Data sources

We obtained information on mental health, general health, alcohol risk behaviour and smoking status from the health check survey, which participants were requested to complete electronically before attending the clinical examination. Survey data and clinical data from Check Your Health were linked to data in the Danish registers through each individual’s unique personal identification number, which is assigned to all individuals with permanent residence in Denmark.²⁸

The mental health status was assessed at the screening by the mental component summary (MCS) score, which is part of the 12-item Short-Form Health Survey (SF-12) V.2.²⁹ The SF-12 is a condensed and validated version of the SF-36, which is an acknowledged and widely used multifactorial measure of generic health-related quality of life in the general population.^30–32 The SF-12 has been validated in the population of the Central Denmark Region,³¹ where Randers Municipality is located, and the SF-12 is used in Danish national and regional health surveys. The MCS score provides a generic measure of mental health status based on general self-rated health, mood and anxiety symptoms, and functional limitations during the past 4 weeks.²⁹ The MCS score has been suggested useful for screening for common mental disorders.³³ An MCS score of <36 has been shown to have a sensitivity of 0.62 for any depressive disorder and of 0.73 for generalised anxiety disorder in a general population aged 32–58 years.³⁴ Thus, the MCS measures more than just mental disorders and is considered a valid measure of mental health status in population studies.^{30 32} The calculation of MCS scores was based on 1998 general US population norms and was performed only for complete SF-12 data.³⁰ MCS scores range from 0 to 100 on a continuous scale, and a higher score reflects better mental health.

Poor mental health was defined as an MCS score of ≤35.76 based on a Danish national health survey, where poor mental health corresponded to the 10% of the Danish adult population with the lowest MCS scores.³⁵

A total of 98% of the population in Denmark are listed with a GP.³⁶ Mental healthcare is generally free of charge for the patient, except for psychological therapy and pharmaceuticals, which both require an out-of-pocket fee. The public healthcare system covers mental health services from the GP (psychometric testing and talk therapy), 60% of the psychologist fee for patients who fulfil certain referral criteria and partial payment for prescription medication. If referred by the GP, patients can also get psychiatric specialist care free of charge.

‘Mental healthcare’ was defined as at least one of the following types of intervention recorded in the Danish national health registers: psychometric testing by GP (Danish National Health Service Register (NHSR)³⁷), talk therapy by GP (NHSR), contact with a psychologist (NHSR), contact with a psychiatrist (NHSR and Danish National Patient Register)³⁸ or redemption of psychotropic medication (Danish National Prescription Register)³⁹ (table 2).

Types of health services and treatments included in the definition of ‘mental healthcare’

ATC, Anatomical Therapeutic Chemical Classification; DNPR, Danish National Prescription Register; GP, general practitioner; NHSR, Danish National Health Service Register; NPR, Danish National Patient Register.

‘Initiation of mental healthcare’ was defined as initiation of any type of mental healthcare registered within 1 year after the date of the mental health screening.

Clinical measures were obtained by trained healthcare staff using standardised methods, for example, height measured with heels touching the wall at deep inspiration; and mean systolic and diastolic blood pressure calculated from three measures on the left arm with 1 min intervals after 5 min rest.²⁷ Blood pressure was measured with Omron M6 (Omron Healthcare Europe). Cholesterol and low-density lipoprotein were measured by finger blood test with Alere Cholestech LDX System (Alere Denmark). Glycated haemoglobin was measured by finger blood test with DCA Vantage Analyzer (Siemens Healthcare, Siemens, Germany). Ten-year risk of fatal cardiovascular disease was calculated with the Systematic Coronary Risk Evaluation European Low Risk Chart based on sex, age, systolic blood pressure, total cholesterol and smoking status and was extrapolated to age 60 years.⁴⁰ Lung function (forced expiratory volume in 1 s and forced vital capacity) was measured with the EasyOne Diagnostic Spirometer (ndd Medical Technologies, Andover, Massachusetts, USA).

From April 2012 to July 2013, we calculated alcohol risk behaviour using the four-item Cut down, Annoyed, Guilty, Eye-opener (Copenhagen) questionnaire.⁴¹ From August 2013, the Alcohol Use Disorders Identification Test (AUDIT)⁴² was used because AUDIT was implemented in the national guidelines to GPs. We dichotomised self-rated general health (SF-12 item 1)²⁹ into poor/fair and good (good, very good or excellent).

The Check Your Health steering committee (including GPs) decided that poor mental health or any of the other red flags listed in table 1 should prompt a recommendation for a follow-up consultation with the GP.²⁷

We obtained all sociodemographic variables within the year before invitation from administrative national registers managed by Statistics Denmark.⁴³ The sociodemographic explanatory variables used were sex, age, ethnicity, education, employment, cohabitation status and income as these were the most frequently examined variables in studies of healthcare utilisation.⁴⁴ We grouped country of origin into Western or non-Western. We categorised educational level into ≤10, 11–15 and >15 years of education according to the International Standard Classification of Education by UNESCO.⁴⁵ We grouped occupational status into employed, unemployed/benefits (unemployed at least half of the year or receiving sickness/parental benefit) or social welfare (early disability pension or social security benefits). We dichotomised cohabitation into cohabiting (married or living with a partner) or living alone (including widows and divorced). We calculated equivalence-weighted household income as recommended by the Organisation for Economic Co-operation and Development,⁴⁶ and we categorised income into tertiles. We gained information on vital status from the Danish Register of Causes of Death⁴⁷ and information on emigration from the Danish Civil Registration System.²⁸