal research there are a couple of things that need to be fulfilled before one can answer the question whether something is risk factor of disease. For example, BMI can be reduced by means of exercise   diet or disease, which all three have completely different effects on thrombosis risk. We discuss all these epidemiological problems, together with the existing body of evidence in the new article in seminars of thrombosis and hemostasis. These question are not only important for our understanding of thrombotic disease, but also to grasp the causal role of obesity in (cardiovascular) disease. This research question has in ast couple of years been put on the research agenda of the NEO study, on which perhaps more in the future.

The article, with the full title “Role of Obesity in the Etiology of Deep Vein Thrombosis and Pulmonary Embolism: Current Epidemiological Insights” can be found via PubMed, or via my personal Mendeley page.