Your Circadian Rhythm Knows What Time of Day You’re Likely to Get Sick

As we enjoy these last few weeks of summer and move closer toward transitioning into fall, shifting our routines in ways that help support and boost our immune systems is always helpful to prepare for the arrival of flu season, which can begin as early as October according to the CDC. But sleep, diet, stress, environment, human contact, hygiene and colder weather aren’t the only variables that can affect our likelihood of getting sick.

According to a new study published in the journal Proceedings of the National Academy of Sciences, our circadian rhythms make us more or less susceptible to getting sick depending on what time of day it is that we’re exposed to viral infections. The circadian rhythm is the body’s biological clock that runs on a 24-hour cycle, influencing everything from sleepiness and appetite, to body temperature and blood pressure.

For the study, several healthy mice that were running on a 24-hour cycle with 12 hours of daylight and 12 hours of darkness were exposed to a herpes virus at different times of the day. The researchers measured the virus replication in the mice’s cells and discovered that replication was 10 times greater in the mice that had been exposed to the virus at sunrise compared to the mice that were exposed to it about 10 hours later in the evening.

The same experiment was conducted on mice that didn’t have a particular gene that helped regulate their circadian rhythm, and this time, researchers found no variation in virus replication dependent on the time of day that the mice were exposed to it. Virus replication was high right across the board, regardless of what time exposure occurred.

Since the study was conducted on mice, it’s not clear if the exact same effects would occur in humans, but previous research has shown similar findings. A growing body of evidence shows that the circadian rhythm can be altered either by lifestyle choices (like shift work) or by clock gene mutation (as shown in mice) in ways that disrupt responses from the immune system.

The researchers are now looking into how they can take advantage of potentially replicating the body’s naturally heightened immune response in the evenings. This may be done by developing medication that can be taken in the morning when the immune response is weaker.

Working With Our Circadian Rhythms

There are lots of lifestyle tweaks we can make to naturally ensure that our immune responses to potential pathogens are functioning well. Here are some ideas to consider:

Aim to get 7 to 9 hours of sleep per night. This is the most common sleep schedule that healthy adults are encouraged to implement into 24-hour schedules. Going to bed at the same time every night and waking up at the same time every morning is also ideal.

If you do shift work, find a sleep pattern that works for you. It’s an unfortunate truth that shift workers are more susceptible to viral infections and other health conditions, due to the havoc it can wreak on the circadian rhythm. Luckily, there are ways to deal with it. Consider implementing biphasic or polyphasic sleep patterns into your lifestyle if your job allows for it.

Get 20 to 45 minutes of daylight exposure first thing in the morning. Research has shown that exposure to light mostly before noon positively impacts the circadian rhythm. It’s also just a great way to feel more awake and alert!

Avoid exposure to bright light before going to bed. The same research mentioned above that exposure to blue light from devices like smartphones and TV screens can negatively impact our circadian rhythm when it’s too close to bedtime. We’re better off shutting everything down, dimming the lights and doing something relaxing at least 30 minutes to an hour before turning in.

Nobody has a perfect 24-hour routine that stays the same every day for their entire lives, but the point isn’t about being perfect. Our bodies are smart, and as long as we’re making an effort to stick with a routine that supports our circadian rhythm most of the time, with an occasional late night here or there, that’s what really matters.

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Photo Credit: Thinkstock


Sarah Hill
Sarah Hill1 years ago

Changing the time every 6 months can't help!

Stephanie B.
Stephanie B2 years ago


Jeanne Rogers
Jeanne R2 years ago

Thank you for sharing.

Marie W.
Marie W2 years ago


Quanta Kiran
Quanta Kiran2 years ago


Jacklyn Walker
.2 years ago

Sleep is something I've always found easy - If I'm sick I just naturally sleep 2 or 3 hours more per night- some types of antibiotics cause me to sleep 15-20 hours at nights - I've never really medically questioned it and have always consider that my body just needs extra shut down time and figure I'd rather be asleep than be awake feeling unwell - sulpha based drugs and food (like lotsa garlic or red wine) also makes me sleep alot - 7-8 hours is now a normal night - in my 20s I used to quite often go a day ot two either without sleep or very little - then it was like I'd still average 7 hours but in bigger chunks - ah the bodies resilience of youth - smiles

Siyus Copetallus
Siyus Copetallus2 years ago

Thank you for sharing.

Marc P.
Marc P2 years ago

Thank you for sharing!

Katie K.
Katie K2 years ago

I'm 100% with heather g. on her comment...."why mice need to be used for testing rhythms of humans" Contact with other humans is how we become ill so lay low, keeps hands off face and wash those hands with need for anti-bacterials

M Quann
M Q2 years ago

Thank you.