Insomnia from menthol in toothpaste?

Genes and environment conspire in this cause of insomnia, but the environmental factors can be changed, to solve this issue.

Liver enzymes are responsible for metabolizing many substances, in order for the body to excrete them. In this case, a liver enzyme called CYP2A6 is at fault. CYP2A6 metabolizes nicotine and menthol (Miyazawa et al, 2011), among other things. As with many other genes there’s a variation, called polymorphism. Some mutations or deletions in this gene can make the enzyme totally inactive (López-Flores et al, 2017), if not just less active, unaffected or more active.

That brings us to the environmental factors. Menthol has an ability to keep the mind awake and active (Norrish and Dwyer, 2005). For people with functional CYP2A6 enzyme this effect disappears quickly, but for people with dysfunctional CYP2A6 enzyme the alertness lasts longer, so much that menthol toothpaste could prevent sleep for two+ hours. The effect causes what many with insomnia have experienced, being sleepy but unexpectedly the mind stays awake and very active. Further on, as is well known, laying awake and getting stressed can worsen the insomnia, prolonging the awake time and even causing unwanted wake ups.

Individuals who suffer from insomnia should assess if changing to a menthol free toothpaste make them fall asleep quickly. Another option could be to brush the teeth at least two hours before sleep, to have the menthol effect wane off before trying to sleep.

Research on the prevalence of this cause of insomnia would be welcome.

References:

López-Flores et al, 2017
Luis A. López-Flores et al. Distribution of polymorphic variants of CYP2A6 and their involvement in nicotine addiction. Excli J. 2017; 16:174-196.

Miyazawa et al, 2011
Miyazawa M. et al. Metabolism of (+)- and (-)-menthols by CYP2A6 in human liver microsomes. J Oleo Sci 60(3), 127-132.

Norrish and Dwyer, 2005
Norrish MI, Dwyer KL. 2005, Preliminary investigation of the effect of peppermint oil on an objective measure of daytime sleepiness. Int J Psychophysiol. 55(3), 291-8.