Henrik Brønnum-Hansen

Introduction to Danish (nationwide) registers on health and social issues: Structure, access, legislation, and archiving

Danish registers contain information on many important health and social issues. Because all Danish citizens have a unique personal identification number, linkage at the individual level between these nationwide registers and other data sources is possible and feasible. In this paper we briefly introduce selected Danish registers and the data structure and requirements for getting access to data at Statistics Denmark, which is the main provider of register data. We introduce the Danish Data Archive and briefly present the Act on Processing of Personal Data, which is the legal foundation for analyses of register-based data in Denmark.

Suicide and multiple sclerosis: an epidemiological investigation.

In a nationwide investigation the risk of death by suicide for patients with multiple sclerosis (MS) was assessed using records kept at the Danish Multiple Sclerosis Registry (DMSR) and the Danish National Register of Cause of Death. The investigation covers all MS patients registered with DSMR with an onset of the disease within the period 1953-85, or for whom MS was diagnosed in the same period. Fifty three of the 5525 cases in the onset cohort group committed suicide. Using the figures from the population death statistics by adjustment to number of subjects, duration of observation, sex, age, and calendar year at the start of observation, the expected number of suicides was calculated to be nearly 29. The cumulative lifetime risk of suicide from onset of MS, using an actuarial method of calculation, was 1.95%. The standard mortality ratio (SMR) of suicide in MS was 1.83. It was highest for males and for patients with onset of MS before the age of 30 years and those diagnosed before the age of 40. The SMR was highest within the first five years after diagnosis.

Danish EQ-5D population norms

Background: The EQ-5D is a widely used generic health-related quality of life instrument that has been used to describe population health and health outcomes in clinical trials and health economic evaluations. Aims: To generate Danish population norms for the EQ-5D index score, stratified by age and gender. Methods: The EQ-5D data from three population health surveys were pooled, thus providing EQ-5D profile data for 15,700 individuals aged 20-79 years. The Danish TTO scoring algorithm was used to weight each respondents profile data to derive a single index score. Mean values were computed by gender and 10-year age groups, and educational groups. Results: In a random sample from the general Danish population, the mean EQ-5D index score ranged between 0.93 for 20—29 year-olds and 0.83 for 70—79 year-olds. Men had a significantly higher score than women in all age groups. Longer education was associated with higher EQ-5D index score in most age groups. Conclusions: The calculated mean values for the EQ-5D index score may be used as reference values for comparative purposes in future Danish population health and evaluative studies.

Socioeconomic status and trends in risk factors for cardiovascular diseases in the Danish MONICA population, 1982–1992

STUDY OBJECTIVE The decline in cardiovascular mortality in Denmark during the 1980s has been greatest in the highest socioeconomic groups of the population. This study examines whether the increased social inequality in cardiovascular mortality has been accompanied by a different trend in cardiovascular risk factors in different educational groups. DESIGN Data from three cross sectional WHO MONICA surveys conducted in 1982–84, 1987, and 1991–92, were analysed to estimate trends in biological (weight, height, body mass index, blood pressure, and serum lipids) and behavioural (smoking, physical activity during leisure, and eating habits) risk factors in relation to educational status. SETTING County of Copenhagen, Denmark. PARTICIPANTS 6695 Danish men and women of ages 30, 40, 50, and 60 years. MAIN RESULTS The prevalence of smoking and heavy smoking decreased during the study but only in the most educated groups. In fact, the prevalence of heavy smoking increased in the least educated women. There was no significant interaction for the remaining biological and behavioural risk factors between time of examination and educational level, indicating that the trend was the same in the different educational groups. However, a summary index based on seven cardiovascular risk factors improved, and this development was only seen in the most educated men and women. CONCLUSION The difference between educational groups in prevalence of smoking increased during the 1980s, and this accounted for widening of an existing social difference in the total cardiovascular risk.

