Circadian rhythms are also referred to collectively as "the body clock," as they mark the way in which the human body processes time cues from the environment. These time cues include sunlight and seasons and temperature changes.
Our bodies are influenced strongly by these exterior cues, as they help to inform many internal processes in the human body as well, including sleep drive and digestion, among other things.
Hence, our bodies cycle in tandem with these rhythms, which occur following the same 24-hour pattern that represents one Earth day.
Think about it: The typical human being rises with the sun and goes to bed after the sun has set. When this very basic programming of the human body is diverted, many basic biological functions can be changed, thwarted or otherwise negatively impacted.
Research into sleep health and circadian rhythm dysfunction continues to show consistently how these kinds of disruptions to our rhythms can lead to cardiovascular problems, slower metabolism (leading to obesity), higher risk for cancer, and connections with mental health problems.
Some common circadian rhythm disorders can come as the result of lifestyle choices: jet lag occurs because of air travel across time zones, and those who work the graveyard shift can have a hard time achieving "recovery" sleep after working long overnight hours.
But some circadian rhythm problems are the result of internal disruptions.
Teenagers often has delayed sleep phase disorder, in which their drive to sleep launches later in the evening than their younger or older peers; these changes in "sleep phase" are brought about by chemical responses inside the bodies of teens that relate to their rapidly changing brain and body biology.
Keep in mind, delayed sleep phase problems are not just reserved for teenagers, but for anyone who can't fall asleep at a "typical" hour. Extreme night owls of all ages can find this problematic for keeping morning appointments or getting to work on time if it means they must cut short their nightly sleep due to delayed sleep phasing.
Elderly people often have advanced sleep phases, the opposite of what adolescents experience, which can explain why they are in bed by 6pm at night.
But again, people of any age can also suffer advanced sleep phasing, which can get in the way of work and family life as it often means these people cannot stay awake to participate in social time or work shifts that are scheduled in the early evening.
In addition, there are people whose rhythms do not match the 24-hour cycle... their days are typically longer than 24 hours, and this makes it difficult for them to live normal lives. They suffer because their sleep-wake cycles can become extremely desynchronized with the rest of the world.
Finally, the person who suffers from irregular sleep-wake phase suffers from the interruption of at least 3 sleeping periods during their waking day.
You can see how having intrusive periods of sleep or wakefulness at the wrong times of the day can make life hard for some. Employers and educators function on fairly regular working periods, so jobs can be hard to keep. Falling asleep at inappropriate times can be embarrassing, can lead to relationship stress, and can keep circadian rhythm disorder sufferers from leading full lives; they might even be dangerous.
Employers are starting to honor flex hours to respond to the needs of those who have dysfunctional circadian rhythms. Scheduling in hospitals and other workplaces where 24-hour shift work is the norm can help to give these employees a fair chance to recover from their overnight schedules so they can be better, safer workers. It's not unheard of for corporations to now have a nap room available to those who may need to catch a few midday winks.
Later school start times are one attempt to help teenagers to endure their naturally later sleep phases so they can be more productive and alert in class and so that they can avoid the sleep deprivation that delayed sleep phase can cause, which can lead to automobile accidents from drowsy driving and poor decision making in social situations.
Still, families can struggle when one or more members has a circadian rhythm disorder. Circadian dysfunction can lead to misunderstandings, unfounded assumptions about laziness, concerns that the sufferer has mental health problems, and mistakes that can make a home unsafe (kitchen fires, bad falls, and harm to unsupervised children are all potential risks).
To learn more about circadian rhythms, please visit the Circadian Sleep Disorders Network for in-depth information on each of these conditions and for resources for treating these conditions and raising awareness.