How does IQ affect onset of smoking and cessation of smoking--linking the Swedish 1969 conscription cohort to the Swedish survey of living conditions

Risk of depression following traumatic limb amputation—a general population-based cohort study

Background: Individuals with traumatic limb amputation (TLA) may be at risk of depression, but evidence of increased depression after TLA from longitudinal studies has been limited. It is also unknown whether physical function, cognitive function, and employment prior to amputation affects depression risk. We aimed to examine longitudinal associations between TLA and depression in working age men, and to explore the role of pre-amputation occupational and individual characteristics. Methods: A Swedish national register-based cohort of 189,220 men born between 1952 and 1956, and who attended conscription assessments in adolescence, was followed from 1985 to 2009. Physical, cognitive, and psychological characteristics were measured at the conscription examination, and occupational information was obtained from the 1985 census. Main outcome measures were hospital inpatient and outpatient admissions for depression. Results: In total, 401 men underwent TLA; mean age at amputation was 42.5 years (SD 7.4). Cox regression produced an unadjusted hazard ratio (95% confidence interval) of 2.61 (1.62–4.21) for risk of subsequent depression associated with TLA compared with the general population. Adjustment for occupational, physical, cognitive, and psychological characteristics did not change the association much, producing a hazard ratio of 2.53 (1.57–4.08). Conclusions: TLA is associated with an increased risk of depression in men over more than two decades of follow up. Occupational and individual characteristics prior to amputation did not greatly change depression risk following amputation. We speculate that a coordinated combination of social support and medical management may help reduce persistent depression risk in men who experience amputation.

Health literacy, cognitive ability and smoking: a cross-sectional analysis of the English Longitudinal Study of Ageing

OBJECTIVES

We used logistic regression to investigate whether health literacy and cognitive ability independently predicted whether participants have ever smoked and, in ever smokers, whether participants still smoked nowadays.

DESIGN

Cross-sectional study.

SETTING

This study used data from Wave 2 (2004-05) of the English Longitudinal Study of Ageing, which is a cohort study of adults who live in England and who, at baseline, were aged 50 years and older.

PARTICIPANTS

8734 (mean age=65.31 years, SD=10.18) English Longitudinal Study of Ageing participants who answered questions about their current and past smoking status, and completed cognitive ability and health literacy tests at Wave 2.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome measures were whether participants reported ever smoking at Wave 2 and whether ever smokers reported still smoking at Wave 2.

RESULTS

In models adjusting for age, sex, age left full-time education and occupational social class, limited health literacy (OR=1.096, 95% CI 0.988 to 1.216) and higher general cognitive ability (OR=1.000, 95% CI 0.945 to 1.057) were not associated with reporting ever smoking. In ever smokers, limited compared with adequate health literacy was associated with greater odds of being a current smoker (OR=1.194, 95% CI 1.034 to 1.378) and a 1 SD higher general cognitive ability score was associated with reduced odds of being a current smoker (OR=0.878, 95% CI 0.810 to 0.951), when adjusting for age, sex, age left full-time education and occupational social class.

CONCLUSIONS

When adjusting for education and occupation variables, this study found that health literacy and cognitive ability were independently associated with whether ever smokers continued to smoke nowadays, but not with whether participants had ever smoked.

Stress Resilience in Late Adolescence and Survival among Cancer Patients: A Swedish Register-Based Cohort Study

BACKGROUND

Chronic stress has been suggested to play a role in cancer progression, but few studies have so far examined the potential influence of stress susceptibility. This national register-based cohort study utilizes a unique data source to investigate whether a stress resilience measure is associated with survival in cancer patients.

METHODS

The cohort includes 9,318 Swedish male cancer patients born during 1952 to 1956 who had their stress resilience evaluated at a semistructured interview with a psychologist during mandatory conscription examination in late adolescence.

