Association between the serotonin transporter polymorphism (5HTTLPR) and subjective happiness level in Japanese adults
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An epidemiological study in the USA recently reported that variations in the serotonin transporter gene-linked polymorphic region (5HTTLPR) can influence subjective well-being or happiness; specifically, individuals with long polymorphisms (L-allele carriers), associated with increased serotonin reuptake activity, reported significantly higher levels of life satisfaction compared to individuals with short polymorphisms (S-allele carriers). It is empirically known that an international discrepancy in subjective well-being exists, which may be linked to findings that the genotype distribution is different in the USA and Japan. Thus, we investigated the association between 5HTTLPR and happiness in Japan to examine whether geographical heterogeneity of well-being could be partly explained by variations in 5HTTLPR.
Ninety-two healthy Japanese individuals were recruited (34 males and 58 females; age range, 19-40 years). Subjective happiness was evaluated using the Japanese version of the Subjective Happiness Scale. Regression analysis examining the association between 5HTTLPR and subjective happiness level revealed that L-allele carriers report a significantly higher level of subjective happiness.
In concurrence with the epidemiological findings of the USA, this study indicates that 5HTTLPR is associated with subjective happiness levels in Japanese adults. In turn, this might provide some insight into the potential mechanism underlying international differences in subjective well-being or happiness.
KeywordsSubjective happiness level 5HTTLPR Population genetics Serotonin transporter
Body mass index
Japanese version of the subjective happiness scale
Perigenual anterior cingulated cortex
Serotonin transporter gene-linked polymorphic region.
Happiness is one of the most fundamental human goals, which has led researchers to question the source of individual happiness. Interestingly, an epidemiological study in the USA recently reported that individual heterogeneity in subjective well-being or happiness might be partly explained by variations in the serotonin transporter gene-linked polymorphic region (5HTTLPR) (De Neve, 2011), which are known to impact the expression and function of serotonin transporters (5HTT) (Hariri et al. 2002; Heinz et al. 2005). Specifically, it was found that individuals with long polymorphisms (L-allele carriers), associated with increased serotonin (5HT) reuptake activity, report significantly higher levels of life satisfaction compared to individuals with short polymorphisms (S-allele carriers) (De Neve, 2011). Although the follow-up work conducted by the same author and colleagues failed to replicate the original finding (De Neve et al., 2012), the 5HTT gene may be a good candidate gene for subjective well-being or happiness. Indeed, polymorphisms might be related to affective disorders, whereby S-allele carriers are more sensitive to negative emotional stimuli and have a higher susceptibility for depression and anxiety-related disorders compared to L-allele carriers (Lesch et al. 1996; Caspi et al. 2003; Ohira et al. 2009).
It is empirically known that an international difference in subjective well-being exists (Diener et al. 1995; White, 2007); for example, South Korea and Japan report below average levels of happiness and life satisfaction compared to other countries, while the USA reports above average levels (Diener et al. 1995). Given the previous finding that the genotype distribution of 5HTTLPR is different in the USA (SS: 26%, SL: 49%, LL: 25%) (Pluess et al., 2010) compared to Japan (SS: 57.8%, SL: 37.8%, LL: 4.4%) (Mizuno et al., 2006), we speculated that the geographical heterogeneity of subjective well-being or happiness might be partly explained by variations in 5HTTLPR. In other words, since S-allele carriers are more prone to depression, L-allele carriers might evaluate their lives more positively. The significantly lower level of L-allele carriers in Japan compared to the USA might, in turn, explain the below average level of happiness and life satisfaction reported by the Japanese population. Thus, in this study, we attempted to elucidate the association between 5HTTLPR and happiness in Japanese adults.
Results from the regression analysis examining the association between 5HTTLPR and subjective happiness level
Frequency of alcohol intake
Adjusted R 2
In concurrence with the epidemiological findings in the USA, the present study indicates that 5HTTLPR is associated with subjective happiness levels in Japanese adults, although this study is small-scale, with 92 individuals, as compared to the current standards in behavioral genetics. Given the difference regarding genotypic distribution in the USA and Japan, this finding provides some insight into the potential mechanism underlying international heterogeneity of subjective well-being or happiness. However, while the data offer a genetic explanation for subjective happiness, the underpinning association between 5HTTLPR and subjective happiness remains obscure. One speculation may be that brain functions are influenced by 5HTTLPR.
Recent neuroimaging studies have indicated that the default mode network, which includes the medial prefrontal cortex, perigenual anterior cingulate cortex (pACC), posterior cingulate cortex, and superior temporal gyrus, is implicated in episodic memory retrieval, theory of mind, and prospection (vision of the future) (Buckner and Carroll, 2007; Nakao et al. 2012; Heine et al. 2012). Previous reports have suggested that the default mode network may be functionally important for the evaluation of subjective happiness because our assessment of subjective happiness relies heavily on our memories, future plans, and self-reflection (Berridge and Kringelbach, 2011). Interestingly, previous studies have indicated that 5HTTLPR can influence structural properties of the default mode network. For example, the gray matter volume of the pACC is significantly reduced in S-allele carriers compared to L-allele carriers (Pezawas et al. 2005). Functional and structural magnetic resonance imaging studies have demonstrated that high gray matter volume within specific brain regions is linked to elevated function (Giménez et al. 2004; Hamzei et al. 2012); thus, reduced gray matter volume in the pACC of S-allele carriers might influence their evaluation of subjective happiness. However, further studies are required to corroborate this postulation.
This study was supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (25750354 to MM). The funders had no role in study design, data collection, analysis, decision to publish, or preparation of the manuscript.
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Open AccessThis article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.