This isn’t new news. For years, public health officials have forewarned us about the increased risks for car accidents, workplace accidents, and immediate declines in cardiovascular and neurological health following the springing forward. Nearly all of these studies attribute the connection between DST and changes in health risks to an hour of sleep loss because an opposite trend emerges when we fall back; there’s a decrease in these phenomena. This week, I decided to take advantage of the neuroscience institute’s experts in sleep and circadian rhythms and members of the cardiovascular institute in the same room for our quarterly journal club, and present a paper relevant to DST and changes in the incidence of myocardial infarctions. The findings of this paper published in 2013 are not novel but relevant. The study was a retrospective examination of hospital records from nearby hospitals in Michigan across six years (2006-2012). What is relevant about this study is that the landmark studies were from a Swedish database, making it difficult to extrapolate to US lifestyle because the Swedes are the healthiest industrialized nation in the world, while we are among the unhealthiest. The Swedes have a diet rich in antioxidants and anti-inflammatory factors and are much more active than their American counterparts who crave and live off of processed foods. That being said, isn’t the Swedish study a more convincing case for DST being a public health concern since their general population is already at a reduced risk compared to us? Yes, I believe so. But still, it is important to have a direct assessment of US health.
Here is a snapshot of the demographics of this study which included about 1,000 people. Most were in their early 70s. Nearly 50% had some cardiovascular event (major or minor) in the past, had been taking statins to control high blood pressure and cholesterol, and even other meds like aspirin. Surprisingly, very few had been diagnosed, about 3%, with sleep apnea or some type of sleep disorder.
When it came to looking at the incidence of heart attacks from falling back versus springing forward, the same trends as those in the Swedish study appeared. There was a reduction in risk on the Sunday of falling back and an increase in risk a few days after springing forward. Great. What the researchers failed to mention or statistically compare or to graph in an interpretative manner is that there is a higher incidence of heart attack at the start at the work week (Monday) in all cases;  in the groups of people going in for heart attacks around DST and even for the control groups who had a heart attack two weeks before or after DST. What is this about?
There were other seasonal affects as well such that springing ahead caused an increase in non-segmented heart attacks which result in partial damage to the cardiac muscle unlike segmented (full-blown) heart attacks. But the biggest issue here is that there is little mention of circadian contributions to these results. Yes, sleep is important, but an hour sleep gained or lost no matter how big the sleep debt is prior is trivial compared with the constant changes in social and environmental factors on a weekly basis. We are constantly flip-flopping back and forth from weekday to weekend schedules which result in different rise times, bed times, meal times, play times, etc that can wreak long-term havoc on physiological and behavioral systems since there is a constant need for re-entrainment. To me, social jet lag, less so environmental jet lag is the culprit in this study and the preceding landmark study, but this term along with any mention of “circadian†are omitted from both the introduction and discussion sections. It looks like physicians need some schooling on chronobiology….
Jiddou MR, Pica M, Boura J, Qu L, Franklin BA (2013). Incidence of myocardial infarction with shifts to and from daylight savings time. The American journal of cardiology, 111 (5), 631-5 PMID: 23228926