Many earlier studies have shown a relationship between an individual’s mortality and the number of children he or she has. Generally, the childless have higher mortality than those with children, and those with only one child have higher mortality than those with two. Some authors have also reported an increasing mortality as the number of children exceeds four or five [1–3], while other studies, including one from Norway [4], have shown no such disadvantage at high parities. These relationships have been thought to reflect physiological effects of pregnancies (for women) as well as various types of social effects of having children. For example, children may be a source of emotional satisfaction, and above a certain age they may exert control on parents’ behaviour and provide care and assistance, which may reduce mortality. On the other hand, parenthood may also lead to stress because of economic worries or concerns about the children’s wellbeing. Moreover, there are selective influences: several factors of importance for fertility also affect later health and mortality through other channels. The social effects of parenthood probably vary with the characteristics of the children, such as their personality, education, economic resources, health, and family situation. The children’s sex may also have some importance as a conditioning factor.
Few studies have addressed the effect of children’s sex composition on parents’ mortality, and most of them have considered pre-industrial populations. Using data on Sami women from northern Scandinavia, Helle, Lummaa and Jokela [5] find that having sons increases a woman’s mortality, whereas having daughters has the opposite effect. However, later studies have failed to consistently replicate these results and have usually found identical, or almost identical, effects of sons and daughters on women’s mortality e.g. [6–9]. There has been little research into whether the sex composition of the children affects parents’ mortality in western contemporary societies. A study by Jasienska, Nenko and Jasienski [10] concludes that daughters reduce men’s mortality whereas both sons and daughters increase women’s mortality, and do so to the same extent. However, this investigation includes only 102 women and 163 men born between 1894 and 1937. It also only includes people who had already died at the time of study and had at least one son and one daughter, and excludes those who were single or remarried. Studies based on larger and more representative samples are lacking.
One could argue that there might be diminishing marginal returns to having children of a single sex. For example, even if having one son might benefit the parents and their health, having a second or third son might be less important. Perhaps they would be better off having at least one daughter, who might give them other benefits. In fact, many parents seem to have a preference for mixed-sex offspring. An indication of such sex preferences, is that in the Scandinavian countries there is no effect of the sex of the first born on the probability of having a second child and subsequent fertility is slightly higher among those who have two children of the same sex than those who have one boy and one girl. However, a slightly stronger preference for daughters seems to have developed over the last two decades [11]. This means that Scandinavians still prefer to have at least one child of each sex but now consider it to be more important to have at least one girl than at least one boy.
The purpose of this study is to explore the relationship between children’s sex composition and parents’ mortality in a Nordic setting. The analysis is based on discrete-time hazard models, estimated for the years 1980–2008 for women and men born after 1935 using register data that encompasses the entire Norwegian population. As suggested by earlier studies [10], the effect of a certain sex composition is not necessarily the same for mothers and fathers, so the models are estimated separately for women and men. Furthermore, the effect may vary with certain characteristics of the parents. For example, among those who have support from a spouse, the practical assistance that daughters have often provided may be less crucial. In this study, the conditioning effects of age, education, marital status, age at first birth and period are considered.
Little attention has been devoted to the conceivable underlying mechanisms in the few earlier studies that have addressed the link between children’s sex and parents’ mortality. This paper therefore includes a quite thorough discussion of potential causal effects and selective influences, as well as the variations in these.
Parenthood influences the well-beinga and lifestyle as well as economic decisions of the parents. Some of these influences may be contingent on the sex of the child.
A few studies have looked into how the gender composition of children affects lifestyle choices. They have found that having an additional daughter reduces the probability of having an alcohol or drug problem, or smoking [12], and that mothers of first-born daughters weigh less than mothers of first-borns sons. However, fathers whose first-born was a daughter weigh more than a father who’s first-born was a son [13].
It can also be hypothesised that it is more stressful to bring up boys. They are more likely to be hyperactive or diagnosed with attention deficit disorder or autism. More importantly, even boys without any disorders are often seen as more boisterous, noisy and less well behaved than girls. At later ages boys have in recent decades been more likely to drop out of school and be unemployed, which may worry the parents. Moreover, bringing up sons may entail a higher level of economic stress. Studies have found that boys receive more pocket money than girls and that boys consumption is considered more important by parents [14, 15]. A survey by a British bank [16] showed that boys cost on average 23% more to raise than girls.
