All over the world, men drink more alcohol and have higher rates of alcohol-related health problems and mortality than women . In fact the gender disparity in alcohol consumption is said to be one of few universal gender differences in human social behaviour . The global difference may be illustrated by the percentage of disability-adjusted life years (DALYs) attributable to alcohol by sex: in high-mortality developing countries like Algeria, Bangladesh, and South Africa: males 2.6% and females 0.5%; in low-mortality developing countries like Argentina, Indonesia, and Turkey: males 9.8% and females 2.0%; and in low-mortality developed countries like USA, Japan, and Sweden: males 14.0% and females 3.3% .
The different males versus females drinking patterns are the result of both biological and social factors . In this paper, the focus is on the gender system which refers to the societal structure organizing human activities and relations based on sex . Fundamentally, fathers have historically been responsible for supporting the family (the 'breadwinner position'), while mothers have been responsible for taking care of the children and the home (the 'caring position') . However, in the developed part of the world, many women have entered the public sphere of work, and some men have entered the private sphere of childcare. Our paper assesses alcohol-related consequences from a 'less gender-stereotypical division of parental duties' defined as a tendency among fathers to take on childcare duties and a tendency among mothers to take on 'breadwinner' obligations.
A basic theoretical concept in the paper is role theory, which generally explains human behaviour by expectations held by the individual as well as other people . From this a number of concepts have emerged such as role confusion (dilemma in deciding which role to take on), role conflict (tension due to incompatible roles), and role embracement (hold a role so much that the self disappears). Two common theories regarding roles and health regards stress and expansion . According to the stress theory  individuals with many activities and responsibilities experience more pressure, conflict and ill-health, because their primary role in life is so hard that additional duties risk health. The expansion theory contradicts this theory by suggesting that people with many roles have health advantages compared to others as they may compensate stress in one area with positive circumstances in other areas . Most research on multiple roles and health has been based on women in the United States and Europe, and conclude that several life roles are mainly beneficial for lifetime health [11, 12]. However, the relationship between the amount of roles and impact on health may also be curvilinear rather than linear; for example, a mother may begin to suffer from stress due to overwork instead of gaining from role expansion if the father does not take on his share of family and household duties [8, 13, 14].
One way of placing alcohol consumption in the context of role theory is that few roles (e.g. mother and housewife) may mean more time and opportunities to drink than if women have several roles (e.g. mother, housewife, friend, colleague, boss, and local politician). Moreover, gainful work for mothers may lead to lower rates of destructive behaviours including alcohol drinking through women having their own income, autonomy and social interaction , whilst childcare duties for fathers may translate to lower alcohol consumption through the satisfaction of adding closer relationships to their children . Yet, the expansion of roles and responsibilities via extra public work (mothers) and extra private duties (fathers) beyond a certain level may also be so stressful that both sexes could seek for relaxation through alcohol consumption [8, 15].
A further theoretical concept departs from the idea that a caring role may in itself be protective against risky lifestyles; the so called caring theory . That is, one reason women drink less and live longer lives could be that they have had the main caring role and that alcohol poses a risk to the child's health and security; for example, duties such as picking up from day-care or discos are not compatible with regular and risky alcohol drinking . Research shows that having dependent children implies a stronger protection for women than for men [18, 19], but if fathers/men take on a substantive caring responsibility for their children, this may well apply to them as well .
Correspondingly, a weakened caring role for mothers/women could lead to a loss of health-protective incentives. That is, when females enter traditionally male spheres of life, they may experience traditionally male health risks, including risky alcohol consumption through more opportunities and less restrictions . One reason that increased gender similarity in social positions has not implied gender similarity in lifestyles and alcohol drinking  is probably that women have retained the main caring (health-aware) position even after entering the paid labour market. Another explanation for findings indicating that women continue to drink less despite out-of-home employment may be that paid work has been measured by part-time work, which does not truly challenge the traditional division of the caring maternal position and the breadwinning paternal position .
Gender differences in a number of drinking measures have been examined by surveys in the general population in Europe (20–64 years, 2002) . In Sweden, the setting of the present study, the male to female ratios were: 1.8 (abstainers), 1.5 (overall frequency of drinking), 1.5 (quantity in grams of pure alcohol), and 3.2 (frequency of episodic heavy drinking). In order to understand gender-specific drinking patterns one should also consider how socioeconomic position and aspects of the wider society, such as the welfare system and level of gender equality, interacts with gender [14, 19, 24]. A Swedish study has, for example, reported that 'high alcohol consumption' as well as 'intense drinking' is highest in single men with low education living in rural areas, while the similar female proportion is highest in well-educated women in non-manual occupations in urban areas . Swedish alcohol consumption in around 1978, which was the historical start of our study period, was lower than it is today; 8.8 litres of 100% alcohol per inhabitant aged 15 years and over as compared to 10.4 litres in 2004 . During the same period the male to female ratio in various drinking measures has been quite stable (around 2.0). Gender differences in drinking patterns and social interactions imply gender differences in sickness, injuries, and deaths; for example, 80% of the present mortality caused by alcoholic psychosis, alcoholism, cirrhosis of the liver, or alcohol poisoning in Sweden occurs among men .
The aim of the present study was to analyse whether the risk of alcohol-related inpatient care and/or death differs between parents who adopt a gender-stereotypical division of parental duties in early parenthood and those who adopt a less gender-stereotypical position as indicated by paternity leave for fathers and full-time work for mothers. The concepts of 'alcohol consumption' and 'drinking' will consider both frequency and quantity, while 'risky consumption/drinking' will refer to frequencies or quantities that are likely to imply alcohol-related inpatient care and/or death in the future.
Our overall hypothesis is that gender equality, in terms of more or less similarity between women and men in all spheres of life , leads to a convergence in of alcohol consumption and its consequences [14, 29]. We anticipate that initial role expansion is associated with a decrease in risky drinking practices among both sexes, but also that the step from part-time to full-time work is linked with increased risky drinking in mothers. Besides, we acknowledge that childcare duties may per se protect against risky drinking. All in all, the theories of expansion, stress, and caring lead us to hypothesise a negative association between paternity leave and alcohol harm among men and a positive association between women's full-time work and alcohol harm. Finally, we recognise that the relationships could differ by age, occupational position, cohabitation status, whether the partner work full-time (in the male analysis), and whether the partner took parental leave (in the female analysis) [14, 24], although these potential effect modifications were assessed from an explorative perspective.