Alcohol-related disorders among elite male soccer players in Sweden: nationwide cohort study
Data sources
Detailed information about the data sources and the methods used to construct the study cohort can be found in the supplementary material. Information about soccer players has been collected from data sources for all current and former soccer players in Sweden’s highest competition, the Allsvenskan, and has been compiled by Sweden’s association of soccer historians and statisticians. This information included full name, date of birth, seasons and number of matches played, number of goals scored, team represented and player position (outside or goalkeeper). In databases run by the Swedish Tax Agency and the National Association of Genealogists, name and date of birth were used to search for the player’s social security number, a number given to all residents of Sweden that enables linking of data at the individual level across data sources (supplementary material and supplementary table 1). We used several nationwide health and administrative registers, including the Total Population Register (vital status, region of residence, region of birth), Patient Register (outcome), Cause of Death Register (outcome), Medicines Register (outcome), Statistics Norway. (income, education), and the Swedish military conscription register (results from psychological and physical tests during military conscription).
Study population
A flowchart for the study population is shown in supplementary figure 1. All soccer players who had played at least one match in the Allsvenskan from their first season in 1924 to 2019 were included. We excluded players whose social security number was not available in the databases (e.g. because players removed themselves from public databases, had died before the introduction of identity numbers, or were foreign players without an identity number). We also excluded players for whom a social security number could not be identified because several people had the same name and date of birth, and it was not possible to identify the football player among them. We excluded players who were not registered in the Total Population Register, which started in 1969.
Each footballer was matched in a 1:10 ratio with men from the general population, based on year of birth, region of residence and vital status, to form a base cohort. The matching variables had no missing data. The matching date was January 1 of the year in which the footballer played his first match in the Allsvenskan or was first registered as a resident of Sweden (if this occurred after the first year of playing in the Allsvenskan), and the matching was carried out using the Total Population Register. For players who played their first season before 1969 (ie, the start of the general population registry), we selected men from the general population matched by vital status and region of residence on January 1, 1969. The date on which players and men from the general population were matched constituted cohort entry.
From the base cohort, we excluded players (and matched men from the general population) and men from the general population who were not born in Sweden and who had their first stay in the country after the age of 15. We used this exclusion criterion because foreign players are likely to emigrate during or shortly after their football career, which would preclude long-term follow-up.
Results
The primary outcome was alcohol-related disorders recorded in the Cause of Death Registry (primary or contributing causes of death), the National Patient Registry (primary or secondary diagnosis during hospital or outpatient visits) or the Prescription Drug Registry (filled prescriptions for drugs used to treat alcoholism). The secondary outcome was disorders related to the abuse of other drugs. The ICD-8, ICD-9, ICD-10 (International Classification of Diseases, 8th–10th Revisions) and Anatomical Therapeutic Chemical codes used to define the outcomes are shown in Supplementary Table 2.
Statistical analysis
Football players and men from the general population were followed from cohort entry until emigration, outcome event, death or end of follow-up (December 31, 2020). Emigration, death that did not include an outcome event, and end of follow-up constituted censoring events. We used Cox regression analysis with age as the time scale and adjusted for residential area, place of birth and calendar time as a time-varying covariate (Supplementary Table 3) to estimate the hazard ratio for the primary outcome among soccer players versus men from the general population.
We performed further analyses. Rules and norms for alcohol consumption among soccer players have differed significantly over time in Sweden.1819 We therefore modeled the interaction between the year of the player’s first season in the top tier of competitions using restricted cubic splines with 3 knots and a flexible parametric survival model20 to calculate the hazard ratio for soccer players versus matched men from the general population by year of the soccer player’s first season.
