Experiments in three major types of biological organisms - human cells, algae, and fungi - found in each case that levels of magnesium in cells rise and fall in a daily cycle.
Scientists at the University of Edinburgh and the MRC Laboratory for Molecular Biology in UK found that this oscillation was critical to sustain the 24-hour clock in cells.
They found that it also had an enormous impact on metabolism in cells - how fast cells can convert nutrients into energy - throughout the course of a day.
"The new discovery could lead to a whole range of benefits spanning human health to agricultural productivity," O'Neill said.
The discovery in cells is expected to be linked to whole body clocks which influence daily cycles - or circadian rhythms - of sleeping and waking, hormone release, body temperature and other important bodily functions in people.
The finding may aid the development of chronotherapy - treatment scheduled according to time of day - in people, and the development of new crop varieties with increased yields or adjustable harvesting seasons.
Further tests showed that magnesium levels were linked to the cells' ability to burn energy. It was already known that magnesium is essential to help living things convert food into fuel, but scientists were surprised to discover that it also controls when this biological function takes place, and how efficiently.
"Internal clocks are fundamental to all living things. They influence many aspects of health and disease in our own bodies, but equally in crop plants and micro-organisms," said Gerben van Ooijen, from the University of Edinburgh.
The study was published in the journal Nature.