A US study [17] report that the birth of a son induces a man to increase the number of hours worked more than does the birth of a daughter. Similarly, research employing German data finds that having a first-born son increases fathers’ working hours compared to having a first-born daughter [18]. Moreover, both these studies find that fathers of boys have a higher wage rate than fathers of daughters, so the income advantage of the former is even larger than suggested by difference in working hours. Although fathers of sons work longer hours, there is no evidence that this happens at the expense of time spent with their children. On the contrary, fathers have been found to spend more time with their children – also with their daughters – when they have at least one son, and more time with their sons than with their daughters [19–21]. Even in a gender equal society like Sweden, fathers take out more parental leave following the birth of a son [22].
A much cited study using US data found that having sons reduces the risk of divorce [23]. Later research has, however, failed to consistently replicate this result. For example, a study employing data from 18 countries [24] reveals no difference between one-child couples with a son and one-child couples with a daughter. They do however find that two-child couples with children of the same sex, whether girls or boys, have higher divorce risks than those with one child of each sex, and that sons slightly lower divorce risks in three children families. A Swedish study reports the lowest divorce risk in mixed-sex two-child families, whereas the divorce risk at parity three rises with increasing number of girls [25].
Old people tend to have more social contact with daughters than sons [26, 27] and daughters are more likely than sons to provide care to their elderly parents. However, some studies report that the elderly receive more help from a child of the same sex, and that the reason why women are overrepresented as caregivers is that there are more women than men among the elderly due to men’s higher mortality [28].
All of the effects mentioned above probably have implications for the health of the parents and ultimately their mortality. For example, a higher weight (possibly linked to having sons, for mothers) is a risk factor for several potentially fatal diseases. Working long hours, such as fathers of sons are more inclined to do, may affect health adversely. It has been shown to increase the risk of coronary heart disease and depression [29–31]. Furthermore, men’s possibly stronger involvement with their children if there is a boy in the family may be beneficial for the fathers, as well as for the mothers, in the long run. Even more importantly, divorce – which may also be linked to children’s sex – is strongly associated with mortality (e.g. [32]). Finally, the amount of social support, which daughters are particularly likely to supply to their ageing parents, may affect mortality [33]. Studies based on measurements of subjective health have yet to provide a clear picture. Powdthavee, Wu and Oswald [12] conclude that having an additional daughter induces people to report better subjective health, whereas (in a Middle East setting) Engelman, Agree, Yount and Bishai [34] find a negative association between the number of daughters and reported physical functioning, especially for men.
A few studies have looked at the effect of children’s sex on parents’ well-being. One investigation employing Danish data reports a positive effect on fathers’ well-being if the first-born was a boy [35]. Another study finds that mothers of only sons are the happiest, and that those with a majority of boys display higher levels of happiness than those with other sex compositions of children [36]. Finally, a study reports that fathers of boys are more likely to be happily married [37], which in turn heightens the protective effect of marriage (e.g. [38–40]).
In addition to all of these social effects of having children of a given sex, there are physiological implications for the mother of giving birth to sons. Male foetuses have higher intrauterine growth rates and birth weights and therefore require more maternal energy [41–44]; and women carrying male foetuses experience higher levels of testosterone, which is an immunosuppressant [45, 46].
Possible variations in the importance of children’s sex
The potential effect of a given sex composition may be conditional on a variety of other factors. I consider these possible conditioning effects by stratifying according to a few characteristics (of the parent): age, period, marital status, education and age at first birth.
The importance of children as caregivers increases with parents’ age, and having at least one daughter may therefore become increasingly advantageous with age. The same is true of the role of a daughter as a source of social contact.
Besides age, marital status may also have an effect on the need for social contact with and help from the children, often daughters, as having a spouse can be a substitute when it comes to practical help and companionship. A wife or husband can also make the partner adopt a healthier lifestyle (e.g. cut down on smoking and drinking) in the same way as children, especially daughters often do.
Education is another possible conditioning factor. The more highly educated have a healthier lifestyle, which means that any pressure concerning life-style changes by children, and especially daughters, will be less important. However, one study [47] found that the highly educated women have a higher preference for girls, which assuming they assess correctly how important a daughter is to them, may mean that having at least one daughter is especially beneficial for this group.
Having a child at an early age is detrimental to health later in life. The effect might be dependent on the sex of the child. Women who become mothers at a very early age, especially teenage mothers, are less likely to be in a relationship with the child’s father or have contact with the father at all. They are also likely to take less education [48]. Having had sons may have been particularly stressful for these women, as sons often require more attention than daughters and are more costly.
Finally, the effect of having a certain sex composition may vary over time. For example, the education of the children has in some studies been shown to have a protective effect on parents’ mortality [49–51], and a few decades ago sons tended to be more educated than daughters. The difference between the sexes in these respects are now much smaller.
