PhotoperiodEffect.com

28. Why not call this the “melatonin hypothesis”?

The phrase “melatonin hypothesis” has been used by others to refer quite specifically to a proposed mechanism for the connection between breast cancer and shift work; the hypothesis being that exposure to extra light causes less melatonin to circulate, which melatonin might otherwise have destroyed or limited the cancer. But this is both a very narrow hypothesis, and may well turn out to be false. There is already at least one rat study contradicting this hypothesis. [11215676]

As is detailed in the reply to objection 20, above, a lot more than just melatonin is involved in our bodies response to night and day, so a broader “melatonin hypothesis” wouldn't suffice to explain all the damage from light, either. There are several likely pathways by which restricted darkness/extended periods of light (the Photoperiod Effect) may harm us, as detailed elsewhere, including metabolic dysfunction, induced immune system dysfunction and perhaps direct effects of aldosterone. Evidence can be adduced for each of these.

Moreover, the effect of shiftwork and light exposure detected in the case of breast cancer and shift work could yet turn out to be (partially or wholly) a marker for some other easily discovered variable or variables also caused by the photoperiod effect. Take for example obesity. It is known that obesity is a risk factor for some cancers, and I've hypothesized that modern obesity is largely caused by the Photoperiod Effect. If that's true, it wouldn't be entirely shocking if it were discovered that nurses on night shifts were as inclined to obesity as they are to breast cancer; and that the increased incidence of obesity amongst shift workers either partly or fully explained their subsequent marked tendency to breast cancer.