What is circadian rhythm?
Your circadian rhythm is your internal timetable found in every cell and organ in your body, it guides how and when your body functions. It is a 24-hour master program that regulates what time of the day or night each of your genes (of which there are around 20,000) are expressed. This means it helps to regulate behaviour, physiology, metabolism and cell function. Our circadian rhythm is a mechanism that has been conserved throughout evolution to enable humans (and other organisms) to adapt to their environments, and synchronise their internal process to their external environments.
Research has now shown that a healthy circadian rhythm is a key component in peak performance and health optimisation, with dampening of the circadian rhythm known to be a driver of the aging process.
Many biological processes follow this circadian rhythm including, sleep, hormone production, NAD+ production and cellular energy production. Meaning that when our circadian rhythms are disrupted there are numerous systems impacted.
The central clock which regulates our circadian rhythm is found in the brain in a region called the suprachiasmatic nucleus (SCN). It is this central clock which communicates and synchronises with all the other clocks found in peripheral tissues to regulate cellular and organ functions.
Circadian rhythm, NAD+ and Aging
The circadian clock is known to regulate itself via a feedback loop. As shown in figure 1, the enzymes which it produces accumulate during the day and then at high levels they inhibit their own production. This process takes around 24 hours and then it begins again, as the clock is reset.
Cellular NAD+ levels naturally fluctuate throughout the day due to the circadian rhythm. Interestingly, studies now show that not only does NAD+ production follow the circadian rhythm, but also control the activity of the biological clock via its activation of sirtuins.
The two main proteins involved in this process are CLOCK and BMAL1. They bind to each other and then DNA to increase expression of its target genes, including the NAMPT gene. This is of importance as NAMPT is the key enzyme in NAD+ production. Levels of NAMPT directly influence how much NAD+ is recycled via the salvage pathway. Consequently, levels of sirtuin activation are also dependent on NAD+ availability.
Figure 1 – Regulation of the circadian clock
The proteins CLOCK and BMAL1 are the master regulators of the circadian rhythm. They bind to the DNA to promote transcription of target genes including NAMPT, Period (Per) and Cryptochrome (Cry). During the day as CRY and PER accumulate they act as a negative feedback loop, inhibiting the activity of CLOCK-BMAL1, and subsequently their own production. This cycle repeats approximately every 24 hours.
Tips to support your circadian rhythm
Our modern lifestyles are very out of sync with our circadian rhythm. Less time spent sleeping, continuous exposure to light from our devices, constant eating and shift work, all contribute to a dysfunctional circadian rhythm and this can impact your overall health. Satchin Panda, PhD, is a leading expert in the field of circadian rhythm research and these are his top tips for supporting your circadian rhythm to help you perform at your best.
- 8 hours in bed – Try to go to bed at the same time each night and get at least 7 hours of restorative sleep. During sleep our bodies produce hormones and chemicals to repair and rejuvenate our brain and body.
- Wait at least 1 hour after waking up to eat – after waking up our organs take around 1 hour to fully wake up. During this time our night-time hormones go down and our daytime hormones go up, and the body is not fully prepared to properly digest food.
- Time restricted eating (TRE) or intermittent fasting – try to eat breakfast at a consistent time every day and consume all your food in a limited window. Breakfast synchronizes all circadian rhythms in most of our organs. This pattern of eating in a consistent time and leaving between 12-16 hours of fasting is the best way to maintain a robust circadian rhythm.
- Get 30 mins of daylight – even on a cloudy day being outside for 30-60 mins is a brain booster and the best way to resynchronize our brain clock.
- Daily exercise in the afternoon – try to get 30 mins of exercise in the late afternoon or evening, when our muscles are most efficient and have the least risk of injuries to ligaments and joints.
- Wind down 2-3 hours before bed – avoid food for 2-3 hour before bed, this improves digestion, reduces acid reflux, and improves gut health. Dimming down light before bed increases production of night-time hormones such as melatonin to help you get restorative sleep.
Our circadian rhythm is essential to our overall health and performance, unfortunately it becomes weaker with age contributing to a variety of issues with sleep, hormones and metabolism. Research has now shown that lifestyle factors such as time restricted feeding, timing daylight exposure and regulated sleep habits can all contribute to maintaining a robust circadian clock with age.