Other work, collected by Circadian Information, a consultancy in Cambridge, Massachusetts, suggests people who work on shifts also suffer more ill health.

ECONOMIST: No more nine-to-five

In the circadian-gene mutants, however, the enzyme's activity stays steady after a dose of the drug, so tyramine levels remain low.

ECONOMIST: Flying high

Noticing the circadian pattern of Charles B's depression, Dr Wehr asked him to get through a night without sleeping, and then to increase his nightly sleep only gradually, so that for almost a week he was awake during those crucial early-morning hours.

ECONOMIST: People, like all living things, are four dimensional