Have you ever opened your refrigerator at night only to find your leftover lunch smell highly appetizing, although it wasn’t particularly delicious when you ate it in the afternoon? If it left you wondering whether the time of day has anything to do with your sense of smell, you might just have hit the nail on the head.
The circadian rhythm is a biological cycle that recurs at approximately 24-hour intervals. This rhythm explains why you sleep at night, wake up in the morning, and even why you have fixed mealtimes.1 So how does it have a role to play in your sense of smell? Let’s explore.
What Is The Olfactory Biological Clock?
The circadian rhythm is produced by your biological clock called the suprachiasmatic nucleus (SCN), located at the base of your brain. Interestingly, the circadian rhythm responsible for the variation in your sense of smell isn’t produced by the SCN but by your olfactory biological clock. This clock is located in the front of your brain, directly behind your nose.
Hence, it’s safe to say that both clocks are independent of each other. In other words, the variation in odor detection– even though it peaks at night – isn’t the result of your other daily patterns like waking up, eating, or going to sleep. The olfactory biological clock can go on even if the functioning of your SCN is compromised.2 3
How Does The Olfactory Biological Clock Work?
Now that we know your sense of smell varies based on the circadian rhythm, let’s find out how this works. To understand the mechanism, it’s important to note that your sensitivity to the cues of smell is dependant on a set of enzymes called GPRKs (G-protein receptor kinases).
The levels of GPRKs, in turn, are controlled by your olfactory biological clock. One study suggests that a spike in your olfactory biological clock increases your GPRK enzymes levels, which in turn, affect your sense of smell.4
When Is Your Sense Of Smell Most Powerful?
A study that aimed to find out whether adolescents’ senses of taste and smell influence obesity provided some interesting insights. The circadian rhythm of a group of 37 participants aged between 12 and 15 was analyzed. Their pattern of living was controlled so that it was drastically different from the one they were used to. The participants were awake for 17.5 h and asleep for 10.5 hours for a period of 9 days.
Every few hours, the teenagers took a scent test and sniffed a rose-odored chemical. The results revealed that the sensitivity to smell vastly differed from one person to another. However, on an average, the sense of smell peaked in the evening at about 9:08 PM and dropped between 2:22 AM and 10:10 AM. The result also indicated that food would seem more inviting during the evening, explaining the link between circadian rhythm, overeating, and obesity.5
Other studies have noted that the sensitivity to smell also depends on other factors like how long you’ve been awake and what other smells you’ve been exposed to during this time.
This discovery helps us understand how our sense of smell and appetite work, but that’s not all. It also emphasizes the importance of installing auditory fire alarms in our houses, as our sense of olfactory sense is turned down when we’re asleep.
|↑1||Circadian Rhythms. National Institute Of General Medical Sciences.|
|↑2||Do we have multiple biological clocks? Washington University in St. Louis.|
|↑3||Granados-Fuentes, Daniel, Alan Tseng, and Erik D. Herzog. “A circadian clock in the olfactory bulb controls olfactory responsivity.” Journal of Neuroscience 26, no. 47 (2006): 12219-12225.|
|↑4||Emery, Patrick, and Michael Francis. “Circadian rhythms: timing the sense of smell.” Current Biology 18, no. 13 (2008): R569-R571.|
|↑5||Herz, Rachel S., Eliza Van Reen, David H. Barker, Cassie J. Hilditch, Ashten L. Bartz, and Mary A. Carskadon. “The Influence of Circadian Timing on Olfactory Sensitivity.” Chemical senses 43, no. 1 (2017): 45-51.|