Low-level cognitive ability in young adulthood and other risk factors of depression in an observational cohort study among deployed Danish soldiers.

PURPOSE: Evidence exists of an association between pre-morbid lower cognitive ability and higher risk of hospitalization for depressive disorder in civilian cohorts. The purpose of this study was to examine the relationship of cognitive ability at conscription with post-deployment depression and the influence of (1) baseline factors: age, gender, and pre-deployment educational level, (2) deployment-related factors: e.g., war-zone stress and social support, and (3) co-morbid PTSD. METHODS: An observational cohort study linking conscription board registry data with post-deployment self-report data. The study population consisted of Danish Army military personnel deployed to different war zones from 1997 to 2015. The association between cognitive ability at conscription and post-deployment depression was analyzed using repeated-measure logistic regression models. RESULTS: Study population totaled 9716 with a total of 13,371 deployments. Low-level cognitive ability at conscription was found to be weakly associated with post-deployment probable depression after adjustment for more important risk factors like gender, education, and deployment-related factors [odds ratio (OR) 0.93, 95% confidence interval (CI) 0.88-0.99]. The co-occurrence rate with PTSD was nearly 60%. When adding co-morbid PTSD as an independent variable, the association between cognitive ability and probable depression became insignificant, OR 0.95, CI 0.89-1.02. CONCLUSIONS: Low cognitive ability at conscription is a risk factor for depression among returning military personnel, but unimportant compared to gender, education, and deployment-related factors. Part of this effect may be related to co-morbid PTSD. Use of cognitive ability score as an isolated selection tool cannot be recommended because of low predictive performance.

Hearing loss, cognitive ability, and dementia in men age 19-78 years.

Hearing loss in later life has been associated with risk of dementia. The impact of risk factors for dementia may change during life, and it is unknown whether hearing loss early in midlife represents a risk factor for dementia. We examined whether hearing loss diagnosed in midlife was associated with an increased risk of dementia. A cohort comprising 942,567 Danish men enrolled in the mandatory conscription board examination was followed from conscription (age 19). Cognitive ability was measured at conscription, while hearing loss was ascertained either by physicians diagnosis at conscription or by the Danish National Patient Registry from 1977 to 2016 (ICD-8:388; 389; ICD-10:H90; H91). Differences in cognitive ability in relation to hearing loss at conscription were calculated using t test, while the risk of dementia associated with hearing loss was estimated using Cox regression with adjustment for cognitive ability, education, depression, diabetes, hypertension, and cerebrovascular disease. Men with hearing loss at conscription had about 2 points (corresponding to 0.20 SD) lower mean cognitive score than those without hearing loss. During follow-up, 59,834 men had a hearing loss diagnosis, while 9114 were diagnosed with dementia. Midlife hearing loss was associated with an increased rate of dementia diagnosed before age 60 (adjusted Hazard Ratio (HR) = 1.90 [95% CI 1.59-2.76]) or at a later age (adjusted HR = 1.15 [95% CI 1.06-1.25]). Our study supports the evidence that early identification and correction of hearing loss holds promise for prevention of dementia later in life.

Labor augmentation during birth and later cognitive ability in young adulthood.

PURPOSE: Synthetic oxytocin for labor augmentation during birth has been linked to negative neurodevelopment effects in children. We examined whether maternal labor augmentation was associated with lower cognitive ability in young adulthoods. PATIENTS AND METHODS: We identified 330,107 individuals (96.6% were men), with noninduced labor and with a cognitive ability test score, the Børge Priens Prøve (BPP) score, from draft board examinations in 1995-2015 (mean age, 18.8 years). Information on maternal labor augmentation was ascertained from the Danish Medical Birth Register, and we calculated mean differences in the BPP score according to maternal labor augmentation. We repeated our analyses in a sub-sample of siblings to control for unmeasured familial confounding. RESULTS: Maternal labor augmentation was not associated with any noticeable decline in cognitive ability. However, the difference in the mean BPP score for exposure to maternal labor augmentation varied according to maternal parity, as the mean difference in BPP scores increased with increasing parity, in nulliparous: mean difference=-0.14 (95% CI=-0.23 to -0.04); in maternal parity 4+: mean difference=-1.21 (95% CI=-2.905 to -0.37). The sibling analysis showed little influence of shared familial factors on the association. CONCLUSION: The mean BPP was slightly lower among labor augmented compared to nonaugmented and with an increasing difference with increasing parity. However, the differences were small and could not be considered of any clinical relevance. Furthermore, the sibling analyses suggested little confounding by familial factors.

