This is the first study I know that directly tested this – the effects of rotating shifts on longevity – in humans, though some studies of night-shift nurses have shown large increases in breast cancers, stomach ulcers and heart diseases, and similar studies have been done in various rodents and fruitflies:
A study of 3,912-day workers and 4,623 shift workers of the Southeastern Central Railway in Nagpur showed the former lived 3.94 years longer than their counterparts on shift duties, said the study by Atanu Kumar Pati of The School of Life Sciences in Pt Ravishankar Shukla University, Raipur.
Shift work affects the circadian rhythm, the 24-hour cycle in the physiological processes of humans that leads to several sleep-related and social problems.
Circadian rhythms are important in determining the sleeping and feeding patterns of all animals, including humans. Brain wave activity, hormone production, cell regeneration and other biological activities are linked to this daily cycle.
Pati and his colleague K Venu Achari analysed a database of dates of death, retirement and death of each worker and published their findings in the latest issue of “current science”.
They also studied data on deaths due to all causes of 594 railway employees, including 282 day workers and 312 shift workers, over a span of 25 years. The cause of death was not documented in the database. An analysis of the data showed that day workers tend to live 3.94 years longer than counterparts working in shifts.
All day workers performed duty between 9 am and 6 pm with an hour-long lunch break from 1 pm and included those on office job and doing miscellaneous duties, the study said.
Those coming for shift duties worked in a rotating system consisting of a day shift (8 am to 4 pm), first night (4 pm to midnight) and second night (midnight to 8 am).
They worked in each shift continuously for six days and had a single day break before resumption of the next shift. The shift workers included running staff, gangmen and those doing miscellaneous jobs.
“The longevity of each worker was computed from the dates of birth, retirement and death,” Pati said. The researchers cited a number of animal studies that documented the life-shortening effects of weekly shifting of light-dark cycles.
It has been argued that these effects could be mediated through disruption of the circadian rhythm. Lighting schedule manipulation has also been reported to produce detrimental effects on the lifespan of insects.