First, in order to answer this question, we must establish what is thought to be:
The main factors
Human-body temperatures can vary by nearly five percent in a single 24-hour period. A low temperature peak at approximately 4 – 5 a.m. and a high temperature peak near 5 p.m.
Can we change it?
Melatonin supplements are usually taken to regulate sleep patterns and cure insomnia. Evidence supports the idea that the circadian cycle can be influenced by taking this supplement. A low dose (0.5 mg) of melatonin between morning and mid-afternoon hours will delay the cycle, while it can be advanced by taking melatonin between mid-afternoon and bedtime.
It has also been proven in research that melatonin is a major influence on core temperature and circadian rhythm.
Bright light and darkness:
Bright light has the most direct influence on shifting our circadian rhythms. The intensity, duration and timing of the light are also important. Being exposed to bright light just before our lowest body temperature is reached (about 5:00 a.m.) delays our circadian cycle; being exposed to bright light after that time speeds up our circadian cycle. It has been concluded through clinical research that the use bright light and darkness can in fact influence the circadian rhythm, and help night workers / travellers adapt.
Some research shows that exercising one to three hours may induce significant circadian phase shifts. For example, early morning exercise performed before body temperature is at its lowest has consistently been associated with circadian phase delays; early evening exercise results in circadian rhythm advances. This is in fact supported in research, and the link seems to be in the fact that the exercise raises core body temperature at a key low point in the cycle.
Interestingly, it seems research suggests that the alteration to and from daylight savings time could also have an effect on our circadian cycle.
Yes, it seems we can influence our circadian rhythm, and there is some good research to support this belief. The basic fact will always be that there is an optimal and suboptimal time in the 24 hour day, and that it is governed by our internal body clock. Now you are armed with the facts, you can take steps to deal with the problem. This would apply to athletes / people who are night shift workers and those who regularly travel across time zones.
I aim to continue researching this topic by investigating personal experiences of dealing with the restrictions circadian rhythm can impose, and how people deal with that. Look out for it in future weeks.