While there’s a great deal of talk about circadian, or 24-hour, rhythms, new evidence suggests that 12-hour rhythms may actually have a greater impact on our health.

Diurnal animals, including humans, naturally sleep at night while remaining awake during the day. While this overall 24-hour rhythm of rest and activity is important, scientists are discovering an increasing number of ways that shorter 12-hour rhythms affect our lives. In fact, while we are awake, our body runs on a 12-hour cycle that is very important to our health. New research suggests that these 12-hour rhythms, also called ultradian rhythms, can impact our bodies in a variety of ways.

Understanding Your 12-Hour Rhythms

You have probably noticed that your body follows predictable patterns throughout your day. Maybe you get sleepy in the early afternoon or begin thinking about lunch around 12:00 p.m. sharp. These are not just habits, but products of a distinct internal 12-hour clock called the ultradian rhythm, which runs independently of your 24-hour circadian rhythm. Many physiological processes follow this 12-hour clock.

Chronobiology researchers have long noted that we appear to have these 12-hour rhythms, but only recently have they been able to measure them systematically. They measured the genetic activity of mice throughout their day and found that there was a predictable pattern of gene expression throughout the mice’s waking hours. Many of these genes expressed are ones tied to internal clocks; others were related to cortisol levels and various carefully timed factors. In total, more than 3,000 genes appear to be affected by our ultradian rhythm.

The Effects of Your Internal 12-Hour Clock

What processes does this daytime clock affect? Metabolism, in particular, appears to be regulated by this 12-hour rhythm, which makes sense as we are more active and need more energy when awake. Stress hormones such as cortisol also fluctuate predictably. Cortisol may be associated with stress, but it also has the effect of making us wakeful and helping us to think clearly. This may be why so many people become sleepy at the same time of day even when they get enough sleep at night.

The effects of these internal clocks appear to be huge and wide-ranging. Factors controlled by this 12-hour rhythm include how you react to stress, how you metabolize food and how clearly you make decisions. Your blood pressure, blood sugar levels and even how your body processes medications are all tied to the time of day. Understanding more about these factors could have huge effects on modern medicine. For example, we now know that people with kidney problems generally have worse kidney function at certain predictable times of the day. Medications and treatments in the future could be timed to prevent damage at these times. We also know that people have better cognitive skills and clearer thinking at certain times of the day. You may make better choices if you put off major decisions until these times.

Maintaining a Healthy 12-Hour Rhythm

It is clear that 12-hour rhythms affect our health more than we previously realized. New studies also suggest that these rhythms can be thrown off by working nights and other factors that throw our internal clocks off their timing. While more research will be needed, our 12-hour rhythms appear to work best when we awake and fall asleep at the same times of day, eat at the same times and otherwise try to maintain a predictable schedule. While modern life often demands that we keep erratic daily habits, this appears to negatively affect not just our ultradian rhythms, but also all of our internal clocks.

Your 12-hour rhythms help to support you throughout your day, priming you to be wakeful and alert at the times when these are most needed. In addition, they appear to support good kidney function, cardiovascular health and a variety of important factors. While it may be difficult to keep a steady schedule every day, this could have a huge impact on your health and productivity.