A life course perspective on health in childhood and adulthood with special focus on health effects of smoking

Abstract: Abstract: The complexity of health relates to the interplay between numerous factors, e.g., biological and genetic factors, sociodemographic factors, life-style, environmental factors as well as health care services, all possibly acting throughout the life-course. While earlier health theories mainly have focused on adult life style as causes of adult ill-health, life-course research has in recent years emerged focusing also on earlier life experiences aiming to understand the biological, behavioural and psychosocial factors shaping the development of health and ill-health throughout the life-course and across generations. Smoking is a factor influencing the onset and development of poor health in all stages of life, with far-reaching health consequences for the unborn child as well as for the full grown adult. Smoking has been causally associated with both short and long-term adverse health effects, but has less often been investigated from a life-course perspective and especially not so among children and adolescents. Furthermore, the knowledge on the association between socioeconomic position and health has in recent years expanded through a broad life-course approach using different conceptual models. In this thesis, health in childhood and adulthood was investigated from a life-course perspective focusing on health effects of smoking. Paper one investigated the association between exposure to secondhand tobacco smoke at an early age and presence of allergic disease in 4 year old children in Malmö, Sweden (n=4278). Paper two investigated the long-term associations between smoking habits, environmental tobacco smoke exposure and progression of carotid intima-media thickening (IMT) and change in lumen diameter reduction due to plaque protrusion in various segments of the carotid artery (n=2992). Paper three investigated self-rated health (SRH) among second grade high school students related to age at smoking initiation (<14 years of age and ≥14 years of age) among current and former smokers, compared to never smokers. Furthermore, in paper four, socioeconomic differences in adult self-rated health was investigated using three socioeconomic life-course models, i.e., critical periods, accumulation of risk and social mobility models, using the participants in the 2008 public health survey in Skåne (n=28198) as the study population. Three out of the four studies were cross-sectional, but with retrospective information on smoking exposure, initiation of smoking and socioeconomic circumstances, respectively. The results showed that children exposed to secondhand tobacco smoke early in life had increased odds of allergic disease later in childhood if at least one parent had an allergic disease (Paper I). Furthermore, progression of IMT and rate of lumen diameter reduction due to carotid plaque protrusion was shown to increase from never smokers through former, moderate and heavy smokers, even after adjustment for traditional risk factors (Paper II). In second grade high school students, early smoking initiation was shown to be associated with poor self-rated health both among current and former smokers (Paper III). Regarding socioeconomic differences in adult self-rated health, the results in Paper IV showed a graded association between the combined effect of childhood and adulthood economic stress and poor SRH in accordance with the accumulation hypothesis. Furthermore, upward social mobility showed a protecting effect, while downward mobility increased odds ratios of poor SRH. The critical period hypothesis was confirmed in the sense that both economic stress in childhood and adulthood had independent effects on poor adult self-rated health. However, it was not confirmed in the sense that a particular window in time had a specifically high impact on self-rated health. In conclusion, the results from this thesis emphasise that health at a certain age is affected by current exposure e.g., life-style, sociodemographic and psychosocial factors, but, that also previous exposures are of importance. Future research should continue the difficult work with establishing causal links and temporal directions between exposure and health over the life-course. The collection of data from various periods in life allows the identification of effects of exposure during specific time periods on a specific outcome. Such knowledge may in turn be used in prevention and intervention. Future prospective cohort studies from early life, may contribute to such increased knowledge of lifelong health determinants, through more detailed assessments of exposure during different stages in life. The results from the thesis further emphasise the need for a continued work to prevent and decrease smoking.