Young adult cognitive ability and subsequent major depression in a cohort of 666,804 Danish men.

BACKGROUND: Early life cognitive ability (CA) might influence the risk of developing major depression (MD). The aim was to investigate the association between young adult CA and subsequent MD in relation to different MD disease characteristics. METHODS: Information on CA was assessed at conscription board examinations 1957-1984 (mean age 19 years) and information on MD was based on hospital diagnosis retrieved from Danish Patient registers 1969-2015. Associations between CA and MD were examined using Cox regression analyses. RESULTS: A total of 666,804 men (born 1939-1959) were followed and 25,841 (3.9%) developed MD during a mean follow-up of 40.8 years. Lower CA was associated with an increased risk of incident MD. The association was stronger for early-onset (<60 years) (HRper1SDdecrease = 1.23; 95%CI:1.21,1.24) compared to late-onset (≥60 years) MD (HRper1SDdecrease = 1.14; 95%CI:1.11,1.16), but CA was not related to number of depressive episodes. The association was stronger for single depressive episodes (HRper1SDdecrease = 1.21; 95%CI:1.19,1.23) compared to recurrent depression (HRper1SDdecrease = 1.13; 95%CI:1.09,1.16), while the strength of the association did not differ according to MD disease severity (ICD10: mild, moderate, and severe depression). LIMITATIONS: The study sample only included men and only MD cases diagnosed at hospital were included which limits the generalizability. CONCLUSION: Low CA could be a risk factor for especially early onset MD in men, whereas the influence of CA on re-occurrence seems less strong. Lower pre-morbid CA increases the risk of MD and should therefore be part of the depression risk assessment in clinical practice.

Electroconvulsive therapy and risk of dementia in patients with affective disorders: a cohort study.

BACKGROUND: Electroconvulsive therapy (ECT) is the most effective treatment for severe episodes of mood disorders. Temporary memory loss is a common side-effect, but ongoing discussions exist regarding potential long-term adverse cognitive outcomes. Only a few studies have examined the frequency of dementia in patients after ECT. The aim of this study was to examine the association between ECT and risk of subsequent dementia in patients with a first-time hospital diagnosis of affective disorder. METHODS: We did a cohort study of patients aged 10 years and older in Denmark with a first-time hospital contact for an affective disorder from Jan 1, 2005, through Dec 31, 2015, identified in the Danish National Patient Registry with ICD-10 codes F30.0 to F39.9. From the registry we retrieved information on all ECTs registered for patients and followed up patients for incidental dementia (defined by hospital discharge diagnoses or acetylcholinesterase inhibitor use) until Oct 31, 2016. We examined the association between ECT and dementia using Cox regression analyses with multiple adjustments and propensity-score matching on sociodemographic and clinical variables. FINDINGS: Of 168 015 patients included in the study, 5901 (3·5%) patients had at least one ECT. During the median follow-up of 4·9 years (IQR 2·4-7·8) and 872 874 person years, the number of patients who developed dementia was 111 (0·1%) of 99 045 patients aged 10-49 years, 965 (2·7%) of 35 945 aged 50-69 years, and 4128 (12·5%) of 33 025 aged 70-108 years. 217 (3·6%) of the 5901 patients treated with ECT developed dementia, whereas of 162 114 patients not treated with ECT 4987 (3·1%) developed dementia. The corresponding incidences were 70·4 cases per 10 000 person-years (95% CI 61·6-80·5) and 59·2 per 10 000 person-years (57·6-60·8). In patients younger than 50 years and 50-69 years, ECT was not associated with a risk of dementia compared with age-matched patients who were not given ECT (age-adjusted hazard ratio [HR] 1·51, 95% CI 0·67-3·46, p=0·32; and 1·15, 0·91-1·47, p=0·22, respectively). In patients aged 70 years and older, ECT was associated with a decreased rate of dementia (0·68, 95% CI 0·58-0·80; p<0·0001), but in the propensity-score matched sample the HR was attenuated (0·77, 0·59-1·00; p=0·062). 31 754 patients (17·6%) died during follow-up (mortality rate per 1000 person-years 35·7, 95% CI 35·3-36·2) and supplementary analyses suggested that the risk of dementia, taking the competing mortality risk into account, was not significantly associated with ECT (subdistribution HR 0·98, 95% CI 0·76-1·26; p=0·24). INTERPRETATION: ECT was not associated with risk of incidental dementia in patients with affective disorders after correcting for the potential effect of patient selection or competing mortality. The findings from this study support the continued use of ECT in patients with severe episodes of mood disorders, including those who are elderly. FUNDING: Danish Council for Independent Research, Danish Medical Research Council, the Velux Foundation, the Jascha Foundation, and the Doctor Sofus Carl Emil Friis and Olga Doris Friis grant.