Underlying cause of death in Danish patients with multiple sclerosis: results from the Danish Multiple Sclerosis Registry

OBJECTIVES To determine the underlying causes of death in a large population based register series of patients with multiple sclerosis. METHODS The Danish Multiple Sclerosis Registry, which contains virtually all diagnosed cases of multiple sclerosis in Denmark who were alive in 1949 plus cases with onset of multiple sclerosis in the period 1949–93, who have been diagnosed and notified by 1 January 1994, was linked with the Danish Registry of Causes of Death, in which ICD codes for causes of death from the death certificate are stored for all Danish citizens. RESULTS 6068 register cases of multiple sclerosis, who had died in the period 1951–93, were included. Multiple sclerosis was noted on the death certificate as the underlying cause of death in 55.4%; cardiac or vascular diseases in 17.6%; cancers in 8.6%; respiratory or infectious diseases in 5.1%; other natural causes in 9.5%; accident or suicide in 3.8%. The distribution varied with age at death. Standardised mortality ratios (SMRs) were computed on the basis of the 8142 incident cases, who had onset of multiple sclerosis within the period 1951–93; the SMRs for causes of death other than multiple sclerosis were highest for infectious or pulmonary diseases: 2.46 (95% confidence interval (95% CI) 2.04–2.94); suicide: 1.62 (95% CI 1.29–2.01); cardiac or vascular diseases: 1.34 (95% CI 1.22–1.48); accidents 1.34 (95% CI 1.02–1.71); and significantly lower than unity for cancers: 0.79 (95% CI 0.70–0.90), lower for men than for women. CONCLUSIONS More than half of the patients with multiple sclerosis die from multiple sclerosis or complications of the disease. Among other causes, patients with multiple sclerosis have an increased risk of dying from heart or vascular diseases but a reduced risk of dying from cancer. An increased risk of death from suicide and accidents can be indirectly attributed to multiple sclerosis. The diminished risk of dying from cancer may be a result of incomplete ascertainment of cancers in disabled patients with multiple sclerosis.

Concordance for multiple sclerosis in Danish twins: an update of a nationwide study

The occurrence of multiple sclerosis (MS) in twins has not previously been studied in complete nationwide data sets. The existence of almost complete MS and twin registries in Denmark ensures that essentially unbiased samples of MS cases among twins can be obtained. In this population-based study, virtually all Danish MS cases among twins born before 1983 with onset of MS after 1948 and diagnosis before 1 January 1997 were identified. Of 13 286 MS cases, 178 were twins and, of these 164 twin pairs were discordant and seven were concordant. We found significantly higher proband-wise concordance among monozygotic twins than dizygotic twins, with estimated proband-wise concordances of 24% (95% confidence interval (CI): 5-39%) for monozygotic and 3% (95% CI: 0-8%) for dizygotic twins. Thus, a monozygotic twin whose co-twin has MS has a 24% risk of developing the disease, while the corresponding risk for a dizygotic twin is only 3%. Our results largely confirm previously published concordance estimates and indicate that genetic factors are of importance in susceptibility to MS.

Suicide among Danes with multiple sclerosis

Objective: To compare the suicide risk among Danish citizens with multiple sclerosis with that of the general population, and to evaluate changes over 45 years. Methods: The study was based on linkage of the Danish Multiple Sclerosis Registry to the Cause of Death Registry. It comprised all 10 174 persons in whom multiple sclerosis was diagnosed in the period 1953 to 1996. The end of follow up was 1 January 1999. Standardised mortality ratios (SMRs) were calculated for various times after diagnosis and for age and calendar period of diagnosis. Results: In all, 115 persons (63 men, 52 women) had taken their own lives, whereas the expected number of suicides was 54.2 (29.1 men, 25.1 women). Thus the suicide risk among persons with multiple sclerosis was more than twice that of the general population (SMR = 2.12). The increased risk was particularly high during the first year after diagnosis (SMR = 3.15). Conclusions: The risk of suicide in multiple sclerosis was almost twice as high as expected more than 20 years after diagnosis. The excess suicide risk has not declined since 1953.

