Heat and light can disrupt the natural body clock

Changes in light and darkness disrupt the human body clock causing ‘jet lag’, but EU-funded research on Drosophilia fruit flies has found that changes in ambient temperature can also disrupt the body’s natural circadian rhythms or body clock.

With daily temperature levels often closely linked to hours of sunlight, researchers found that heat and light misalignment produced dramatic changes in activity levels of fruit flies which are normally increasingly active throughout the 12 hours of daylight, peaking in the evening just before light and temperature levels drop.

As the effect of temperature on circadian rhythms has been less studied than the effect of light, the research led by University College London (UCL) and funded through the CLOCK MECHANICS project could help in optimising working conditions – such as regulating heating and air-conditioning to improve productivity, as well as improving people’s mental health.

‘Our findings indicate a higher biological relevance for temperature effects on daily behavioural rhythms than previously appreciated,’ the researchers say in a paper published in October in the journal Cell Reports.

Desynchronise heat and light

In a series of experiments, the natural cycle of 12 hours of light and warmth followed by 12 hours of darkness and cold was desynchronised so that the light cycle ran 2-10 hours behind the temperature cycle. A small time lag of less than four hours between the heat and light cycles had a relatively low effect on the body clock, and temperature cues dominated activity levels.

However, with a large time lag between the two, the body clock set itself according to the light, ignoring temperature – an indication that flies’ body clock can ‘orchestrate’ to some extent changes in a multisensory environment, rather than treating light and temperature completely separately.

The experiments also found that a ‘moderate’ time lag, of around six hours difference between heat and light cues caused confusion in the natural clock function, leading to major disruptions to fly behaviour – a result that had not been recorded before. Flies were only active during the six hours when it was both cold and light.

Robustness effects

With a misalignment of the different phases, the flies’ body clock resists some but adjusts to others indicating a robustness in certain circumstances. This could suggest behavioural habits may also play a role in how well flies adjust to disruption.

Signs of robustness could be important as links between human body clock disfunction and mental disorders have been made by other researchers, though the underlying cause and effect is still unclear. A better understanding of disruption to the body clock could also ‘enable novel approaches in the treatment and prevention of mental disorders,’ according to the researchers.

Though humans and other mammals, unlike insects, regulate temperature internally, if this research is replicated in mammals, it could have implications for more optimal regulation of the human work environment, including the way heating and air-conditioning might affect work and productivity.

The CLOCK MECHANICS project has received just under EUR 2 million in EU funding and will complete in August 2020.

For more information please see:
CORDIS project page