RESULTS

Over a median of 3 years of follow-up from cancer diagnosis, a total of 2,541 patients died (2,322 from cancer). Overall, low (23%) compared with high (25%) stress resilience was associated with increased mortality (adjusted hazard ratio estimated by Cox regression 1.45; 95% confidence interval 1.28-1.65), particularly among men with carcinomas of the oropharynx (2.62, 1.24-5.56), upper respiratory tract (4.64, 1.05-20.41), and prostate (2.20, 1.04-4.62), as well as with Hodgkin lymphoma (3.52, 1.40-8.86). An association was evident for both cancer types associated with smoking (1.35, 1.10-1.66) and malignancies without an established smoking etiology (1.32, 1.12-1.56). The association between low stress resilience and mortality could partly be explained by tumor stage, marital status, and psychiatric comorbidity at cancer diagnosis.

CONCLUSIONS

We observed an association between low stress resilience and mortality among men diagnosed with cancer, particularly oropharyngeal cancer, upper respiratory tract cancers, prostate cancer, and Hodgkin lymphoma.

IMPACT

These results suggest that individual variation in stress resilience may influence survival among men with some cancer types.

Association between lower estimated premorbid intelligence quotient and smoking behavior in patients with schizophrenia

Aim

We aimed to investigate the involvement of premorbid intelligence quotient in higher prevalence of smoking in patients with schizophrenia.

Methods

Participants included 190 patients with schizophrenia (mean ± standard deviation age: 37.7 ± 10.8 years; 88 males and 102 females) and 312 healthy individuals (mean ± standard deviation age: 38.1 ± 13.8; 166 males and 146 females), matched for age, sex, and ethnicity (Japanese). Premorbid intelligence quotient was estimated using the Japanese Adult Reading Test and distress symptoms were assessed using the Hopkins Symptom Check List. Current smoking information was collected according to self-declarations.

Results

As expected, the smoking rate was higher, while mean education level and Japanese Adult Reading Test scores were significantly lower, in patients with schizophrenia than in healthy individuals (p < 0.01). The mean education level and Japanese Adult Reading Test scores were significantly lower in the smoker group than in the non-smoker group in both patients and healthy individuals (p < 0.05). In the patient group alone, Hopkins Symptom Check List subscale and total scores were significantly higher in the smoker group than in the non-smoker group (p < 0.05). A multivariate regression analysis showed that the Japanese Adult Reading Test score was a significant and negative predictor for smoking (p < 0.001, odds ratio = 0.97; 95% confidence interval: 0.96–0.99).

Conclusion

Our results suggest that lower estimated premorbid intelligence quotient is an important variable in elucidating smoking behavior in humans and may be associated with higher prevalence of smoking in patients with schizophrenia.

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Lower premorbid intelligence quotient (IQ) was observed in patients with schizophrenia who were smokers.

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Lower education level was observed in patients with schizophrenia who were smokers.

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Lower premorbid IQ and education level were also seen in smokers in the healthy group.

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Distress symptoms were higher in smokers with schizophrenia.

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In total, premorbid IQ was a negative predictor for smoking.

Intelligence in youth and health behaviours in middle age

OBJECTIVE

We investigated the association between intelligence in youth and a range of health-related behaviours in middle age.

METHOD

Participants were the 5347 men and women who responded to the National Longitudinal Survey of Youth 1979 (NLSY-79) 2012 survey. IQ was recorded with the Armed Forces Qualification Test (AFQT) when participants were aged 15 to 23 years of age. Self-reports on exercise (moderate activity, vigorous activity, and strength training), dietary, smoking, drinking, and oral health behaviours were recorded when participants were in middle age (mean age = 51.7 years). A series of regression analyses tested for an association between IQ in youth and the different health related behaviours in middle age, while adjusting for childhood socio-economic status (SES) and adult SES.

