6.2.1 Alcohol use and periodontal pockets: findings of cross-sectional studies (I and II)
Association between alcohol use and periodontal pockets (Study I)
Although different alcohol use measures (amount, frequency, and use over the risk limit) were used in the study, there was no consistent association of any of these measures with the number of teeth with deepened (≥4 mm) periodontal pockets. This finding is in agreement with the previous finding by Okamoto and co-workers, who reported that alcohol intake was not associated with periodontal disease development, measured by the Community Periodontal Index (CPI) scores (Okamoto et al., 2006). On the other hand, these findings are in contradiction to previous studies that have reported high amounts of alcohol intake to be associated with periodontal pocket depth (Sakki et al., 1995; Nishida et al., 2004;
Shimazaki et al., 2005; Nishida et al., 2010; Kim et al., 2014) and periodontal disease (Wang et al., 2016).
In line with this study’s hypothesis, age, gender, and education-stratified analyses modified the association of alcohol use measures with the number of teeth with deepened (≥4 mm) periodontal pockets (Figure 6). The age-stratified analyses suggested that among older people (50‒65 years), there was a weak positive association of alcohol use (amount and use over the risk limit) with teeth with deepened periodontal pockets (Figure 6). This finding is partly in agreement with another Finnish study conducted among 55-year-old adults, which suggested an association between alcohol use and poor periodontal health among older people (Sakki et al., 1995). In contrast, a study conducted among Nigerian adults aged 50 years or older did not report any significant association of alcohol consumption (amount or frequency) with periodontal disease (Akpata et al., 2016). One essential difference between the latter study and this study is that age restrictions were carried out in this study in order to control for age-related confounding.
It is worth noting that in the present study, the association of alcohol use (amount, frequency, and use over the risk limit) with deepened periodontal pockets among older people was found only in less educated adults (basic or intermediate educational groups). The lack of association in the higher educated group supports the view that the often-observed association between alcohol use and poor periodontal condition is due to confounding and possibly related to behavioral factors.
Gender-stratified analyses suggested that among men, in contrast to women, alcohol use (amount, frequency, and use over the risk limit) was weakly associated with the number of teeth with deepened periodontal pockets (Figure 6). This finding is in agreement with the report by Kim and colleagues, who
health (Hobdell et al., 2003a; Bernabé et al., 2011). To date, this is the first study to systematically investigate the role of SEP (education) in the association between alcohol use and periodontal condition. Currently, there are a limited number of studies that have examined this association in one SEP group (SEP indicated by employment) (Shizukuishi et al., 1998; Pitiphat et al., 2003; Nishida et al., 2004; Nishida et al., 2010). The finding of the present study—that the detrimental effects of alcohol use on periodontal condition were evident only in less educated adults (basic or intermediate education)—emphasized that alcohol effects are dependent on one’s SEP. Similar results have been reported with regard to the prevalence (Shizukuishi et al., 1998; Nishida et al., 2004) and progression (Nishida et al., 2010) of periodontitis among Japanese factory workers. It is interesting that the latter cross-sectional (Nishida et al., 2004) and longitudinal (Nishida et al., 2010) studies also showed the role of genetics; researchers reported that the presence of a particular aldehyde dehydrogenase (ALDH2) genotype could explain the variation of the effects of alcohol use on periodontal health. Contrary to the findings of those studies and the present study, another study reported that alcohol use among male healthcare professionals (higher educated) was associated with self-reported periodontitis (Pitiphat et al., 2003).
Association between the types of alcoholic beverages/gamma-glutamyltransferase (GGT) and periodontal pockets (Study II)
In contrast to the hypothesis of this study, neither the amount nor the frequency measures of any of the alcoholic beverages associated consistently with the number of teeth with deepened (≥4 mm) periodontal pockets in the total population (Figure 6) or among non-smokers. This observation is in agreement with earlier findings of cross-sectional studies (Tezal et al., 2001; Akpata et al., 2016) and a four-year longitudinal study by Pitiphat et al. (2003), which suggested that no statistically significant association exists between the intake of different types of alcoholic beverages and periodontal health.
One interesting finding in this study was that the frequency of spirit intake among non-smokers was associated with teeth with deepened periodontal pockets only in the education-stratified analyses. Among the frequent spirit drinkers, this association was positive among less educated participants, whereas it was inverse among highly educated participants. In contrast to the findings related to the frequency of spirit intake, the frequency of beer intake was inversely associated with teeth with deepened periodontal pockets among less educated participants, but positively associated among highly educated participants. Although most of the above-mentioned findings were statistically non-significant, the findings among highly educated beer drinkers is partly in agreement with the reports by Pitiphat et al. (2003), which suggested a weak but statistically non-significant association of beer intake with periodontal condition among healthcare professionals, and another report by Tezal et al. (2004), which suggested a harmful effect of beer and hard liquor on periodontal health.
Additionally, the data showed no association of GGT levels with the number of teeth with deepened periodontal pockets, irrespective of the smoking status and SEP of the participants. This finding supports the findings of cross-sectional studies (studies I‒II) in this dissertation about the lack of association between alcohol use measures and the number of teeth with deepened periodontal pockets. However, this finding is in contrast to the results by Khocht and co-workers (Khocht et al., 2003), who reported that a high level of GGT >51 IU/L (alcohol dependence) is associated with a deterioration in periodontal health. One explanation for the difference in the results is the characteristics of the study population; the study by Khocht and co-workers included a relatively small sample size of 40 alcohol dependent persons without medical disorders, whereas the Health 2000 Survey is sampled from a general population. The differences in study population as a cause for conflicting findings is supported by the fact that in the study by Khocht and co-workers, around 46% of the participants had GGT levels >51 IU/L, compared to 15% in the present study population.
