When the clocks are moved ahead for daylight saving time, the disrupted circadian rhythm could result in a heart attack, some researchers contend.
"Every cell in the body has a molecular clock that allows the cells and organs to anticipate the day's events," Martin Young, PhD, a professor and researcher at the University of Alabama at Birmingham, told 鶹ý.
"When there are time changes, such as shift work, traveling through time zones, or daylight saving time, it takes a while for these cells to reset their internal timing mechanism," he said.
For people who already have one or more risk factors for cardiovascular disease, the loss of an hour's sleep in the first few days after daylight saving time could just be the "additional risk factor that takes them over the edge," Young said.
Although there have been on this phenomenon, the most recent appeared this month.
Imre Janszky, MD, PhD, of the Karolinska Institute in Stockholm, and colleagues used a Swedish registry to compare the incidence of acute MI on the first seven days after daylight saving time went into effect with other time periods ().
They found an elevated incidence ratio of 1.039 (95% CI 1.003 to 1.075) for the first week after the "spring ahead" time change.
They found no statistically significant change in MI incidence following the autumn "fall back" clock shift.
Interestingly, preclinical studies suggest that animals whose internal clocks are genetically manipulated have an increased risk of developing heart disease, Young said.
In addition, he said, when the sleep-wake cycle in experimental models is disrupted, the response of the immune system to a challenge is altered.
Preclinical studies by Alec Davidson, PhD, of Morehouse School of Medicine in Atlanta, and colleagues found that mice that were subjected to jet lag or to shift work conditions died more often than controls. Researchers also found that the experimental mice had a weakened immune response (J Immunol 2010; 185: 5796-5805).
Brain wave scans revealed the mice subjected to shift work conditions did not lose sleep. Davidson and colleagues suggested that these mice were reacting to a heightened release of proinflammatory cytokines.
In contrast, the jet lagged mice exhibited changes in the expression of circadian clock genes. The researchers concluded that the adverse events in the jet lagged mice were caused by circadian disruption and not sleep loss or stress.
Davidson and his colleagues are currently determining what diseases appear in these mice, in order to relate them to humans.
Independent of the one-hour time change on daylight saving day, Monday morning is the time people are at greatest risk of having a heart attack than any other day of the week, Young said.
There are several hypotheses for this phenomenon, including the stress of going back to work. But Young said the daylight saving time research sheds new light on the problem.
During the week, people generally have a routine of going to sleep and waking at the same time. Weekend activities change the routine. The loss of sleep on weekends could account for the increased risk of MI when they go back to getting up early on Monday morning.
To help fend off the daylight saving time heart attack threat, Young suggests the following:
- Wake up 20 minutes earlier on the Saturday and Sunday of clock-change weekend. On Monday, do the same. Rather than shocking the system with an hour difference, it's merely one of 20 minutes.
- First thing on Saturday and Sunday get exposed to light.
- Don't skip breakfast, "which people tend to do on weekends."
- Be active on Saturday and Sunday -- exercise is a good way of resetting the internal clock.
One interesting bioclock phenomenon, Young noted, was seen in a study of vacationers in Hawaii: The timing of their heart attacks correlated mostly to morning in their home locale and not the local time in Hawaii.