RESULTS

Higher IQ in youth was significantly associated with the following behaviours that are beneficial to health: being more likely to be able to do moderate cardiovascular activity (Odds Ratio, 95% CI) (1.72, 1.35 to 2.20, p < .001) and strength training (1.61, 1.37 to 1.90, p < .001); being less likely to have had a sugary drink in the previous week (0.75, 0.71 to 0.80, p < .001); a lower likelihood of drinking alcohol heavily (0.67, 0.61 to 0.74, p < .001); being less likely to smoke (0.60, 0.56 to 0.65, p < .001); being more likely to floss (1.47, 1.35 to 1.59, p < .001); and being more likely to say they "often" read the nutritional information (1.20, 1.09 to 1.31, p < .001) and ingredients (1.24, 1.12 to 1.36, p < .001) on food packaging compared to always reading them. Higher IQ was also linked with dietary behaviours that may or may not be linked with poorer health outcomes (i.e. being more likely to have skipped a meal (1.10, 1.03 to 1.17, p = .005) and snacked between meals (1.37, 1.26 to 1.50, p < .001) in the previous week). An inverted u-shaped association was also found between IQ and the number of meals skipped per week. Higher IQ was also linked with behaviours that are known to be linked with poorer health (i.e. a higher likelihood of drinking alcohol compared to being abstinent from drinking alcohol (1.58, 1.47 to 1.69, p < .001)). A u-shaped association was found between IQ and the amount of alcohol consumed per week and an inverted u-shaped association was found between IQ and the number of cigarettes smoked a day. Across all outcomes, adjusting for childhood SES tended to attenuate the estimated effect size only slightly. Adjusting for adult SES led to more marked attenuation but statistical significance was maintained in most cases.

CONCLUSION

In the present study, a higher IQ in adolescence was associated with a number of healthier behaviours in middle age. In contrast to these results, a few associations were also identified between higher intelligence and behaviours that may or may not be linked with poor health (i.e. skipping meals and snacking between meals) and with behaviours that are known to be linked with poor health (i.e. drinking alcohol and the number of cigarettes smoked). To explore mechanisms of association, future studies could test for a range of health behaviours as potential mediators between IQ and morbidity or mortality in later life.

Childhood cognitive ability and smoking initiation, relapse and cessation throughout adulthood: evidence from two British cohort studies

AIMS

To test the relationship between early cognitive ability and major changes in smoking habits across adulthood, and test whether educational attainment mediates these associations.

DESIGN

Prospective observational study to examine the link between cognitive ability and smoking initiation, relapse and cessation at multiple time-points throughout adulthood in a pooled analysis of two cohorts.

SETTING

Great Britain 1981-2013.

PARTICIPANTS

A total of 16 653 participants from two British cohorts; 7191 from the 1970 British Cohort Study (BCS) and 9462 from the 1958 National Child Development Study (NCDS). Participants were 52.9% female and 27.3% were smokers, 24.8% were ex-smokers and 47.9% reported never smoking.

MEASUREMENTS

Cognitive ability was assessed at age 10 years in the BCS and 11 years in the NCDS. Outcomes were smoking initiation, relapse and cessation derived from changes in smoking status observed across five time-points between ages 26-42 in the BCS and six time-points between ages 23-55 in the NCDS. Educational attainment was examined as a mediating variable. Controls were age, gender, social class, self-control, psychological distress, parental smoking and a study indicator (BCS/NCDS).

FINDINGS

In adjusted regression models, a 1 standard deviation increase in cognitive ability predicted a 0.5 percentage point (95% CI = -0.9 to -0.1) reduced probability of smoking and a 2.9 percentage point (95% CI = 2.1-3.7) higher probability of smoking cessation throughout adulthood, but did not change the likelihood of smoking relapse significantly. Differences in educational attainment explained approximately half the association between childhood cognitive ability and smoking initiation/cessation.

CONCLUSIONS

Lower cognitive ability, measured in childhood before smoking is initiated, appears to predict a higher likelihood of taking up smoking and a lower likelihood of quitting in adulthood. Educational attainment appears to mediate this effect: children with higher cognitive ability tend to become more highly educated adults which, in turn, predicts lower rates of smoking initiation and increased rates of smoking cessation.

