Research into the chronodisruption-cancer theory: the imperative for causal clarification and the danger of causal reductionism.

: A cascade of investigations into the validity of the chronodisruption-cancer theory (CD-CT), proposed 2008 in Neuroendocrinology Letters as a synthesis of abundant experimental and tantalizing - but still limited - epidemiological data, can be expected in coming years. In view of the possible public health relevance of the suggested links between chronodisruption, defined as the disruption of the temporal organization or order of biological rhythmicity over days and seasons, and the development of disease, including cancer, we provide practical aspects which should be considered for the planning, conduct and the very interpretation of such studies. The interrelated considerations address two facets: first, the critical necessity of causal clarification can be evinced appropriately by Poole's earlier contribution to the Journal. Researchers into the validity of the CD-CT should certainly consider Poole's 2002 illustration via causal graphs for shift work, light at night and breast cancer of the subtleties that can arise in the use of exposure surrogates of different kinds. Second, we emphasize the importance of considering the Zeitgeber multiplicity to avoid causal reductionism in epidemiologic - but also other - chronodisruption research.