No Evidence That Hormonal Oral Contraceptives Affect Chemosensory Perception

No Evidence That Hormonal Contraceptives Affect Chemosensory Perception. Martin Schaefer at al. i-Perception, February 1, 2021. https://doi.org/10.1177/2041669520983339

Rolf Degen's take: Contrary to previous assumptions, oral contraceptives do not affect women's smell or taste perception

Abstract: The use of oral contraceptives (OC) in the form of a hormonal pill has been widespread for decades. Despite its popularity and long-time use, there is still much ambiguity and anecdotal reports about a range of potential side effects. Here, we addressed the potential effect of OC use on chemosensory perception. Previous research has almost exclusively focused on olfaction, but we expanded this to the trigeminal system and the sense of taste. We used Bayesian statistics to compare the olfactory, trigeminal, and taste detection abilities between a group of 34 normal cycling women and a group of 26 women using OC. Our results indicated that odor, trigeminal, and taste thresholds were not affected by the use of OC. Moreover, neither odor perception, nor taste perception was affected; all with Bayes factors consistently favoring the null hypothesis. The only exception to these results was odor identification where Bayes factors indicated inconclusive evidence. We conclude that effects of OC use on chemosensory perception are unlikely, and if present, likely are of no to little behavioral relevance.

Keywords: oral contraceptives, chemosensory perception, Bayesian, olfaction, trigeminal, taste, the pill

Discussion

Previous research investigating the effect OC on olfactory sensitivity has been inconclusive. Odor sensitivity has previously been shown to be both positively and negatively affected by pill use, positively and negatively affected by duration of pill intake, and potential differences seem to have been odor-dependent (Derntl et al., 2013; Kollndorfer et al., 2016; Lundström et al., 2006; Renfro & Hoffmann, 2013). Here, we revisited the question of whether OC use affects olfactory performance as well as assessed potential effects of OC use on trigeminal and taste perception. Our results indicate that OC use does not impact chemosensory perception. In fact, we considered a wide range of priors, and the null hypothesis (H0) was consistently favored over the alternative hypothesis (H1). Importantly, as trigeminal thresholds were not affected by OC, the mixed results from earlier research likely do not depend on differences in odor trigeminality of the odors used. Also, the only measure that indicated a potential effect of OC in our data was not a sensory function, but a measure that can be considered as more cognitive (cued odor identification). Notably, women have been shown to outperform men in odor identification—an effect not thought to be mediated by differences in olfaction but rather in general language abilities (Larsson, 1997, 2002; Larsson et al., 2005, 2014). A recent meta-analysis on the effect of OC on cognition further demonstrated that there is little evidence that OC impacts cognitive functions with consistent evidence only demonstrated for verbal memory (Warren et al., 2014). These findings indicate that any potential effect of OC on odor identification may be due to an impact on language functions and not olfactory function per se.

The current study has, however, weaknesses including a rather small sample size of participants in each group (OC users and nonusers), thus making it difficult to reach definite conclusions due to low statistical power. Post hoc power calculations revealed that we had 0.47 power to detect a medium effect size (0.5 d) at alpha level .05 (Faul et al., 2007). Another limitation is that the type, and dosage, of the hormonal contents of the used OC varied, and we could not control the duration of OC intake. Both the dosage of the ethinyl estradiol content, and the duration of OC use, have been suggested to alter how OC usage impacts olfactory sensitivity (Derntl et al., 2013; Kollndorfer et al., 2016). Future research should take this into account and also test a wider range of odorants, tastants, and trigeminal compounds. We tried to minimize the limitation in number of stimuli by including ecological relevant stimuli (food and non-food-associated odors) as well as use different chemical compositions (monomolecular odors and mixtures). Despite these short comings, we argue that our findings are strengthened by the following points. Earlier studies have only used frequentist statistics and were not able to test the strength of the H0 in instances when no differences were found (Dienes, 2014). Moreover, previous studies have found an effect of OC use on olfactory sensitivity when assessing very specific outcomes (e.g., the sensitivity for a specific odor, the influence of hormone dosage of the OC content, the duration of pill intake, which menstrual phase the women in the control group were in, etc.), with no general or broader effects consistently shown.

In summary, we conclude that an effect of OC use on chemosensory perception is unlikely and, if present, presumably of a small effect size with negligible ecological relevance. This should come as good news to OC users as based on these results there is no need to be concerned about altered chemosensory perception.