1. Introduction
Family has an important role in providing models of behaviors and shaping the tobacco practices, values, beliefs and attitudes of children and adolescents [
1,
2,
3]. Children learn to construct their reality based on early experiences in their environment, peer behaviors and cultural norms [
2,
4]. The effect of parental smoking on children’s smoking has been well documented [
5], but there have been differences found regarding whether a mother’s or father’s smoking is a more important risk factor and regarding whether the effect varies based on the child’s gender [
6,
7,
8,
9,
10]. In their systematic review and meta-analysis, Leonardi-Bee
et al. [
5] concluded that having two smoking parents increases the child’s smoking risk compared to having just one smoking parent. They also concluded that a mother’s smoking is a slightly more prominent risk factor than a father’s smoking (OR 2.19
vs. OR 1.66). They also provided some evidence of a sex-specific effect in which boys were more substantially influenced by paternal smoking, while girls were influenced more by maternal smoking.
Despite the vast evidence of the parental influence on smoking initiation, the influence of grandparents’ smoking and the intergenerational transmission of smoking behavior beyond two generations have rarely been studied [
6,
7]. However, the increased life expectancy of both men and women in industrialized countries [
11] means that grandparents live longer and have more opportunities to witness their grandchildren’s development from early childhood to adolescence and even adulthood and thus their smoking may play a role in the initiation of smoking among their grandchildren. Escario and Wilkinson [
12] showed that smoking by at least one grandparent living in the same family as grandchildren increases the odds of smoking for boys but not for girls. A study from the U.S. examined the smoking behavior across three generations and showed that smoking behaviors are transferred from preceding generations to later generations and that parents have a mediating role in this process [
8]. There are no published studies in which the effects of maternal and paternal grandparents’ smoking on grandchildren’s smoking have been studied separately; nor have there been studies on the use of tobacco or tobacco-like products other than cigarettes. In this study, other tobacco or tobacco-like products include snus, water pipes and electronic cigarettes, and the shorter term “other tobacco products” will be used to encompass these products, although electronic cigarettes do not actually contain tobacco.
In this study, we addressed the transmission of smoking across three generations. The research questions were as follows:
- (1)
Are maternal and paternal grandmothers’ and grandfathers’ smoking related to their grandchildren’s smoking and use of other tobacco products?
- (2)
Is the influence of grandparents’ smoking independent of parents’ smoking or is it mediated through parental smoking behavior?
In addition, we studied the relationship of mother’s and father’s smoking to their children’s smoking and use of other tobacco products as well as differences between genders.
4. Discussion
The results of this study demonstrate the association between grandparents’ smoking and their grandchildren’s tobacco use. The association was noted for both paternal and maternal grandparents and for experimentation, daily smoking and use of other tobacco or tobacco-like products. The transmission of smoking from grandparents to grandchildren was mainly mediated through mother’s and father’s smoking, which were also strongly related to children’s tobacco use. One-third of the effect from grandparents was direct, not mediated through the parents. Children having two smoking parents or paternal or maternal grandparents were more likely to smoke, as were those with formerly smoking parents or grandparents.
The association between children’s and their grandparents’ smoking and the mediation effect of parents’ smoking are consistent with the study by Vandewater
et al. [
8], which is the only report studying three generations and all grandparents and not only those who live in the same family with their grandchildren. Our study adds to the previous knowledge by showing that there seems to be a direct effect of grandparents on adolescent smoking behavior and that both the paternal and maternal grandparents are important.
A number of mechanisms, both social, psychological, and genetic, have been proposed to explain the influence of parents’ smoking on their children’s smoking. These mechanisms are likely to be valid, at least partly, in explaining the influence of grandparents’ smoking behavior as well. The social and psychological mechanisms include direct modeling of behavior, in which parents and grandparents serve as role models, the transmission of norms and attitudes towards smoking, and (grand)parenting styles like a home smoking ban and controlling access to tobacco products and to certain friendship networks [
15,
16]. Genetics and biological pathways have also been shown to have a role in smoking behavior and nicotine addiction [
17,
18] and the role of second-hand smoke should not be forgotten [
19]. Both genetic and environmental factors can explain smoking initiation and quantities of cigarettes smoked and environmental factors can regulate the expression of genetic predisposition [
18,
20]. Interestingly, non-biological stepparents’ smoking has been shown to influence adolescents’ smoking as significantly as parents’ smoking [
21], supporting the important role of social and environmental factors.
With the increasing life expectancy, children have more possibilities to spend time with their grandparents, explaining why their influence on different aspects of children’s life is likely to be higher than in previous decades. In Finland, where this study was conducted, 30% of 12-year-old children had all four grandparents alive in 2011 [
22]. A majority of grandparents actively provide childcare for their grandchildren in Finland [
23]. The evidence also suggests that the intergenerational influences and transmission of values, attitudes, and patterns of behavior between grandchildren and grandparents today are strong, despite changes in the society as a whole and in terms of family structure and socioeconomic context [
24,
25,
26]. Grandparents’ possible role in adolescent smoking prevention programs is worth studying because family interventions have been shown to have positive effects [
27].
Finland is an interesting context to study the effect of family smoking because of its strict smoking prevention legislation [
28]. All advertisement and sales promotion are forbidden, sales of tobacco products to minors under the age of 18 is forbidden, tobacco products are not displayed in retail sales, and smoking is not allowed in public places, restaurants, cafés, workplaces, schools and in places which minors can access. This means that the exposure within the family may be more influential in a Finnish society than in a society where smoking and tobacco products are easily seen and accessed by minors, and where tobacco industry can advertise their products. Cross-country comparisons could bring valuable insights into the mechanisms of the intergenerational transmission of smoking and into the actions needed to prevent it. In countries with strong tobacco control policies, family smoking could be one of the remaining issues to tackle and mostly with other means than legislative bans and restrictions (e.g., family interventions and smoking cessation support in health care). Countries with less comprehensive tobacco control policies could benefit from stronger implementation of the Framework Convention on Tobacco Control (FCTC) as the first-stage prevention.
Some limitations of our study should be noted. The data are based on adolescents’ self-reports, and we cannot know how accurately they have reported their grandparents’ smoking. Conversely, adolescents’ reports reflect their perceptions of their grandparents’ smoking, which can be considered even more important than the actual grandparent’s smoking status. We also do not know what close contact, if any, the children had with their grandparents; this information would have provided more insight into the role of grandparents and may have modified the observed effects. When children or grandchildren are asked about grandparents’/parents’ smoking, the exposure to environmental tobacco smoke during early childhood may be omitted, which may dilute the effects in our study. We did not have information on the age of parents or grandparents which may have been relevant because smoking has diminished in these age groups. On the other hand, we have shown that the strength of the association between the parents’ and child’s smoking did not change over a period of three decades [
29] which is why the lack of age information hardly produces any bias. Important factors in the initiation and continuation of smoking are siblings’ and peers’ smoking [
5] which were not available in our data. The low response rate may alter the generalizability of this study, although the indirect non-response analysis did not suggest any bias in the adolescents’ reports of their grandparents’ smoking.