Clocking In

Are we expecting the night owls to be the early birds?



Subjecting shift workers to a schedule that is better suited to their internal body-clock (sleep-wake cycle) affects the general well-being of the workers (5). It results in better (quality and duration of) sleep (5). The important feature of this study, according to us, is its potential implications to human productivity.


Background for this work

People can be classified into chronotypes based on their internal body-clock that determines the time when they wake up and when they go to sleep (1).

The internal clock (circadian rhythm) is light entrained in humans, but is linked to a multitude of seemingly unrelated features of human life and well-being such as peak of physical activity (2-4).

There are known detrimental effects of going against the body-clock as seen in simulated night shift work (5). There are very few studies on whether aligning work shifts to a person’s internal clock (chronotype) can benefit them.


What did they do?

Workers in a factory (n= 114) were divided into 4 classes depending on their internal body-clock determined sleep-wake cycles as morning people (Early1 and Early2) and night people (Late1 and  Late2) with Early1 and Late2 representing  the extreme groups.

All the workers were subject to two kinds of schedules (shown in the cartoon above) –

Schedule 1 : Standard 2-2-2 schedule (2 days each of Morning, Evening and Night shifts) irrespective of their body clock.

Schedule 2: Chronotype Adjusted(schedule optimized to match the body clock), Early1: no night shift, Late 2: no morning shifts, Early 2:  more morning and fewer evening shifts and Late1: more evening and fewer morning shifts.

What did they find?

They measured the duration and quality of sleep on workdays and freedays, during the Standard Schedule 1, upon shift to Chronotype Adjusted Schedule 2 and towards the end of Chronotype Adjusted Schedule 2.

The extreme chronotypes (Early1 and Late2) benefited the most in term of work day duration of the sleep and the quality of the sleep due to alignment of the work schedule with their respective chronotypes (Schedule 2).

The difference between the sleep mid-point on workdays and on the freedays was used as another measure for changes in the quality of sleep. Surprisingly only Early 1 group showed significant improvement in this measure and not other extreme chronotype group, Late 2.

It is becoming increasingly rare for authors to discuss the limitations of their studies in their paper itself. We were therefore happy to note that Vetter et al., provide a thought provoking discussion which includes in detail the limitations of their study.

Pinch of salt:

Short intervention period (total study period of 6 months), mostly male participants, low number of participants at extreme chronotypes (Early1 and Late2 chronotype), lack of randomization.

The self- reported benefits  (measured as ‘workday well being’ and ‘satisfaction with time for social activities’) did not show a uniform effect in the different classes. Better measures, longer study period may be required to clarify or substantiate these findings.

Open Questions:

How will it impact the overall productivity of the organization if shifts were arranged based on chronotype?

Are there other physiological parameters that such studies could monitor, such as weight gain/loss, appetite, episodes of illness?