Caffeine and sleep disruption

Most of us have used caffeine. And most of us have heard that caffeine consumed close to bedtime can worsen sleep quality. I tell my patients to not have caffeine within 8 hours of desired bedtime. This was what I was taught in sleep fellowship. Apparently, there are few studies that have determined that people should stop consuming caffeine within so many hours of bedtime.

This study sought to determine how caffeine affects sleep quality when taken at bedtime and at 3 and 6 hours prior to bedtime. It's a small study, with only 12 healthy, younger volunteers. The volunteers did not have insomnia but did consume caffeine regularly. Sleep was measured by subjective report and by objective home monitoring. The results showed that the 400mg of caffeine negatively impacted sleep quality when taken at bedtime and at 3 and 6 hours prior to bedtime. Interestingly, caffeine affected both subjective and objective sleep quality when it was taken at bedtime and 3 hours before bedtime. However, the study participants did not report reduced sleep quality when caffeine was consumed 6 hours prior to bedtime. But objective home measurement showed that the caffeine taken 6 hours prior to bedtime did negatively impact sleep. This lack of perceived disruption in sleep quality may explain why some patients ignore recommendations to eliminate caffeine consumption close to bedtime.

Sleep Disturbance, Blue Light Transmission, and Yellow Lenses

Our biological clocks control important daily activities like sleeping. Sleep scientists have known for years that morning light exposure can regulate our biological clock to the 24 hour cycle. In particular, blue light appears to be the strongest clock stimulator. It tells our brains it's time to be awake by stimulating cells in the back of the eye, which then tell the sleep-wake centers deep in our brains.

As we age, the lenses in our eyes turn more yellow-brown in color - this color change can filter out blue light. This means that less blue light gets in to the back of the eye, so that the brain is not told as strongly when to be awake. This could result in sleep disturbances as older people's body clocks do not follow the typical 24 hour cycle. And, sleep quality has been shown to improve after cataract surgery, which is a replacement of the lens.

In the Sleep Journal, a study was done to examine the relationship between aging lenses in the eye and sleep disturbances. Researchers took 970 people ages 30 to 60 years old and asked them if they often suffer from insomnia or if they had bought prescription medications for sleeping disorders within the past year. A positive response to either inquiry was counted as a "sleep disturbance." The researchers also measured the amount of blue light transmitted through their lenses.

The results showed that 24.4% of the participants had a sleep disturbance. Also, the less blue light transmitted, the higher the risk of a sleep disturbance, even after correcting for age, sex, diabetes, smoking, and risk of ischemic heart disease. The study authors recommend that prescribing physicians reconsider sleep aids in patients that have undergone cataract surgery - they might not need them anymore.