Map of life expectancy at birth from Global Education Project.

Thursday, August 01, 2013

A couple of drive-by insights from the Global Burden of Disease

The GBD is a project of the World Health Organization, started in 1991. It's a massive effort to put together comparable morbidity and mortality statistics for all the nations of the world. The numbers are more reliable in some places than in others, and have all sorts of conceptual and systematic weaknesses, but they're the best we've got and they do tell us quite a lot that's interesting and important., review the changes in the U.S. and the world from 1990 to 2010. It's a complicated story, which they perhaps could have made more clear than they do in some ways. Read it if you're interested in understanding what's going on with the good ole human population, but I'll pick out a couple of noteworthy points.

They use a metric called Disability Adjusted Life Years, which is an attempt to measure loss of functionality and death in a common currency. You may or may not think that's morally correct, or even possible, but people who study public health think that something like it is necessary in order to compare the harm caused by various diseases or risk factors, and the value of competing investments in treatment or prevention. (I have covered this concept in the past.)  They make it a bit confusing by using the term DALY to mean its opposite, that is DALYs lost -- the sum of premature deaths and years spent living with disability. As far as I know this is not conventional, and they don't explain it. That seems to be an editorial oversight. But anyway . . .

Ranked by DALYs, the most costly disease in the U.S. is ischemic heart disease, which also happens to be the leading cause of death. The second leading cause of death, stroke, is number 7 on the DALY list. Since these are in considerable part manifestations of the same underlying disease, atherosclerosis, that's pretty impressive. Cancer of the respiratory tract is number 4 on the DALY list and number 3 on causes of death. That is mostly caused by smoking, which also contributes heavily to heart disease and stroke. So the major fact that we could have an enormous public health impact by getting tobacco out of our lives hasn't changed.

Something new is that dementia is now listed as the 4th leading cause of death, and its 12 on the DALY list. That's not exactly because we're having an epidemic of dementia, obviously, it's because we're living longer. Right now, there's exactly nothing we can do about it.

Globally, ischemic heart disease is now number 1 on the DALY list, and that's a measure of how deaths from infectious disease have fallen globally while life spans have increased, even in the poor countries. (Lower respiratory tract infections were number 1 in 1990, and heart disease was number 4.) This is true in spite of the HIV epidemic, and it's largely due to a decline in deaths of children from diarrhea. That's actually something of a global success story.

Compared to the rest of the world, we're much more likely to die from dementia -- because we live a long time and don't die from other stuff -- but also from lung cancer, because the tobacco epidemic started here. (Don't worry, the world is catching up.) So, obesity and physical activity are indeed major challenges, but tobacco is still with us. Now is not the time to stop fighting it.

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