The evolving relationship between premorbid intelligence and serious depression across the lifespan - A longitudinal study of 43,540 Swedish men

BACKGROUND

An association between higher intelligence and lower probability of serious depression has previously been established. Yet, to our knowledge, no large prospective study has examined the relationship across the lifespan.

METHODS

A cohort of 49,321 Swedish men was followed from conscription in 1969-70 (age 18-20) through to 2008. Odds ratios (OR) for first time hospitalisation for depression (FTHD) were calculated in relation to intelligence for distinct time periods across the lifespan, while controlling for established risk factors for depression.

RESULTS

There was a linear association between higher intelligence in youth and lower odds for FTHD during the entire follow-up period, 1973-2008. The association got progressively weaker across the lifespan. During 1973-80, one step down on the stanine scale was associated with an unadjusted increase in OR of 1.34 [95% confidence interval (CI) 1.26-1.42], adjusted OR 1.23 [1.15-1.32]; while, during 2001-2008, the ORs were less than half of the magnitude of the first period, unadjusted 1.14 [1.07-1.21], and adjusted 1.09 [1.01-1.17].

LIMITATIONS

The study includes men only, and the number of available places for in-patient care decreased during the follow-up period.

CONCLUSION

For the first time, we have shown that the association between lower intelligence and depression decreases over time. The attenuation of the association in the adjusted models suggests a slower accumulation of depressogenic stressors among people with a higher IQ-score. Further exploration of intelligence's role in the etiology of depression across the lifespan is required in order to facilitate adequate diagnoses and ameliorating interventions.

Young adulthood cognitive ability predicts statin adherence in middle-aged men after first myocardial infarction: A Swedish National Registry study

Background

Cognitive ability (CA) is positively related to later health, health literacy, health behaviours and longevity. Accordingly, a lower CA is expected to be associated with poorer adherence to medication. We investigated the long-term role of CA in adherence to prescribed statins in male patients after a first myocardial infarction (MI).

Methods

CA was estimated at 18–20 years of age from Military Conscript Register data for first MI male patients (≤60 years) and was related to the one- and two-year post-MI statin adherence on average 30 years later. Background and clinical data were retrieved through register linkage with the unselected national quality register SWEDEHEART for acute coronary events (Register of Information and Knowledge about Swedish Heart Intensive Care Admissions) and secondary prevention (Secondary Prevention after Heart Intensive Care Admission). Previous and present statin prescription data were obtained from the Prescribed Drug Register and adherence was calculated as ≥80% of prescribed dispensations assuming standard dosage. Logistic regression was used to estimate crude and adjusted associations. The primary analyses used 2613 complete cases and imputing incomplete cases rendered a sample of 4061 cases for use in secondary (replicated) analyses.

Results

One standard deviation increase in CA was positively associated with both one-year (OR 1.15 (CI 1.01–1.31), P < 0.05) and two-year (OR 1.14 (CI 1.02–1.27), P < 0.05) adherence to prescribed statins. Only smoking attenuated the CA–adherence association after adjustment for a range of > 20 covariates. Imputed and complete case analyses yielded very similar results.

Conclusions

CA estimated on average 30 years earlier in young adulthood is a risk indicator for statin adherence in first MI male patients aged ≤60 years. Future research should include older and female patients and more socioeconomic variables.

Adolescent Self-Organization and Adult Smoking and Drinking over Fifty Years of Follow-Up: The British 1946 Birth Cohort

Variations in markers of adolescent self-organization predict a range of economic and health-related outcomes in general population studies. Using a population-based birth cohort study we investigated associations between adolescent self-organization and two common factors over adulthood influencing health, smoking and alcohol consumption. The MRC National Survey of Health and Development (the British 1946 birth cohort) was used to test associations between a dimensional measure of adolescent self-organization derived from teacher ratings, and summary longitudinal measures of smoking and alcohol consumption over the ensuing five decades. Multinomial regression models were adjusted for sex, adolescent emotional and conduct problems, occupational social class of origin, childhood cognition, educational attainment and adult occupational social class. With all covariates adjusted, higher adolescent self-organization was associated with fewer smoking pack years, although not with quitting; there was no association with alcohol consumption across adulthood (none or heavy compared with light to moderate). Adolescent self-organization appears to be protective against smoking, but not against heavy alcohol consumption. Interpretation of this differential effect should be embedded in an understanding of the social and sociodemographic context in which these health behaviours occur over time.

