Scientists have confirmed that disruption to the body clock by shift work or jetlag can have significant metabolic consequences.
Although epidemiologists have previously linked shift-work with an increased risk of developing certain conditions such as heart disease, stroke and breast cancer, it has always been difficult to disentangle the nature of the work and the environment from any knock-on metabolic consequences.
Now, writing in the current edition of PNAS, Harvard researcher Frank Scheer and his colleagues have confirmed the biochemical consequences of working the early shift on Radio National.
They placed ten volunteers in a sleep study environment where they were denied access to watches or clocks and, unknown to the them, the "days" were 28h hours long. This meant that over the ten day course of the study the participants' body clocks were progressively shifted until they were completely out of phase (equivalent to 12 hours jetlag), and then back into phase with their normal sleep-wake cycles.
Throughout the study period the team collected urine and blood samples and monitored the subjects' blood pressures, metabolic rate and sleep quality to see how this affected the physiology of the participants.
The results were dramatic: levels of the anti-appetite hormone leptin fell by 17%, with the most pronounced drop at the 12h out-of-phase point, the glucose levels of the subjects were 6% higher and their insulin levels 22% higher. The average blood pressure was 3% higher, and the "sleep efficiency" of the subjects was significantly lower - 67% versus 84% normally. Levels of the stress hormone cortisol, which should peak in the morning and fall during the day, were also reversed, leading to a surge in cortisol at the time when the subjects should have been going to sleep.
This shows that there are genuine and significant metabolic and biochemical effects associated with body clock disruption. The team point out that the identification of these changes will inform the more rational development of "countermeasures" to minimise the health impacts of shift-work.