Stable Stroke Occurrence Despite Incidence Reduction in an Aging Population Stroke Trends in the Danish Monitoring Trends and Determinants in Cardiovascular Disease (MONICA) Population

BACKGROUND AND PURPOSE A stroke register was established at the Glostrup Population Studies in 1982 with the objective to monitor stroke occurrence in the population continuously during a 10-year period and contribute data to the WHO Monitoring Trends and Determinants in Cardiovascular Disease (MONICA) Project. The purpose of the current analysis was to estimate temporal trends in stroke occurrence. METHODS All stroke events in the study population were ascertained and validated according to standardized criteria outlined by the WHO MONICA Project. The study population comprised all subjects > or = 25 years of age. Stroke was defined by the clinical presentation. A total of 5262 stroke events in >2 million person-years were analyzed. Age-adjusted rates for first-ever stroke and for all stroke events were calculated and temporal trends estimated by means of Poisson regression. RESULTS The overall annual stroke attack rate per 100,000 person-years in the age range > or = 25 years was 272 in men and 226 in women. Age-adjusted stroke attack rates decreased among men by 3.9% per year and by 4.1% among women. Age-adjusted stroke incidence rates declined by 2.9% in men and by 3. 1% in women. The trends were statistically significant in both sexes. However, the proportion of elderly people in the study population increased during the time period of the study. Hence the numbers of stroke victims in the population remained largely unaltered. CONCLUSIONS Decreasing age-adjusted stroke incidence rates point to a reduction of stroke risk during the time period of the study. Cardiovascular prevention, in particular improved hypertension control, is believed to have contributed to the incidence reduction. However, the burden of stroke on the healthcare system did not substantially diminish. The gain likely achieved from reduction of preventable risk factors was almost counterbalanced by population aging.

The risk of multiple sclerosis in bereaved parents A nationwide cohort study in Denmark

Background: Previous studies have suggested that psychological stress may play a role in the risk of multiple sclerosis (MS), but the evidence is very limited. Objective: To examine the association between MS and a well-defined major stressful life event: the death of a child. Methods: In this follow-up study based on nationwide and population-based registers, all 21,062 parents who lost a child younger than 18 years from 1980 to 1996 in Denmark were included in the exposed cohort and 293,745 matched parents who did not lose a child in the unexposed cohort. The two cohorts were followed for incident MS from 1980 to 1997. Hazard ratios (HR) with 95% CI were calculated as the measure of association between the exposure and MS, using the Cox proportional hazards regression model. Results: Two hundred fifty-eight MS patients were identified (28 in the exposed cohort and 230 in the unexposed cohort). The exposed parents had an increased risk of MS (HR 1.56, 95% CI 1.05 to 2.31), which is significant only when follow-up was at least 8 years. The HR for definite/probable MS was 1.42 (95% CI 0.90 to 2.24). Parents who lost a child unexpectedly had an HR of 2.13 (95% CI 1.13 to 4.03) for all MS, which is higher than that for other bereaved parents (HR 1.33; 95% CI 0.81 to 2.16). Conclusion: Psychological stress may play a role in the development of MS.

Mortality and causes of death in autism spectrum disorders An update

This study compared mortality among Danish citizens with autism spectrum disorders (ASDs) with that of the general population. A clinical cohort of 341 Danish individuals with variants of ASD, previously followed over the period 1960—93, now on average 43 years of age, were updated with respect to mortality and causes of death. Standardized mortality ratios (SMRs) were calculated for various times after diagnosis. In all, 26 persons with ASD had died, whereas the expected number of deaths was 13.5. Thus the mortality risk among those with ASD was nearly twice that of the general population. The SMR was particularly high in females. The excess mortality risk has remained unchanged since our first study in 1993. Eight of the 26 deaths were associated with epilepsy and four died from epilepsy. Future staff education should focus on better managing of the complex relationships between ASD and physical illness to prevent avoidable deaths.