Fathers' intelligence measured at age 18-20 years is associated with offspring smoking: linking the Swedish 1969 conscription cohort to the Swedish Survey of Living Conditions

Background

An association between lower IQ of parents, measured early in life, and smoking among their offspring has been reported. The extent to which other background factors account for this association is unknown.

Methods

Data on IQ, smoking, mental health, social class, parental divorce and social problems in a cohort of men born during 1949–1951 and conscripted for military service in 1969 were linked to smoking data on 682 offspring interviewed in the Swedish Surveys of Living Conditions 1984–2009.

Results

In an age-adjusted model, a one-step decrease on a stanine scale was associated with an OR of 1.19 (95% CI 1.04 to 1.35) for offspring smoking. Adjusting for father's socioeconomic background and smoking, mental illness and social problems in youth only marginally lowered the OR's.

Conclusions

Lower IQ among fathers measured at ages 18–20 years was associated with smoking in their offspring. The association was not explained by father's social class in childhood or a higher prevalence of mental illness, social problems or smoking measured among the fathers in their late adolescence.

Intelligence and Disability Pension in Swedish Men and Women Followed from Childhood to Late Middle Age

OBJECTIVE

To investigate the association between intelligence and disability pension due to mental, musculoskeletal, cardiovascular, and substance-use disorders among men and women, and to assess the role of childhood social factors and adulthood work characteristics.

METHODS

Two random samples of men and women born 1948 and 1953 (n = 10 563 and 9 434), and tested for general intelligence at age 13, were followed in registers for disability pension until 2009. Physical and psychological strains in adulthood were assessed using job exposure matrices. Associations were examined using Cox proportional hazard regression models, with increases in rates reported as hazard ratios (HRs) with 95% confidence intervals (95%CI) per decrease in stanine intelligence.

RESULTS

In both men and women increased risks were found for disability pension due to all causes, musculoskeletal disorder, mental disorder other than substance use, and cardiovascular disease as intelligence decreased. Increased risk was also found for substance use disorder in men. In multivariate models, HRs were attenuated after controlling for pre-school plans in adolescence, and low job control and high physical strain in adulthood. In the fully adjusted model, increased HRs remained for all causes (male HR 1.11, 95%CI 1.07-1.15, female HR 1.06, 95%CI 1.02-1.09) and musculoskeletal disorder (male HR 1.16, 95%CI 1.09-1.24, female HR 1.08, 95%CI 1.03-1.14) during 1986 to 2009.

CONCLUSION

Relatively low childhood intelligence is associated with increased risk of disability pension due to musculoskeletal disorder in both men and women, even after adjustment for risk factors for disability pension measured over the life course.

Stress resilience in adolescence and subsequent antidepressant and anxiolytic medication in middle aged men: Swedish cohort study

