Multimorbidity and health related quality of life in midlife – a longitudinal study from Northern Finland Birth Cohort 1966

Multimorbidity is a major public health concern. According to previous studies, multimorbidity has been shown to be associated with health-related quality of life (HRQoL). However, existing data concerning high income countries are mainly based on cross-sectional studies. Consequently, longitudinal investigations have been called for. There exist several definitions of multimorbidity in previous population studies, and usually definition is based on self-reported symptoms or diseases or included only few diagnoses. This study aimed to examine how the number of doctor-diagnosed chronic diseases influences HRQoL over time in a population-based setting. At 31 and 46 years, participants (<i>n</i> = 3573) of the Northern Finland Birth Cohort 1966 answered 15-Dimensional HRQoL questionnaire (15D). Mean 15D-Scores (varies between 0 and 1) were counted according to the number of 43 chosen chronic diseases. These diseases were found and the definition of multimorbidity was measured by a method using both self-reported doctor-diagnosed and register-based chronic diseases. In both genders, the mean difference of 15D-Scores increased monotonously in line with the increasing number of new emerging diseases diagnosed for 15 years of follow-up from the age of 31–46 years (<i>p</i> &lt; .05). Furthermore, the more diseases the patient had at the age of 31, the more mean 15D-Scores decreased when having more new emerging diseases at the age of 46. In general, HRQoL decreased during 15-year follow-up for everyone. Furthermore, decrease in the quality of life is significantly associated with multimorbidity in this longitudinal setting.