Some of the most high-profile cases of alcohol addiction have occurred among players known for their goal-scoring abilities. Previous studies have shown associations between personality traits and alcohol consumption.21 Therefore, we hypothesized that factors potentially associated with goal-setting (eg, sensation seeking),21 may also be associated with the risk of alcohol-related disorders. Furthermore, footballers who have played many games and seasons in the top tier could have been more exposed to drinking culture associated with elite football, fame and public scrutiny. Another possibility is that football players with alcohol problems could have ended their careers early. We therefore hypothesized that the number of matches and seasons in the top tier may be associated with alcohol-related disorders.
In analyzes restricted to soccer players, we used the Cox regression model additionally adjusted for birth cohort (categorical variable; Supplementary Table 3) to separately assess the association with alcohol-related disorders for number of goals scored per 10 matches (among outfield players who had played at least 10 matches), the number top tier matches played and the number of seasons played, modeled with 3-knot cubic splines. We also assessed the risk of alcohol-related disorders among outfielders versus goalkeepers.
Studies have shown that elite athletes may be at increased risk for alcohol-related disorders after they retire from their elite careers141522 due to changes in life circumstances associated with retirement. We therefore assessed whether the risk of alcohol-related disorders among soccer players versus men from the general population varied across age. Because outcome data from death certificates and hospitalizations may poorly reflect the time of first diagnosis, we set the earliest cohort entry to January 1, 2002, one year after the start of nationwide coverage for outpatient visits in the National Patient Registry. We excluded footballers (and matched men from the general population) and men from the general population who had died, emigrated or had any history of alcohol-related disorders before cohort entry. We calculated the hazard ratio for the risk of alcohol-related disorders for soccer players versus men from the general population using total follow-up time in this analysis, and in another analysis modeled age with restricted cubic splines with 3 knots.
We performed a sensitivity analysis. The earliest possible cohort entry was 1969. If gamblers and men from the general population had different risks of dying from alcohol-related disorders, the exclusion of those who died before 1969 could lead to left truncation bias due to a depletion of individuals susceptible to alcohol-related disorders diseases disorders.23 We therefore conducted an analysis that included only those players and those men from the general population who were 49 years of age or younger at cohort entry.
We conducted exploratory analyzes to assess the effect of accounting for certain characteristics that may differ between elite soccer players and men from the general population. Some men from the general population could have had serious health or social problems that precluded participation in the labor force and increased the risk of alcohol-related disorders. Therefore, we performed two analyzes excluding men from the general population with zero recorded income at cohort entry and at age 40–44 years (Supplementary Table 4). For these analyses, we excluded men from the general population without available income data and football players without matched men from the general population for whom income data were available. We then performed the analysis with and without the exclusion of men from the general population with zero registered income.
Next, we used data from the military conscription register. First, we performed the analysis with all soccer players and men from the general population born 1951-87, since military conscription was mandatory at about age 18 for men born during this period.24 Individuals living abroad, those with certain health conditions, and those with disabilities were exempt from conscription or testing (Supplementary Material (Data Sources) and Supplementary Table 4), so we did the analyzes excluding football players and men from the general population born 1951-87 without complete data on test results, e.g. stress dependence, cognitive ability, body mass index, muscle strength and cardiorespiratory exercise capacity (Supplementary Table 4). We then performed analyzes adjusting for stress resilience and cognitive ability scores.252627 Finally, we further adjusted the model for body mass index, muscle strength, and cardiorespiratory exercise capacity.
The secondary outcome of disorders related to other substance abuse was also assessed. ICD-8 codes, used before 1987, did not include diagnoses suitable for capturing the secondary outcome on death certificates, so we set the earliest date of cohort entry to January 1, 1987, when nationwide coverage in the National Patient Registry for inpatient diagnoses began. In these analyses, we excluded players who died or emigrated before 1987 and their matched general population males and general population males who died or emigrated before 1987. We also excluded players and general population males aged 65 years or older in 1987 to avoid potential left truncation bias.23
Analyzes were performed using SAS software (version 9.4) and Stata (version 16.1). Hazard ratios whose confidence intervals did not overlap 1.0 were considered significant.