There’s a reason you feel sleepy in the evening and naturally do not normally feel like sleeping during the day. That reason is the circadian rhythm, the body’s internal clock that controls various internal processes like body temperature, digestion, and blood pressure. Understanding the circadian rhythm may be the key to preventing various sleep-related diseases and conditions.

The circadian rhythm refers to the physical, mental, and behavioral changes humans experience over a 24-hour cycle. Several factors impact it, including changes in the environment, such as temperature and light. The occurrence of these changes out of their usual pattern may throw off your normal sleep-wake cycle.

Just as darkness sets in, your body begins producing melatonin, a hormone responsible for sleep. It slows down your body’s processes such as metabolism and other functions needed to maintain activity during the day. Melatonin secretion peaks at around 2 a.m. to 4 a.m., and then drops by sunrise, causing alertness.

You may have heard someone call himself or herself a “night owl” or a “morning person.” Neither is better than the other. They simply describe two distinctly varied circadian rhythms, and you can be a “night owl” or “a morning person” (also called “lark”) depending on your age, schedule, or social life. Your internal clock may shift from that of an owl when young to a morning person in old age.

Going to bed too early or much later than usual can interrupt this internal clock. Consuming alcohol, overeating, being exposed to bright light, or engaging in intense physical exercise too close to bedtime can also disrupt the circadian rhythm.

Ensuring your circadian rhythm is aligned may help promote sufficient sleep. However, when it’s off, significant sleep problems may ensue, like insomnia, or difficulty falling or staying asleep. Circadian health is critical, given the link between insomnia and mental health problems like anxiety and depression.

Poor sleeping patterns can cause sleep-related mood disorders. Sleep deprivation affects your emotional and mental health. It also hampers your alertness and focus during the day.

Studies of shift workers have established a close link between mood disorders and an out of sync circadian rhythm. Night-shift workers were found to be at a higher risk (40 percent) of developing depression than their daytime peers. What’s more, studies have identified out of sync circadian rhythm as a common problem among people with depression.

Circadian rhythm disturbances can also cause anxiety. When your nighttime activities impair your ability to fall asleep and stay asleep afterward, it may lead to anxiety. For example, jet lag studies show that travel-related sleep disruptions may lead to anxiety.

Seasonal affective disorder (depression that arrives at certain times of the year) demonstrates that factors beyond your control can affect your sleep-wake cycle. During the winter months, for instance, daylight is not as bright. This can disrupt your circadian rhythm, resulting in seasonal affective disorder.

The more out of sync your circadian rhythm is, the more severe your sleep problems are likely to be. To maintain a healthy circadian rhythm, go to bed and wake up at around the same time every day and avoid mentally and physically stimulating activities around the time your body should be slowing down (as bedtime approaches).

Sleeping disorders have far-reaching consequences. If you’re struggling to get a good night’s rest, talk to a doctor for an accurate diagnosis and the most appropriate treatment.