People have circadian rhythms anticipating the day. They have monthly and seasonal rhythms regulating reproduction and metabolism. They have within-a-day rhythms, as in sleep cycles, hunger waves, and ultradian pulses of hormones from the brain to organs and back again. All of these rhythms happen across the entire body, and they all impact each other one way or another. To paraphrase John Donne, no organ is an island. This observation leads to two key predictions:
1) Changes in one organ should register in other organs. If A has an impact on B, and A changes, B should change too (proportioned by how big A's impact is).
2) Human bodies, left to themselves, should function like coupled-oscillator networks, and the various systems should form stable relationships in time.
Point 1 implies that if we knew all the As and all their impacts on all the Bs inside us, then we could use any A to extract information about any B. Maybe we can build a map of these nodes (the As and Bs). If so, then we should be able to find the most efficient sources of information from the network. In concrete terms, that means maybe we don't need to take blood work to measure a hormone if we know the impact that hormone has on changing your skin temperature.
This is why I am so excited by wearable sensors. If people could know about their hormonal health (e.g. is my water disrupting my endocrine system?), or their metabolic state (e.g. when is a good time to eat or dose insulin?) from a wearable, then they could keep an eye on it continuously. We'd know more for much less, about many more at once. Public health at the resolution of individuals.
Point 2 implies that coordination is the goal, and so loss of coordination is likely damaging. This fits well with our knowledge that shift work and jet lag are risk factors for health conditions. We can test this prediction by measuring multiple systems per person simultaneously, and assessing the ability to, for example, predict illness onset by loss of coordination.
This image is taken from a review where we outline the role of temperature monitoring in an effort to make use of this coupled-oscillator theory for detecting ideal meal time for an individual. The network graph at left cartoons how different hormones oscillate and act as nodes; their phase of oscillation may be tighter or looser, and change may be equal or unequal in both directions (illustrated by the length and width of the arrows). The blue, phase-locked nodes become disrupted by a poorly times meal, and that disruption propagates through the network, like knots in a net coming along when a knot near them gets pulled on. There is much work to do mapping the dynamic connections (edges) between all the nodes in our bodies, and much work to understand what level of coordination is too rigid, what too loose, and what information can be extracted from which nodes.