April 8, 2014. About one-third of people in Denmark seek treatment for a mental disorder at some point during their lives, according to a study published online March 26 in JAMA Psychiatry. The new study offers one of the most comprehensive looks at treated mental disorders, including substance abuse, schizophrenia, mood disorders, eating disorders, intellectual disability, and autism, as well as dementia related to diseases such as Alzheimer's.
Carsten Bøcker Pedersen and colleagues at Aarhus University in Denmark along with other researchers around the world surveyed Danish health registry records to find people who received their first treatment for a mental disorder between 2000 and 2012. The study also tracked how incidence changes over a lifetime, rather than focusing on a limited age group. These distinctive “signatures” of incidence show how different stages of life are beset by different vulnerabilities, something that may help identify root causes of mental disorders and also inform healthcare policies.
Across many disorders, the number of new cases showed a sharp rise in early adulthood. For some such as mood disorders or substance abuse, a second rise emerged later in life. For schizophrenia, incidence peaked in early adulthood, during which men had a higher incidence than women.
Although finding out how common an illness is may seem like a simple enough counting exercise, this process is fraught with trade-offs. Previous studies have taken a population-based survey approach to sampling, in which researchers go out into the community to find people with mental disorders (e.g., Kessler et al., 1994). Though this approach can detect some of those not receiving treatment, it misses others, such as people living in institutions or those who moved or died before being contacted—all strong possibilities for those with mental illness.
The new study turns to a centralized database maintained in Denmark that contains data on all inpatient and outpatient visits for psychiatric reasons. Though this database only considers information on those who seek treatment for a mental disorder, it is considered a representative sample from the 5.6 million residents of Denmark, where free healthcare is provided by the government. Other previous registry-based studies have focused on a single disorder (e.g., Thorup et al., 2007), but the new study grapples with a broad range of them.
First author Pedersen and colleagues found that 320,543 people received their first treatment for any mental disorder between 2000 and 2012. The researchers focused on incidence—the number of new cases—to capture information about disease onset across the human lifespan, which could shed light on causes. Nearly half of the first treatment visits were related to anxiety disorders, with smaller yet sizeable proportions related to mood disorders, dementia, and substance abuse.
Breaking the numbers down by age revealed the rise and fall of the number of new cases over a lifetime, with each disorder displaying its own signature shape. For example, dementia-associated illnesses rose abruptly at 70 years of age, whereas intellectual disability and other developmental disorders such as autism peaked in the first decade of life. Mood disorders showed two peaks, with incidence hitting a high point in early adulthood, then surging again late in life. Such bimodal shapes within these signatures not only indicate different windows of vulnerability, but also suggest different causes.
Though 32.05 percent of men and 37.66 percent of women received treatment for any mental disorder, they diverged in their specific patterns. For eating disorders, women were by far the ones seeking help during the second and third decades of life, amounting to 3 percent of women in the population compared to 0.17 percent of men. Substance abuse achieved its highest incidence at about 20 years of age for both males and females; however, in their forties and fifties, women but not men showed a secondary peak in incidence.
The bimodal pattern for mood disorders was more pronounced in women, who outpaced men in incidence at nearly every point in life (lifetime risk of 9.95 percent for men and 16.48 percent for women). This skewing stemmed mainly from cases of major depressive disorder (9.07 percent men, 15.50 percent women) rather than bipolar disorder (1.32 percent men, 1.84 percent women).
For schizophrenia, men and women showed a similar lifetime risk (1.93 percent for men, 1.56 percent for women) and somewhat similar time-varying signatures. Incidence peaked for both sexes at approximately 20 years of age, though this peak was slightly lower and trailed off more quickly with age for women than for men. When the researchers broadened the diagnosis to include other schizophrenia-related disorders (e.g., schizoaffective disorder), they found that females had a slightly higher incidence rate than males did after 50 years of age.
The researchers suggest that, because their numbers are based on treated cases only, they likely underestimate the toll of mental disorders in Denmark. Despite this, the numbers argue that the risk for mental disorders does not go away as we age, and highlight a need for sizeable mental health resources geared toward all stages of life.—Michele Solis.
Pedersen CB, Mors O, Bertelsen A, Waltoft BL, Agerbo E, McGrath JJ, Mortensen PB, Eaton WW. A comprehensive nationwide study of the incidence rate and lifetime risk for treated mental disorders. JAMA Psych. 2014 Mar 26. Abstract