This essay has touched on a number of important areas in chronobiology research, but a few more should be mentioned. One intriguing area of research deals with the effect of biological rhythms on the efficacy of medication. W.J. M. Hrushesky, Department of Medicine and Laboratory of Medicine and Pathology, University of Minnesota Medical School, and Masonic Cancer Center, Mimeapdis, notes that in 31 patients with advanced ovarian cancer, the toxic side effects of anticancer drugs (which kill cancerous cells but can also kill or severely injure normal ones) were far more pronounced when the drugs were administered at certain times of the day.56 Administration time also affects the efficacy of drugs given to alleviate the symptoms of asthma57 and of indomethacin, an anti-inflammatory agent.58
Another important area of research involves biological rhythms and the effects of working late at night or on a continually shifting schedule, briefly mentioned earlier. In a letter to the editors of Nature, Simon Folkard, MRC Percepturd and Cognitive Performance Unit, University of Sussex, UK, and colleagues reported a circadian rhythm in the cycle of drowsiness and alertness that was independent of the sleep/wake cycle. 59This implies that there are certain times of day when workers will inherently tend to be more alert or more drowsy, depending upon their own internal rhythms. And indeed, Robin Dodge, Aerospace Medicine, Wright State University, Dayton, Ohio, notes that deftite rhythmic variations in alertness that are independent of lack of sleep have been observed in the crews of airliners.60
Chronobiologists are not yet certain what basic mechanisms underlie biological rhythms, nor is it understood how the clocks are set or whether they can be controlled, or reset, outside the narrow range that has been found in experiments so far. However, as we have seen, some intriguing hints concerning the answers to these areas have already appeared.
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