This month, in celebration of the 100th anniversary of the American Physiological Society journal Physiological Reviews, we are highlighting recent research published in the journal. Interested in reading more in celebration of Physiological Reviews’ birthday? Read our spotlight on migraine, about bariatric surgery’s effect on hunger and about targeting the immune system to treat cancer.

It’s the middle of the night and you lie awake in bed looking at the clock, trying to count sheep or do whatever it takes to fall asleep. The inability to fall or stay asleep—even though you’re tired—can put a damper on your energy, mood and health.

Insomnia is the most common sleep disorder, one that roughly one-third of us experience at one time or another. A recent review published in Physiological Reviews explains that insomnia often goes along with other health conditions, including other sleep disorders such as sleep apnea. The review highlights what’s happening in the brain to make you not be able to sleep.

Sex

Women are more likely than men to have insomnia, in part due to the fluctuation of sex hormones. Puberty, pregnancy, certain phases of the menstrual cycle, and menopause may all aggravate insomnia symptoms. Studies have also found differences in structures in the brain involving sleep regulation and circadian rhythms between the sexes.

Genetics

Some people are born with it—the risk of developing insomnia, that is. Research suggests sleep difficulties run in the family. However, it can be hard to tell from studies alone if this is a true genetic trait shared by family members or if living in the same environment with similar habits contributes to the problem. Scientists are looking into this question by analyzing genes associated with sleep regulation.

Mental health

Stressful life events can lead to insomnia in some people. Those with bipolar disorder, depression, anxiety and post-traumatic stress disorder (PTSD) also have a higher risk. However, in the case of PTSD, it’s not clear which comes first: insomnia that leads to PTSD-like symptoms or PTSD that leads to sleep disturbances.

Brain structure

Imaging studies have found changes in the brain’s white matter (the area affecting learning and memory) in people with insomnia. Network connectivity—how your brain cells communicate with each other—also looks different in some people with insomnia. More research will help determine if these differences are because of insomnia or the cause of the problem.

If you have trouble sleeping, there are steps you can take to get better rest:

• Stay on a set sleep schedule as much as possible without taking daytime naps.
• Exercise regularly. Physical activity can improve sleep quality.
• Limit your consumption of caffeine, alcohol and nicotine.
• Keep your bedroom at a comfortable temperature.
• Put away your phone and other electronics an hour before bedtime.
• Ask your doctor about taking a sleep aid such as melatonin or over-the-counter medication.

It’s frustrating to not be able to sleep. However, ongoing efforts to learn more about what causes insomnia will help researchers discover how we can all rest easier in the future.

—Erica Roth