Smoking cessation is not associated with a decline in reported sleep bruxism in middle-aged Finnish twins: Data revisited

A recent cross-sectional study among 8410 Finnish adult twins showed substantial correlates of behavioural and lifestyle factors with sleep bruxism (SB).1 The role of genetic factors, based on twin correlations, was relatively modest, suggesting that environmental factors may play a major role in SB aetiology. Notably, smoking status and nicotine dependence were strongly and significantly positively associated with SB. Another longitudinal study among these Finnish twins revealed that SB was quite stable over a 20-year span, slightly more so in men than in women.2 Evidence was found for a moderate genetic component of SB over time based on greater similarity in monozygotic than dizygotic pairs, both cross-sectionally and in the cross-twin cross-time analyses. The authors concluded that SB, even as a self-reported phenomenon, seems to have trait persistence in addition to genetic liability. Smoking is one of the most detrimental behaviours underlying diseases associated with health problems and mortality across populations.3 Therefore, efforts to decline tobacco use and smoking cessation have been globally implemented during the past decades. Also in a recent study based on follow-up of the Finnish twin data on SB and mortality over a 30-year period, it was found, when adjusted for all studied covariates known as risks for later health and death and when analysed separately, that smoking emerged as the most significant risk for mortality.4 It was concluded that, although SB in itself is not a risk factor, frequent SB may reflect an underlying condition or behaviour detrimental to health. Bearing in mind the above-mentioned role of environmental factors in the aetiology of SB, the aim of the present study was to examine whether smoking cessation is associated with changes in self-reported SB in a 21-year period among Finnish twins. We assumed a decline in weekly SB in those quitting smoking compared to those who continue to smoke. Of the 4992 twins who had responded to the bruxism questions both in 1990 and in 2011, altogether 394 reported bruxism weekly in 1990, and 86 of them were current smokers. We analysed their bruxism status in 2011 and whether smoking cessation during 1990–2011 was associated with it, using a modified Chi-square test to correct for a sampling of twins within pairs. Collection and categorization of the twin data have been previously reported in detail.1, 2, 4 About one-third (30) of weekly bruxers in 1990 (86) had quit smoking by 2011. No difference was found in SB status in 2011 between those who had quit and those still smoking. The results are shown in Table 1. Slightly more men (38%, 14/37) than women (33%, 16/49) quit smoking by 2011. Their mean age in 2011 was 59.5 years (SD 3.7, range 54.3–66.8). Due to the small number of twins here, the results must be interpreted with caution. However, our hypothesis was rejected. It may be that quitting smoking does not affect SB behaviour in middle aged. The probable trait persistence of SB and its genetic liability of it should be borne in mind. Studies on younger and larger populations are welcome. JA and JK conceived the study and drafted the manuscript. JK analysed the data. FL, CH and MP critically revised the manuscript. All authors approved the final version. The authors received no funding for the present study. None of the authors declares any conflict of interest. The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer-review/10.1111/joor.13524. FTC data are not publicly available due to informed consent restrictions. However, FTC data are available from the Institute for Molecular Medicine Finland (FIMM) Data Access Committee (DAC) ([email protected]) for authorised researchers with IRB/ethics approval and an institutionally approved study plan. To ensure the protection of privacy and compliance with national data protection legislation, a data use/transfer agreement is needed, the content and specific clauses of which will depend on the nature of the requested data. Full results of the present study are available from the authors upon request.