The association between depression and mortality - a comparison of survey- and register-based measures of depression.

BACKGROUND: A number of studies have associated depression with a high mortality risk. However, in surveys, depression is often measured by self-reports in selected sub-samples, while register studies have been based on hospital diagnosis or purchase of antidepressants. We examined how different survey- and register-based measures of depression were associated with 7-year mortality in a cohort of middle-aged Danish men. METHODS: The study was based on 10,517 men born in 1953. Depression was assessed through hospital diagnosis for the period from 1969 to 2004 and by self-reported information on depression, use of antidepressants and the Major Depression Inventory (MDI) from a survey in 2004, in which 58.8% (n=6292) of the men participated. Information on mortality and cause of death was retrieved from registers for the period between 2004 and 2011. RESULTS: Depression diagnosis from hospital registers as well as self-reported depression, use of antidepressants and having a high MDI-score were significantly associated with mortality from all, natural and unnatural causes. The associations were of a similar magnitude for the register-based measure of depression and for the survey-based measures reflecting past depression, but the strongest association was found for current depression as assessed by the MDI-score. LIMITATIONS: The study population consists almost exclusively of white men and the findings may not be generalizable to female populations or other races and ethnicities. CONCLUSIONS: Physicians should be aware of male patients with a history of depression from hospital records or self-reported as they have higher mortality risk years after their first symptom.

The U-shaped association of body mass index with mortality: Influence of the traits height, intelligence, and education.

OBJECTIVE: The U-shaped association between body mass index (BMI) and mortality may depend on other traits with permanent health effects. Whether the association between BMI and mortality depends on levels of health-related traits known to be inversely associated with mortality throughout adult life such as height, intelligence, and education was investigated. METHODS: The study was based on a cohort of young men with data on weight, height, intelligence test score, and education from the Danish Conscription Database. In total, 346,500 men born 1939 to 1959 were followed until December 2013. The association between BMI and mortality was analyzed using Cox-regression models including interactions between BMI and height, intelligence, and education, respectively. RESULTS: BMI and mortality showed the U-shaped association from the start of the follow-up period, and it persisted through the subsequent 56 years. As expected, the mortality was inversely associated with height, intelligence, and education, but the U shape of the association between BMI and mortality was unaffected by the levels of these traits except at higher BMI values, where the slopes were steeper for men with higher levels of height, intelligence, and education. CONCLUSIONS: High and low BMI was associated with higher mortality throughout life regardless of the levels of height, intelligence, and education.

Cohort Profile: The Danish Conscription Database(DCD): A cohort of 728,160 men born from 1939 through 1959.

The Danish Conscription Database (DCD) was established to enable studies of the influence of early physical and mental exposures on adverse health and social outcomes from a life-course perspective. In Denmark, all young men are requested to appear before the conscription board when they turn 18 years, to be assessed for military service. The DCD was established by digitizing information from conscription board register cards on the height, weight, educational level, intelligence test score and examination details of Danish conscripts. The DCD contains information on 728,160 men born from 1939 through 1959 and examined by the conscription board from 1957 through 1984. The unique Danish personal identification number of each individual conscript has been traced, and this allows linkage of the DCD to all Danish health and socioeconomic registers. More than 130,000 deaths have been identified in a recent linkage to the Danish Register of Cause of Death. We encourage collaboration, and interested researchers should contact: danishconscriptiondatabase.glostrup-hospital@regionh.dk.