6.2.2 Alcohol use and periodontal pockets: findings of longitudinal studies (III and IV) Association between alcohol use and four-year periodontal pocket incidence (Study III)
Analogous to the cross-sectional findings, the finding that there was no consistent association between any of the alcohol use measures (amount, frequency, and use over the risk limit) at baseline and development of deepened (≥4 mm) periodontal pockets at follow-up in the total population is contradictory to the hypothesis of this study. In line with this finding, a previous longitudinal investigation reported no association between alcohol use and the development of periodontal disease, measured by the CPI (Okamoto et al., 2006). In contrast, another longitudinal study reported that there is a positive association between alcohol use and self-reported periodontitis development (Pitiphat et al., 2003). Although there are studies that have a longitudinal study design, only findings from these two above-mentioned studies can be compared with the present study, because the study population in those studies and in the present study included only periodontally healthy individuals at baseline. This is particularly important, because the inclusion of prevalent disease cases at baseline can underestimate the actual effect (Heaton et al., 2014).
Since the previous studies investigating the incidence of periodontal disease in relation to alcohol use were performed among men (Okamoto et al., 2006; Pitiphat et al., 2003), gender-stratified analyses were conducted to compare the findings among men and women. Contrary to the positive association in men reported by those above-mentioned studies, it was found that, in the present study, alcohol use (higher amount or use over the risk limit) at baseline was weakly associated with the incidence of deepened periodontal pockets among non-smoking women, but not among non-smoking men (Figure 7).
One interesting finding was that alcohol use (amount, frequency, and use over the risk limit) was weakly associated with teeth with deepened periodontal pockets among non-smoking men in a cross-sectional setting (Figure 6). In a longitudinal setting, this association was found among non-smoking women, but only when alcohol was consumed in higher amounts or over the risk limit at baseline (Figure 7). Even though the use over the risk limit variable was gender specific, the long-term effects of alcohol use over the risk limit on periodontal condition was more pronounced in women than in men. Based on this finding, it can be assumed that women have a lower threshold compared to men to suffer from the detrimental effects of the use of alcohol either long-term or over the risk limit. One possible explanation for this could be the difference in alcohol pharmacokinetics among men and women. Studies have suggested that, compared to men, lower body weight or lower volumes of body water or even lower rates of alcohol metabolism in women may increase the blood alcohol concentration, meaning that women could experience the same detrimental effects as men even with lower amounts of alcohol (Baraona et al., 2001;
Wilsnack, Wilsnack & Kantor, 2013).
On the other hand, it can be speculated that an association found in the cross-sectional studies among men, but not among women, could be explained by the differences in drinking behavior between men and women. It is generally known that men are more likely to consume alcohol in heavy amounts and more frequently than women (Wilsnack et al., 2009). Conflicting findings about the gender-specific effects of alcohol use on periodontal health exist (Susin et al., 2015; Wu et al., 2013; Park et al., 2014; Wagner et al., 2017). Research has shown that the effects of alcohol use on health differ by gender (Wilsnack, Wilsnack &
Kantor, 2013),but the mechanism underlying these differences is still largely unclear.
Association between alcohol use and 11-year periodontal pocket incidence (Study IV)
Similar to the four-year follow-up study, no consistent association was found in the total population between alcohol use measures (amount, frequency, and type of beverage) at baseline and the development of deepened (≥4 mm) periodontal pockets (dichotomous outcome) during the follow-up period. This finding is contradictory to the hypothesis of this study (Figure 7). This finding is in line with a study that reported no association (Okamoto et al., 2006), while partly in contrast to another study that reported a positive association (Pitiphat et al., 2003). The latter study suggested no clear association between the type of beverage and periodontal disease (Pitiphat et al., 2003), which is in line with the findings about the type of beverage in the present study when the outcome is dichotomous.
When the outcome was a count variable, namely the number of teeth with deepened periodontal pockets, an inverse association was seen with frequency (alcohol or type of beverage) but not with the amount of alcohol use (Figure 7). The difference in the results between the count and the dichotomous outcome variables could be due to the fact that the dichotomous variable is more robust than the count variable. The difference in the results with regard to only frequency variables (alcohol or type of beverage) suggests a mechanism other than biological.
The smoking-stratified analyses did not reveal any consistent association between either the amount or the frequency of alcohol use with the dichotomous periodontal pocket outcome among smokers or non-smokers. However, when the outcome was a count variable, an inverse association was found between the frequency variable and the incidence of periodontal pockets among non-smokers. In comparison to the four-year follow-up study—in which the frequency of alcohol use had a positive association with deepened periodontal pocket incidence among smokers—the 11-year follow-up study suggested an inverse association between the frequency of alcohol use and deepened periodontal pocket incidence among non-smokers (Figure 7).
One explanation for the weak or null findings even in the longitudinal settings in the present study can be attributed to the good oral hygiene behavior of the participants (Table 3), which could possibly reduce the susceptibility to develop new cases. Considering the fact that periodontal disease is a multifactorial chronic disease, and the progression from gingivitis to periodontitis may vary based on several factors, it can be assumed that the good oral hygiene behavior of the participants may favor reversible periods of periodontal destruction and remission.