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Circadian Rhythms and Your Health Video and Transcript

Frank A.J. L. Scheer, PhD

  • Director, Medical Chronobiology Program, Brigham and Women’s Hospital  
  • Associate Professor of Medicine, Harvard Medical School

At the Medical Chronobiology Program, we study the role of the circadian system and its disruption on health and disease. Questions we investigate are, for example, why do people have an increased risk for heart attacks in the morning? Why is asthma severity worse at night, as compared to the day? And why is epilepsy more prevalent at certain times of day than the other? Other questions we are very interested in relate to why are shift workers at increased risk for obesity, diabetes, and cardiovascular disease? And then what applies to everybody, might it be of importance not just what we eat, but also when we eat for our health and our disease risk?

Understanding Circadian Rhythms

Circadian rhythms are rhythms that are generated by the body. Even if you place an individual in a constant environment and with constant behaviors, then there are many parameters in the body that still oscillate with a 24-hour rhythmicity.

So circadian rhythms are a product of the body clock. The biological clock is composed of a central clock in the brain called the suprachiasmatic nucleus in the hypothalamus, as well as virtually all the cells in our body that contain the same molecular machinery that can generate 24-hour rhythms.

Impact of Circadian Rhythms on Heart and Lung Function

There are ways in which the circadian system can affect our health. One is the normal functioning of the body clock when we are normally entrained to the light-dark cycle, and we're living in one time zone. In this scenario, the circadian system can regulate many physiological parameters, and in that way can make people more or less susceptible at particular times of day for adverse events. For example, in the morning hours, we have shown that the internal body clock regulates our blood clotting, and thereby may contribute to the observed increase in morning time for heart attacks, stroke, and sudden cardiac death.

Another example is nocturnal asthma. So for a long time, people have looked at behavioral factors to explain why people have worse asthma at night. So for example, is it because people are asleep? Is it because they are lying flat? We've been investigating whether it's actually the internal body clock that may drive pulmonary function, and thereby contribute to asthma being worse at night. And we have shown that, indeed, this is the case, such that pulmonary function, even if your environment and your behaviors aren't the same, will show a very large day-night pattern with worse pulmonary function at night.

Circadian Rhythms, Meal Timing and Glucose Control

In collaboration with Marta Garaulet from Murcia, Spain, we have found that the timing of food intake matters for people when they try to lose weight. So we found that when people eat their main meal earlier in the day that they lose about 25 percent more of their body weight during a 20 week long weight loss intervention. 

We have also found that meal timing is very important in glucose control. So we found that in the morning hours when you eat the same meal, that your glucose control is quite good but in the evening hours it’s not. This was known before, but we’ve now shown that the circadian system plays a dominating role in this morning evening difference.

We’ve just shown that in conditions where we desynchronize the internal system with the behavioral system that this causes a worsening of glucose tolerance. So the ability of blood sugar to be taken up from the bloodstream into the tissues is less effective.  The other thing we have shown is that misalignment between the behavioral rhythm and the internal circadian system causes an increase in blood pressure and also an increase in inflammatory markers. Together these could help explain why there is an increased risk for obesity, diabetes, cardiovascular disease in shift workers.

So where we’re heading next is we’re looking at the use of food timing as a countermeasure against the adverse, detrimental effect of misalignment. And this is especially targeted towards shift workers, because shift work will never go away.  But it’s also of relevance to basically all of us. So whether, if we switch the timing of food intake, we can actually have a novel therapeutic approach that can help in manipulating not just what we eat but also when we eat to improve our overall health.


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