Our Body Clock Versus 24-Hour Time Clock

Written By:  Andrew Eide

Did you know that your body’s “clock” and the 24-hour time we live our lives to on a regular clock are different? To put it into the most basic terms time runs on a 24-hour schedule and our bodies run on a 24.5 hour schedule.

The body clock is your natural timing mechanism, and for most people, it runs a little longer than 24 hours. Basically it is a non-24-hour clock. For the sake of the discussion in this blog we will average it out to the body clock running on a 24.5 hour cycle. Some people run a little less, some run a little more, but the average is about a half hour longer than a normal 24-hour cycle we use on our clocks.

For some, it runs just a few minutes longer, and for others it runs much longer. The reason for this is not known.

For example, if your body clock is 24.5 hours, today you're running a half hour behind. Tomorrow you're an hour behind, and so on, until your natural rhythms have you sleeping during the day and awake at night. This continues and eventually your sleep-wake cycle briefly syncs up with the typical day-night cycle. Then it begins to move out of sync again. Some people experience a full circadian cycle as short as one and a half months. For others, it can be several months before their sleep-wake cycle is realigned with the 24-hour day.

The eye has two functions: to allow us to see images and to take in light. This light then signals the time of day to the brain. In people who are sighted, the non-24-hour master body clock is reset every day to 24 hours in the same way that hands on a clock can be reset. This ensures that the circadian rhythms synchronize to the typical day-night cycle.

For people who are totally blind, there are no such light cues. The body clock is left to run its natural course, with extra minutes adding up day-by-day until your circadian rhythms are essentially upside down from a typical 24-hour day.

Circadian rhythms are your body's tide. They control its natural ebb and flow. They keep its daily activity in sync with the 24-hour day, controlling the release of the hormones, melatonin, cortisol, etc. When you get sleepy during the day it's because melatonin is released preparing your body for sleep. When you're unable to sleep it's because cortisol has been released telling your body when to wake and when to eat among other things.

Melatonin, the hormone that controls sleep, is usually released in the evening. But in someone with Non-24 it could be released in the middle of the afternoon if his or her cycle at that point is opposite the typical day. Cortisol, the hormone that controls your metabolism, cardiovascular function, immune system, and appetite, is usually released in the morning. However in someone with Non-24 it might be released in the evening, disrupting the body's natural progress toward sleep.

This is how having circadian rhythms that are out of sync with the 24-hour day can impact the natural ebb and flow of the body.