New insights into mental illness and physical comorbidity

Is there a link between mental illness and cancer, and if so, which comes first?

The physical health needs of people with a psychiatric disorder are nearly three times higher than for people without a psychiatric disorder

An analysis of physician billing records for nearly 700,000 individuals in Canada from 1994 to 2009 revealed a cumulative rate of psychiatric disorder of 53% over 16 years, said Professor David Cawthorpe, Calgary, Canada. And the physical health needs for these individuals was nearly three times higher than for people without a psychiatric disorder.¹

People with a psychiatric disorder therefore have greater morbidity, but which comes first? The psychiatric disorder or the physical morbidity? asked Professor Cawthorpe.

Which comes first — psychiatric disorder or the physical morbidity?

To investigate the temporal relationship between psychiatric disorder and physical morbidity, Professor Cawthorpe and his colleagues analyzed approximately 75 million physician billing records between 1993 and 2010 using the following strategies:²

• First, using any cancer as the index diagnosis and pivot, with all mental disorders before and after the cancer
• Then, using any mental disorder as an index diagnosis and pivot, with all cancers before and after the mental disorder

Mental disorders are more likely to precede cancer

People were more likely to have both mental disorder and cancer, compared to either one or neither.²

It was more likely that any cancer would follow any mental disorder, said Professor Cawthorpe, with odds ratios (OR) (95% confidence intervals [CI]) as follows:

• For females, 1.96 (1.92, 2) for those aged 19–49 years, and 1.49 (1.44, 1.55) for those aged ≥50 years
• For males, 1.53(1.5, 1.57) for those aged 19–49 years, and 1.46 (1.41, 1.52) for those aged ≥50 years²

What is the average duration of a psychiatric disorder before the development of cancer?

Psychiatric disorder may precede cancer by 4 years

The average duration of a psychiatric disorder before the development of cancer and the proportions of male and female populations affected across four independent groups of psychiatric disorders — affective psychoses, schizophrenic disorders, depressive disorders and neurotic disorder — were evaluated, said Professor Cawthorpe.

The results revealed consistent proportions of males and females (between 60 and 69%) with an average preceding duration of approximately 4 years across the four groups of psychiatric disorders.² 

Neurosis or depression may precede ulcerative colitis by an average of 5 years

These findings — the temporal relationship and duration of a mental disorder before the development of cancer — are consistent with the temporal relationship and duration of a mental disorder before the development of ulcerative colitis revealed by a previous study carried out by Professor Cawthorpe and his colleagues.³

Neurosis or depression preceded ulcerative colitis by an average of 5 years, but there was no difference for the other psychiatric disorders,³ said Professor Cawthorpe.

Physical diseases among patients and siblings with bipolar disorder

A nationwide population-based longitudinal study mapping physical diseases in patients with bipolar disorder and their siblings was presented by Professor Lars Vedel Kessing, Copenhagen, Denmark.

Bipolar disorder is associated with increased rates of any disorder likely to involve an inflammatory pathogenesis

Approximately 20,000 patients with bipolar disorder and approximately 14,000 unaffected siblings, and 20 controls were followed up for 23 years from 1995 until 2017.⁴

Professor Kessing highlighted that bipolar disorder was associated with increased rates of:

• All physical disease categories compared with rates for control individuals, except for cancer
• Disorders likely to involve an inflammatory pathogenesis, including ischemic heart disease, diabetes, dementia, hypertension, hypercholesterolemia and hyperlipidemia, hypothyroidism and infections⁴

The excess of physical diseases among patients with bipolar disorder is not familial

In contrast, siblings unaffected by bipolar disorder had increased rates of certain infectious and parasitic diseases, and diseases of the nervous system, digestive system, and genitourinary system.⁴ The excess of physical diseases among patients with bipolar disorder is therefore not familial, concluded Professor Kessing.