A BBC report of a new study by sleep researchers suggests that night shift workers have higher risk of various health problems than do we daytime doodlers; heart attacks, cancers and type 2 diabetes. This is because the expression patterns of many genes are based on the day-night cycle, and the 'chrono-chaos' of night work upsets lots of body functions, the story says.
The study, published in the Proceedings of the National Academy of Sciences, found that mistimed sleep caused gene expression to fall significantly. Genes affected included those having to do with circadian rhythms, or the maintenance of our sleep/wake cycles.
One can't be totally surprised, although one might expect that the graveyarders would get used to their diurnal cycle and do just fine. One has to wonder if there are other things about who chooses to do night work, or doesn't have options, so that nightshifting is a consequence rather than cause. In that case, nightshifting would be a confounder relative to the health implications rather than their cause.
The point here is rather just a brief one, that we and many others have repeatedly made. If these types of variables are not known or taken into account, or there isn't enough of this risk factor detectable in the study sample, then attributions of causation of what is measured will be inaccurate of misleading. This is one of the challenges of epidemiological research, including the search for reliable risk factors in the genome.
Then there is the question, related to an earlier point above, whether any genetic risk factors lead the bearer to look for nightwork and hence appear to be associated with some health result only indirectly. What about variants in the chrono-genes? Many such questions come to mind.
Inferential chaos?
Maybe, therefore, the chrono-chaos is a different form of informational and inferential disorder. A disorder of incorrectly done studies. As we know, many results of association studies, genetic or otherwise, are not confirmed by attempts to replicate them (and here we're not referring to the notorious failure to report negative results, which exacerbates the problem). We don't know if the 'fault' is in the study design, the claimed finding of the first study, other biases, or just bad statistical luck.
A piece in Monday's New York Times laments the high fraction of scientific results that are not replicable. This topic has not gone unnoticed; we've written about different reasons for nonreplicability over the years ourselves. The degree of
confidence in each report as it comes out is thus surprising, unless one
thinks in terms of careerism, a 24/7 news cycle and so on.
Indeed one of the problems with the study, is that it appears to be limited to what happens as the subjects' sleep schedule transitions from a normal pattern to that of a night-shift worker. Does not seem to look at what happens after weeks or months in the new schedule. Plus, from my own experience having worked a rotating shift at a chemical plant for about 16 months, one week days, one week evenings, and one week graveyard, the only way I could get my "normal" sleep during graveyards was to adhere to a strict bedtime schedule, something I was able to do because I was then single (though my social life did go down the drain). But my coworkers who had family and children could never count on having uninterrupted daytime sleep time, there being always some task or other that could only be done in daytime, not to mention those that had second jobs or side businesses to take care of. Daytime workers have the advantage that there is seldom anything that absolutely has to be done between, say, 9pm and 6 am.
ReplyDeleteWhen I was growing up, one of our neighbors had the night shift. I know that, kindly as they were to us, we kids and our outdoor playing noise were quite (unintentionally) disturbing to the poor guy, as he tried to get his Z's.
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