Your body’s clocks

I think most of us are aware of our circadian rhythms—our bodies’ sleep cycles. They’re controlled in the hypothalamus part of the brain. In the evenings, our brains release hormones that lower our body’s temperature and blood pressure and make us feel sleepy. In the morning, cortisol and other hormones restore our alertness, make us warmer, and increase our blood pressure. Now scientists know that every cell in your body contains a group of genes that function as a sort of mechanical watch, keeping time everywhere in our bodies.

These “clock genes” represent every physiological system: skin, liver, immune system, kidney, heart, lungs, muscles, and reproductive system. Disrupting our circadian system can have a significant negative impact. Your liver, for example, determines when to rev up your metabolism based on when you eat.  If you eat in the middle of the night, your liver—which your brain has instructed to rest—will process the midnight food less efficiently than it would have during the day. Among other effects, eating at night increases the risk of glucose intolerance because the kidneys and pancreas are also primed to rest at night. Similarly, being exposed to light when our body ought to be resting can have a negative impact, including impaired glucose and cardiovascular regulation. Some studies have shown that light during sleep—such as leaving the TV on—is a risk factor for obesity.

A bunch of scientists are trying to influence hospitals to change their ways. (As I’m sure you’re aware, hospitals are one of the worst environments for maintaining circadian health—both for staff as well as patients.) For example, research has shown that premature infants who receive 12 hours of light followed by 12 hours of darkness are discharged an average of two weeks earlier than those who are exposed to near constant darkness or near constant light. Scientists are also studying the best time to take drugs. For example, they found that taking low-dose aspirin in the evening is more effective than taking it in the morning.

 The timing of our clocks varies by individual, which in turn is affected by genetic predisposition, the sun, indoor lighting, behavior, and age. In general, circadian researchers suggest getting as much sunlight as you can during your day, especially upon waking, dimming the lights before sleep, making your bedroom dark, and eating most of your calories earlier in the day. Easy for me; not so easy for night-shift workers.

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