*Geek Box: Different Clocks of Life

*Geek Box: Biological, Social, and Solar Clocks

Reading any circadian or chrononutrition research can mean seeing continued reference to “clocks”, and it can become confusing as to what is actually meant by terms like “biological timing”. So it can be helpful to clarify the different “clocks”, and how they interact. The most appropriate point of departure is the “solar clock”, as it is the cycle of light and darkness – day and night – around which the daily rotation of the Earth represents, and around which the internal rhythms in biological processes (known as “circadian rhythms”, meaning ‘around the day) of almost all organisms on Earth have developed.

“Biological clocks” therefore represent the internal timing of these rhythms that, ideally, is synchronised to the solar clock, i.e., consistent with the cycle of day and night, light and dark. Finally, we have “social clocks”, which is the timing of our social activities, and may also be referred to as “local clock time”, i.e., the time in a given part of the world. As Professor Till Roenneberg has highlighted, before the introduction of time zones and artificial light, the social clock was in synchrony with the solar clock: 12pm midday was when the sun reached its peak, and 12am midnight was 12hrs later halfway between sunset and sunrise. This timing of social activity with the solar clock, and before the introduction of artificial light, meant that biological clocks were consistent with both solar time and the timing of social activities.

However, in modern industrialised societies, local clock time remains constant, however the timing of social activities may be inconsistent with biological clocks, facilitated by artificial light, communications and travel across time zones, and little to no consistency with the solar clock – in industrialised societies people spend up to 88% of their time in enclosed buildings. Most of us just think of “time” as the time on our watch, or on our phone. But this is just a representation of the ‘local time’ in our part of the world. It may be that human health is influenced by the consistency between our internal biological clocks and the synchrony of those clocks with the solar clock, and our social clock timing.