The Transition to Daylight Savings Time and the Risk of Myocardial Infarction...

Dr. Isis has a mountain of data to pour through tonight, and yet there is just so much delicious, delicious science in her Google Reader. It's like all of the major journals have consipired against Dr. Isis to publish everything she would be interested in this week and prevent her from creating any of her own science.

Figure 1: The editors of Science, The New England Journal of Medicine, Circulation, the American Journal of Respiratory and Critical Care Medicine, Chest, and the Journal of Applied Physiology conspire to distract Dr. Isis

This evening I am nose deep in the middle of the new issue of The New England Journal of Medicine. The journal contains a very interesting synopsis on the presidential candidates' views on reproductive freedom. If you completely ignore the rest of my post (but, you won't because it's going to be totally hot), read the reproductive freedom article.

But, what has Dr. Isis all a twitter is actually a piece of correspondence from Swedish researchers Imre Janszky and Rickard Ljung entitled Shifts to and from Daylight Saving Time and Incidence of Myocardial Infarction. Janszky and Ljung present a very intriguing data set. It's just a shame their interesting data are confounded by their crappy interpretation.


Figure 2: Janszky and Ljung interpret their data.

The authors used the Swedish registry of acute myocardial infarction to compare the relative risk of MI during the year with the risk of MI in the week following the transition to daylight savings time. They found that the risk of MI was higher on the three weekdays immediately following the transition to daylight savings time in the spring and decreased on the first weekday following the transition back in the fall. The effect of the transition was larger in women and people younger than 65 (although they present no data, so Dr. Isis is not quite sure what this means).

Now, Dr. Isis avoided the authors' somewhat silly first sentence ("More than 1.5 billion men and women are exposed to the transitions involved in daylight saving time: turning clocks forward by an hour in the spring and backward by an hour in the autumn") but she could not avoid the sentence offering the authors' interpretation of the importance of their data:

The most plausible explanation for our findings is the adverse effect of sleep deprivation on cardiovascular health. According to experimental studies, this adverse effect includes the predominance of sympathetic activity and an increase in proinflammatory cytokine levels.

Clearly Dr. Isis missed the part of the paper where the authors presented their data indicating that the individuals in the database who experienced MI were more likely to be sleep deprived. And, she must have been too busy pouring herself a cocktail or staring at her hotness in the mirror to notice their data showing that sleep deprivation was highest in women and people under 65.

They continue:

Sleep-diary studies suggest that bedtimes and wake-up times are usually later on weekend days than on weekdays; the earlier wake-up times on the first workday of the week and the consequent minor sleep deprivation can be hypothesized to have an adverse cardiovascular effect in some people. This effect would be less pronounced with the transition out of daylight saving time, since it allows for additional sleep.

Now, this sounds more like the unabashed speculation it is clearly meant to be, but I am still disappointed at the attempt to string together logic in order to apply these data.

And, of course, my first thought is, what about all the other times we are sleep deprived by, you know, one hour. Is waking up in the middle of the night to feed Baby Isis potentially going to cause Dr. Isis to meet her maker early? In that case Baby Isis can freakin' starve. But, this is the New England Journal of Medicine and Dr. Isis appreciates the innate need that authors who publish here have to include some clincial applicability in their work. She only wishes they would have read this article first:

Hu, et. al. Endogenous circadian rhythm in an index of cardiac vulnerability independent of changes in behavior. PNAS 2004 101:18223-18227.

Or this one:

Hu, et. al. The circadian pacemaker generates similar circadian rhythms in the fractal structure of heart rate in humans and rats. Cardiovascular Research 2008 80::62-68

Or, above and beyond all other, this one:

Martino, et. al. Disturbed Diurnal Rhythm Alters Gene Expression and Exacerbates Cardiovascular Disease With Rescue by Resynchronization. Hypertension 2007 49:1104-1113.

Dr. Isis wonders how these jokesters were not familiar with Steven Sheas's work (the senior author on the above papers) and thinks that with a simple literature review the authors could have come up with something a little more elegant than "pro-inflammatory cytokines."


Figure 3: Proinflammatory cytokines, Dr. Isis's hot little ass. Original image is hosted here