Forty-five-year mortality rate as a function of the number and type of psychiatric diagnoses found in a large Danish birth cohort

People with psychiatric illness are known to be at a greater risk for premature death than those in the general, nonpsychiatric population.1–6 Life expectancy estimates may be reduced by as much as 20 years, depending on the primary psychiatric illness.7 Patients treated in a psychiatric inpatient unit are especially vulnerable to this effect, showing 2 to 3 times the rate of early mortality, compared with nonpsychiatric groups.2,7–9 Overall, standard mortality rates (SMRs) for psychiatric patients range from 1.7 to 3.0, indicating that premature death is 2 to 3 times more likely among psychiatric patients.2,8 These rates appear to be stable across different cultures and countries.1,2,10 Mortality rates reported in the past for psychiatric patients depend on numerous factors that include the administrative status of inpatients and outpatients, and the length of follow-up after discharge from treatment.8–11 Most prominently, the risk for early mortality among psychiatric inpatients is known to vary according to the age of the group studied and the type of psychiatric illness. Chronic and severe psychiatric illnesses, such as schizophrenia, alcoholism, and drug addiction, have consistently been associated with the higher early mortality rates.12,13 The availability of more effective pharmacological interventions, such as antipsychotics for patients with schizophrenia and antidepressants to treat depression, have been associated with a slight reduction of early mortality, but these rates remain high. Chwastiak et al12 have suggested that the increased risk of early mortality among psychiatric populations may be attributed to an increased level of comorbid nonpsychiatric medical conditions found among patients hospitalized on inpatient psychiatric units. Several studies have examined the relation between medical comorbidities in patients with a psychiatric diagnosis and the rate of early mortality. Psychiatric patients with multiple medical comorbid conditions were found to be at higher risk of early mortality than those without co-occurring medical conditions.14 These results reflect the Berkson Paradox or bias toward admissions and diagnosis of psychiatric illness preferentially in psychiatric patients with medical illness. Martin et al1 also observed that patient referrals to psychiatric outpatient clinics are often initiated by a comorbid medical condition, and that this relation was associated with an early mortality. Very little is known about the effect of psychiatric comorbidity on early mortality among patients with a psychiatric diagnosis, even though it is widely accepted that increasing numbers of co-occurring psychiatric syndromes are associated with poorer mental health outcomes. Previous studies have typically focused on the death rates of patients with a particular psychiatric diagnosis, compared with nonpsychiatric contrast groups. Less frequently, studies have compared the early mortality of patients with 2 different psychiatric illnesses in head-to-head examinations. We know of no other study examining the comparative mortality of a large group of people with psychiatric illness, where the full range of psychiatric diagnoses is available during a period of decades. In this investigation, we were fortunate to have access to information during 45 years on people who were part of a large birth cohort, born within 3 years of each other, and raised in the culturally and ethnically homogenous community of Copenhagen, Denmark. Moreover, because universal health care in Denmark extends back to the early 1900s,15 most people in Denmark who require psychiatric residential care receive this care in a government-operated facility, where the standards of diagnosis made by physicians were relatively uniform. Denmark has developed and maintained a computerized national register of patients’ psychiatric diagnoses since April 1, 1969,16 when the subjects of this birth cohort were aged about 9 years. The similarity of age, ethnic, and cultural influences as well as the standards used to characterize psychiatric illness in this large sample of hospitalized people with mental illness permits us to determine whether the number of different comorbid psychiatric diagnoses assigned to patients was predictive of premature death in men and women. The relatively large sample size of this cohort permitted a systematic examination of how certain diagnoses, independent of, and in combination with, other psychiatric diagnoses, were differentially associated with a higher likelihood of dying prematurely, both for men and for women, who are very similar in other respects.