More than 70 countries around the world observe daylight saving time. In the United States, all states, except Arizona and Hawaii, turn the clocks one hour forward in the spring and one hour back in the fall. Many have questioned whether this change has health implications in the general population and, if it does, whether we should have health policies that take those health implications into consideration. One implication in particular has become a focal issue: heart attacks.
It’s important to look at the data we have on heart attacks and timing. A 2014 study analyzed data gathered from hospitals in Michigan between 2010 and 2013. It found that, in general, there were more heart attacks on Mondays compared to other days of the week. This bump in heart attacks was largely attributed to the added stress most people feel at the beginning of the workweek. Interestingly, there was an additional 25 percent increase in the incidence of heart attacks on the Monday after daylight saving time began, according to the study, which was published in the journal Open Heart.
The cumulative effect daylight saving time had on heart risk was complicated by the fact that there was a 21 percent decrease in the rate of heart attacks on the Tuesday after clocks were turned back one hour. This makes the overall heart attack incidence linked to daylight saving time neutral.
You might think that a one-hour change shouldn’t be much of a disruption. But consider that it’s the suddenness of the change that can lead to significant health consequences.
How it happens
The human body uses external cues or stimuli to maintain regulation of its internal clock. These cues are called zeitgebers, and one of the most important zeitgebers is sunlight. Certainly, daylight saving time would be disruptive to that process.
Manipulation of the sleep-wake cycle will affect the circadian cycle in the brain as well as hormone secretion and hormone levels — particularly levels of corticosteroids. These changes will also affect the function of the autonomic nervous system. The autonomic nervous system is mediated by adrenaline and noradrenaline, which influence blood pressure and heart function, among other processes.
An imbalance in the autonomic nervous system will cause a rise in pro-inflammatory substances called cytokines, which may precipitate cardiovascular events in susceptible individuals. This is of particular importance in people with preexisting heart disease, especially in those who already have plaques blocking circulation in the coronary arteries. This rise in inflammatory substances may precipitate platelets and other cells to aggregate and form clots, which have the potential to cause a complete blockage in one or more coronary arteries and a sudden heart attack.
Cardiovascular issues popped up in another study that looked at the effects of shift changes on workers and the resulting misalignment of their circadian cycle. The study, published in 2015 in the Proceedings of the National Academy of Sciences, showed shift changes at work caused increases in blood pressure and other inflammatory markers. This study bolsters the Open Heart study’s findings that pushing the clock for daylight saving time can impact heart attack risk.
Changes in daylight hours can have other, non-cardiac effects on the body. The earlier nightfall and shorter days of winter may cause problems for people who have a tendency toward depression. In fact, reduced exposure to sunlight during the winter can cause a condition called seasonal affective disorder (SAD). Not surprisingly, the standard treatment for SAD is light therapy.
Children may be affected, too
Another study published in 2014 observed the activities of children ages 5-16 during both seasonal and daylight saving time changes. The researchers showed that for every hour of daylight “lost,” there was a 5 percent decline in physical activity. This could have weight and sleep implications for children. Longer daylight periods were associated with a small increase in daily physical activity. Clearly, depending on the time of year, there are positive and negative health implications of different daylight exposure.
So, what can we learn from the current daylight saving time protocols, and how can we better manage these clock changes? Some strategies may include slowly adjusting to the time shift beforehand by going to sleep 15 minutes earlier every two to three days during the week before the daylight saving time change. Patients who do have heart disease might consider discussing medication changes (or additions) that will better control their blood pressure and heart rate in anticipation of the time change. This might include medications like beta blockers. Being proactive with a short-term change in medication protocol might help prevent this known increased risk for heart attacks.
It is, however, important to recognize that the new data on time shifts and heart troubles is not ironclad. The increased heart attack risk seems to occur among people who have other reasons (and risks) for cardiac events. It is unlikely that daylight saving time changes alone, as a singular risk factor, would cause cardiovascular events. It does, however, seem plausible that the time change would impact certain vulnerable individuals.
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