Co-occurrence between mental disorders and physical diseases: a study of nationwide primary-care medical records

Abstract

Background: Mental disorders and physical-health conditions frequently co-occur, impacting treatment outcomes. While most prior research has focused on single pairs of mental disorders and physical-health conditions, this study explores broader associations between multiple mental disorders and physical-health conditions.

Methods: Using the Norwegian primary-care register, this population-based cohort study encompassed all 2 203 553 patients born in Norway from January 1945 through December 1984, who were full-time residents from January 2006 until December 2019 (14 years; 363 million person-months). Associations between seven mental disorders (sleep disturbance, anxiety, depression, acute stress reaction, substance-use disorders, phobia/compulsive disorder, psychosis) and 16 physical-health conditions were examined, diagnosed according to the International Classification of Primary Care.

Results: Of 112 mental-disorder/physical-health condition pairs, 96% of associations yielded positive and significant ORs, averaging 1.41 and ranging from 1.05 (99.99% CI 1.00-1.09) to 2.38 (99.99% CI 2.30-2.46). Across 14 years, every mental disorder was associated with multiple different physical-health conditions. Across 363 million person-months, having any mental disorder was associated with increased subsequent risk of all physical-health conditions (HRs:1.40 [99.99% CI 1.35-1.45] to 2.85 [99.99% CI 2.81-2.89]) and vice versa (HRs:1.56 [99.99% CI 1.54-1.59] to 3.56 [99.99% CI 3.54-3.58]). Associations were observed in both sexes, across age groups, and among patients with and without university education.

Conclusions: The breadth of associations between virtually every mental disorder and physical-health condition among patients treated in primary care underscores a need for integrated mental and physical healthcare policy and practice. This remarkable breadth also calls for research into etiological factors and underlying mechanisms that can explain it.

Keywords: comorbidity; health registry data; integrated healthcare; mental disorders; mental physical comorbidity; nationwide cohort; physical-health conditions; primary care.

Figure 1.

Associations between any mental disorder and 16 physical-health conditions in primary-care practices across 14 years. Panel A shows associations (odds ratios and 99.99% confidence intervals) between any mental-disorder diagnosis (a binary variable) and 16 physical-health conditions. The figure is organized from the weakest (left and bottom) to the strongest (right and top) associations. Panel B shows the risk of 16 physical-health conditions among patients who did and did not present with any mental disorder. Inverse probability weighting was used to balance on four demographic variables: age at baseline, sex assigned at birth, educational attainment, and county of residence. Results for specific mental disorders are shown in online Supplementary Figs S1–S7. (A) Associations between any mental disorder and 16 physical-health conditions. (B) Risk of 16 physical-health conditions for patients with and without any mental disorder.

Figure 2.

Associations between mental disorders and physical-health conditions. Panel A shows a heatmap of associations (odds ratios) between seven specific mental disorders and 16 physical-health conditions across a 14-year period in primary-care patients. The figure is organized from the strongest (top) to the weakest (bottom) associations with any mental health disorder. Inverse probability weighting was used to balance on four demographic variables: age at baseline, sex assigned at birth, educational attainment, and county of residence. The odds ratios shaded in grey are not statistically significant (i.e. the 99.99% confidence interval includes 1.0). All other odds ratios were statistically significant (i.e. 99.99% confidence interval does not include 1.0.). Panels B and C show multimorbidity associations between variety of different mental health disorders and variety of different multiple physical health conditions. Exact percentages are shown in online Supplementary Tables S7–S8. Inverse probability weighting was used to balance on four demographic variables: age at baseline, sex assigned at birth, educational attainment, and county of residence. (A) Heatmap of associations (odds ratios) between seven specific mental disorders and 16 physical-health conditions across a 14-year period in primary-care patients. (B) Multimorbidity associations between variety of different physical health conditions and variety of different mental health disorders. (C) Multimorbidity associations between variety of different mental health disorders and variety of different multiple physical health conditions. MH, mental health; PH, physical health.

Figure 3.

Bidirectional associations between any mental disorder and 16 physical-health conditions among primary-care patients across a 14-year observation period. Panel A shows the risk (hazard ratios) of 16 physical health conditions after a diagnosis of any mental health disorder and panel B shows the risk (hazard ratios) of any mental disorder after a diagnosis of 16 physical-health conditions. Inverse probability weights were used to balance on four demographic variables: sex, age, educational attainment, and county of residence. Within each month from January 2006 through December 2019, encounters with primary-care providers were assessed for mental health disorders and physical health conditions. Extended Cox proportional hazards models were used, treating dependent time-to-event variables and independent exposures as recurrent and time-varying, respectively. Results for specific mental disorders are shown in online Supplementary Figs S14–S15. (A) Risk of 16 physical-health conditions after any mental disorder. (B) Risk of any mental disorder after 16 physical-health conditions.

Figure 4.

Evaluating surveillance bias in the association between any mental disorder and 16 physical-health conditions among primary-care patients. Panel A shows the distribution of time from first observed diagnosis of any mental disorder to first subsequent diagnosis of 16 physical-health conditions over the 14-year period. Panel B shows the distribution of time from first observed diagnosis of 16 physical-health conditions to first subsequent diagnosis of any mental disorder over the 14-year period. Exact percentages are shown in online Supplementary Tables S9–S10. (A) Timing of 16 physical-health conditions after any mental disorder. (B) Timing of any mental disorder after 16 physical-health conditions.