Tuesday, March 9, 2010

Depression Obesity Link

A study just published in the March issue of Archives of General Psychiatry shows a bidirectional link between depression and obesity. The study found that obese people (as defined as a body mass index of 30 or more) have a 55% increase in developing depression and those with depression have a 58% increased risk of becoming obese. I want to discuss this briefly not only because of it's clinical value in knowing this link but also to talk about how studies like this one have significant problems that affect the results and lead to greater association or causation effects than is warranted by the data.

First, the study was retrospective. It was a chart review but this was not actually undertaken by the researchers. They analyzed 15 previous studies and compiled the data. This is a common practice and does yield valuable information but the fact that different studies are conducted quite differently needs to be taken into account. Some of the studies they reviewed just looked at whether or not obesity leads to depression or the other way around. Some looked bidirectionally. There needed to have the means of assessing how depression was evaluated published but there were some diagnosed by clinical interviews and some by self report.

The second problem is that the study did not take into account several factors which can effect the results. There was no assessment of the presence or absence of substance abuse. There was no assessment of medication effect. Many medications used to treat depression induce weight gain and without knowing that it may be that the association of depression and increasing obesity risk may be entirely due to medication effect.

I don't want to put down the study though. Meta analysis for public health problems such as obesity and depression are very valuable in establishing links but that is what they establish- links, not causation which even many researchers become confused about when they try to draw the meaning and significance of their studies.

So for now, we have established a strong link between depression and obesity but don't truly know that a bidirectional causation link has been established. Only a prospective study enrolling new subjects followed for a long period of time will give us that answer.

Thought for the day

" No evil is there similar to anger. No austerity to be compared to patience".

The Way of the Bodhisattva

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