With all of the good that our modern environment and lifestyle offer, the opportunities to live a life that is misaligned with our genetics and physiology are plentiful. It doesn't take much to recognize many factors that are novel to our current world in regards of our environmental exposures.
One insidious element that can negatively affect our bodies natural rhythms is artificial light. Now light can be friend or foe when speaking about our natural rhythms. Historically, we would begin to rise and be greeted by the bright light of the sun. This would in turn stimulate entrainment of our circadian rhythm supporting wakefulness, a sensitive metabolism, and energy production through the day, and conversely restfulness and the appropriate physiology for good sleep. However, in our modern environment we are exposed to artificial light at all times of the day and have seen a trend towards less and less exposure to natural light. 
With the sensitivity of the human organism to light it is no great surprise to see that exposure to artificial light late in the day can cause what is called, “Phase Shift Delay.” Phase Shift Delay is referring to the effects that bright light at night has on the secretion of melatonin. Light exposure in the evening can lead to a delay in the secretion of melatonin. Melatonin is a hormone that is responsible for sleep onset. Evening light exposure can delay the secretion of melatonin till after one is already asleep. Furthermore, the phase shift delay that happens pushes the whole hormonal process back in time. Melatonin is active in the body until after one wakes and cortisol, which is normally highest shortly after waking then trends down through the day, waits to peak until later in the day, contributing to heightened wakefulness later in the day and the evening. Modern technology is being seen to play a critical and deleterious role in the misalignment of our natural circadian rhythm. It has been well documented that the use of phones, computers, tablets, etc. can have major impacts on us and contribute greatly to a phase delay shift. 
Many other factors can contribute to circadian rhythm disruptions: long flights, shift work, meal timing, and stress.
In response to acute stress production of cortisol and other glucocorticoids is elevated, stimulates increased wakefulness, a higher mobilization of free fatty acids, and enhanced memory. When stress is chronic we start to see the inverse of these adaptive responses: cognitive impairment, immune suppression, and negative metabolic consequences. Therefore we can see that elevated stress levels, which have been increasing in the modern age, can contribute to circadian disruption and many of the other consequences that stem from it.
In addition to the master circadian clock, there are peripheral clocks in other tissues that take their cue from signals other than light. The Liver for instance finds itself on a strongly circadian rhythm that is stimulated from the initial ingestion of a calorically containing substance, food. We have seen that during our wake cycle our metabolism is most sensitive. When we choose to have late night meals and snacks it can be an additional factor for our circadian disruptions. Leading to accumulation of fat mass and disturbed sleep as the body is in need of processing the food when it would otherwise be resting and repairing. 
The consequences of, and contributors to, disruption of our wake/sleep cycles are many and varied. Luckily, we can do a lot to manage them through engagement and design of our diet and lifestyles. Look for part 2 & 3 for some suggestions for solutions.
Wright, K. P., McHill, A. W., Birks, B. R., Griffin, B. R., Rusterholz, T., & Chinoy, E. D. (2013). Entrainment of the Human Circadian Clock to the Natural Light-Dark Cycle. Current Biology : CB, 23(16), 1554–1558. https://doi.org/10.1016/j.cub.2013.06.039
Hatori, M., Gronfier, C., Van Gelder, R. N., Bernstein, P. S., Carreras, J., Panda, S., … Tsubota, K. (2017). Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies. NPJ Aging and Mechanisms of Disease, 3. https://doi.org/10.1038/s41514-017-0010-2
Figueiro, M. G., & Rea, M. S. (2010). The Effects of Red and Blue Lights on Circadian Variations in Cortisol, Alpha Amylase, and Melatonin. International Journal of Endocrinology, 2010, 1–9. https://doi.org/10.1155/2010/829351
Landgraf, D., McCarthy, M. J., & Welsh, D. K. (2014). Circadian Clock and Stress Interactions in the Molecular Biology of Psychiatric Disorders. Current Psychiatry Reports, 16(10). https://doi.org/10.1007/s11920-014-0483-7
Albrecht, U. (2012). Timing to Perfection: The Biology of Central and Peripheral Circadian Clocks. Neuron, 74(2), 246–260. https://doi.org/10.1016/j.neuron.2012.04.006