How Your Body Clock Affects Your Health

Circadian misalignment increased cardiovascular disease risk.


Humans naturally tend to want to be awake in the day and sleep at night. When the process must be reversed, it can be a problem.

Researchers from Brigham and Women's Hospital (BWH) found that when study participants abruptly shifted their sleep-wake patterns, heart disease risk increased.

Senior author Frank A.J.L. Scheer, PhD, noted in a press release, "We were able to determine, under highly controlled laboratory conditions, the independent impact of circadian misalignment on cardiovascular disease risk factors -blood pressure and inflammatory markers. Our findings provide evidence for circadian misalignment as an underlying mechanism to explain why shift work is a risk factor for elevated blood pressure, hypertension, inflammation and cardiovascular disease."

Dr. Scheer is a neuroscientist in the Division of Sleep and Circadian Disorders at BWH.

The human circadian rhythm -- commonly known as the body clock – usually calls for sleeping at night. People who perform shift work must reverse their wake-sleep hours.

The National Sleep Foundation notes that many biological processes are affected by the sleep-wake cycle. Exposure to light stimulates parts of the brain that control hormones and body temperature, among other functions.

Your brain secretes the hormone melatonin when it's dark, which helps you sleep.

When the sun comes up, the brain secretes cortisol, a stimulant that helps you stay alert.

Dr. Scheer and colleagues studied 14 healthy adults over two eight-day periods. The research was performed in the BHW sleep lab.

For the first eight days, study participants maintained their usual sleep-wake cycles.

For the second study period, the participants stayed on their normal schedule for three days. On the fourth day, they abruptly shifted to an 11 AM to 7 PM sleep cycle.

The researchers measured blood pressure and indications of inflammation, which indicate heart disease risk.

They found that circadian misalignment -- suddenly switching sleep patterns -- increased overall blood pressure and inflammatory markers. Both of these are indications of increased heart disease risk.

Dr. Scheer and team noted that more research is necessary to determine how other factors like eating and exercise might increase or decrease risk in cases of circadian misalignment.

The study was published in the February issue of the Proceedings of the National Academy of Sciences.

Funding for the study was provided by the National Institutes of Health and the National Aeronautics and Space Administration.

Information on conflict of interest was not available.