Recent research1 reveals that you have more than one biological clock in your body. As it turns out, virtually every organ in your body has its own clock or circadian rhythm, and in order to keep them all in sync, you need to keep a regular waking and sleeping schedule that is linked to the rising and setting of the sun.
When your sleep schedule is erratic, a cascade of effects can occur, raising your blood pressure, altering hunger hormones, and disrupting your blood sugar control, for example.
Chronic sleep disruptions also promote metabolic dysfunction that can result in weight gain and type 2 diabetes. It also increases C-reactive protein, an inflammatory marker associated with deadly heart attacks.
Basically, the various systems in your body are programmed to perform scheduled tasks at specific times during the 24 hour wake-sleep cycle, and when you consistently act against these clocks, your internal systems start to malfunction.
Shift workers who stay awake all night and sleep during the day are especially at risk.
For example, three years of intermittent night shift work can increase your risk for diabetes by 20 percent, and this risk continues to rise with time. Shift workers also have higher rates of obesity, and a four- to five-fold higher rate of cancer than the average population.
How Light and Darkness Influences Your Health
Ever since the advent of the light bulb, people have become increasingly “darkness deficient” at night, while simultaneously getting too little light during the day, courtesy of working indoors.
In terms of light intensity, outdoor light is far more intense than indoor light. Light intensity is measured in lux units, and on any given day, the outdoor lux units will be around 100,000 at noon. Indoors, the typical average is somewhere between 100 to 2,000 lux units—about two orders of magnitude less.
The brightness of the light matters, because your pineal gland produces melatonin roughly in approximation to the contrast of bright sun exposure in the day and complete darkness at night.
If you are in relative darkness all day long, it can't appreciate the difference and will not optimize your melatonin production, and that can have some rather significant ramifications for your health.
We now know that a whole host of physiological processes are directed by your endogenous circadian rhythm, which is calibrated to the rising and setting of the sun—provided you’re exposed to natural sunlight and darkness. As explained in the featured article:2
“The light – and the dark – are important signals for the cycle. This circadian rhythm has developed over three billion years as life evolved on Earth in the context of the sun’s day/night cycle. It is built deeply into our genetic makeup.
During the night, in the dark, body temperature drops, metabolism slows, and the hormone melatonin rises dramatically. When the sun comes up in the morning, melatonin has already started falling, and you wake up.
This natural physiological transition into and out of night is of ancient origin, and melatonin is crucial for the process to proceed as it should.
If you were to put someone in a dark cave with no time cues at all, the cycle will last about 24 hours, but not exactly. Without time cues like those from the sun, eventually that person would become out of sync with people outside.”
Aside from lowering body temperature, slowing metabolism, and raising melatonin, your body also undergoes a number of other changes when in the dark. For example, levels of the hunger hormone leptin rises, which decreases feelings of hunger.
Research3 has shown that when you’re exposed to light at night, even if it’s brief, your leptin level decreases, which makes you hungry in the middle of the night—a phenomenon that wouldn’t have been very convenient for our ancestral hunter-gatherers.
Gene expression is also affected by your endogenous circadian clock, as is cellular growth and repair, and hormone production. Exposing yourself to light at night leads to the disruption of all of these processes, setting the stage for diseases like obesity, diabetes, cancer, and depression.