In Summary
  • When disrupted - as with jetlag - repeatedly over long periods, it can aggravate depression, bipolar disorder, cognitive function, and memory formation, research has shown.
  • Montaigne and his team deleted and replaced the corresponding genes in mice to study the impact on the transition between sleep to wakefulness, and vice versa.
  • But the discrepancy in outcomes between morning and afternoon operations might also be explained by variance in the biological clocks of the surgeons, he added.

The risk of serious heart problems after open heart surgery nearly doubles when the operation is performed in the morning rather than the afternoon, researchers said Friday.

Experiments and lab tests pointed to our biological clock as the primary cause of the startling difference in outcomes, they reported in the medical journal The Lancet.

"Our study found that post-surgery heart damage is more common among people who have heart surgery in the morning," said lead author David Montaigne, a cardiologist at the University of Lille.

"The time of day - that is, the biological clock or circadian rhythm - influences the patient's reaction to this kind of operation," he told AFP.

The circadian clock governs the body's day-night cycles, thus influencing sleep patterns, the release of hormones, and even body temperature.

When disrupted - as with jetlag - repeatedly over long periods, it can aggravate depression, bipolar disorder, cognitive function, and memory formation, research has shown.

Earlier this month, the Nobel Prize for medicine was awarded to three US scientists who pioneered our understanding of how the circadian clock ticks.

The new study unfolded in four steps.

To start, scientists examined medical records for nearly 600 people who had surgery to replace heart valves, half in the morning, half in the afternoon.

Fifty-four of 298 afternoon patients experienced heart attacks or other major cardiac events in the 500 days after the operation, compared to 28 out 298 of the morning patients.

Then, in a year-long clinical trial, 88 patients were randomly scheduled for morning or afternoon valve replacement surgery.

Not only did tissue from the afternoon group show less damage, it also regained the ability to contract more quickly in lab tests that mimicked the heart refilling with blood.

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