It is unclear whether psychological resilience to stress in adolescence represents a persistent characteristic relevant to the subsequent risk for depression and anxiety in later adulthood. We aimed to test whether low psychological stress resilience assessed in adolescence is associated with an increased risk of receiving medication for depression and anxiety in middle age. We utilized Swedish register-based cohort study. Men born between 1952 and 1956 (n = 175,699), who underwent compulsory assessment for military conscription in late adolescence were followed to examine subsequent risk of pharmaceutically-treated depression and anxiety in middle age, from 2006 to 2009 corresponding to ages between 50 and 58 years, using Cox regression. The associations of stress resilience with prescription of antidepressant and anxiolytics medication through potential mediating factors cognitive and physical function and adult socioeconomic factors were calculated. Low stress resilience was associated with elevated risks for antidepressant (hazard ratio (HR):1.5 (95% CI 1.4 1.6)) and anxiolytics (HR:2.4 (CI 2.0 2.7)) medication. Adjustment for measures of childhood living circumstances attenuated the associations somewhat. Around a third of association with low stress resilience, and a half of that with moderate resilience, was mediated through cognitive and physical function in adolescence and adult socioeconomic factors. The magnitude of the inverse association of higher cognitive function with antidepressant medication was eliminated among those with low stress resilience. These results indicate that low stress resilience in adolescence is associated with an increased risk for antidepressant and anxiolytics medication over 30 years later, in part mediated through developmental factors in adolescence and socioeconomic circumstances in adulthood, and low stress resilience can diminish or eliminate the inverse association of higher cognitive function with antidepressant medication.

IQ and level of alcohol consumption—findings from a national survey of Swedish conscripts

BACKGROUND

Studies of the association between IQ and alcohol consumption have shown conflicting results. The aim of this study was to investigate the association between IQ test results and alcohol consumption, measured as both total alcohol intake and pattern of alcohol use.

METHODS

The study population consists of 49,321 Swedish males born 1949 to 1951 who were conscripted for Swedish military service 1969 to 1970. IQ test results were available from tests performed at conscription. Questionnaires performed at conscription provided data on total alcohol intake (consumed grams of alcohol/wk) and pattern of drinking. Multinomial and binomial logistic regressions were performed on the cross-sectional data to estimate odds ratios (ORs) with 95% confidence intervals (CIs). Adjustments were made for socioeconomic position as a child, psychiatric symptoms and emotional stability, and father's alcohol habits.

RESULTS

We found an increased OR of 1.20 (1.17 to 1.23) for every step decrease on the stanine scale to be a high consumer versus a light consumer of alcohol. For binge drinking, an increased OR of 1.09 (95% CI = 1.08 to 1.11) was estimated for every step decrease on the stanine scale. Adjustment for confounders attenuated the associations. Also, IQ in adolescence was found to be inversely associated with moderate/high alcohol consumption measured in middle age.

CONCLUSIONS

We found that lower results on IQ tests are associated with higher consumption of alcohol measured in terms of both total alcohol intake and binge drinking in Swedish adolescent men.

Does high intelligence improve prognosis? The association of intelligence with recurrence and mortality among Swedish men with coronary heart disease

BACKGROUND

Lower intelligence early in life is associated with increased risks for coronary heart disease (CHD) and mortality. Intelligence level might affect compliance to treatment but its prognostic importance in patients with CHD is unknown.

METHODS

A cohort of 1923 Swedish men with a measure of intelligence from mandatory military conscription in 1969-1970 at age 18-20, who were diagnosed with CHD 1991-2007, were followed to the end of 2008.

PRIMARY OUTCOME

recurrent CHD event. Secondary outcome: case fatality from the first event, cardiovascular and all-cause mortality. National registers provided information on CHD events, comorbidity, mortality and socioeconomic factors.

RESULTS

The fully adjusted HRs for recurrent CHD for medium and low intelligence, compared with high intelligence, were 0.98, (95% CIs 0.83 to 1.16) and 1.09 (0.89 to 1.34), respectively. The risks were increased for cardiovascular and all-cause mortality with lower intelligence, but were attenuated in the fully adjusted models (fully adjusted HRs for cardiovascular mortality 1.92 (0.94 to 3.94) and 1.98 (0.89 to 4.37), respectively; for all-cause mortality 1.63 (1.00 to 2.65) and 1.62 (0.94 to 2.78), respectively). There was no increased risk for case-fatality at the first event (fully adjusted ORs 1.06 (0.73 to 1.55) and 0.97 (0.62 to 1.50), respectively).

CONCLUSIONS

Although we found lower intelligence to be associated with increased mortality in middle-aged men with CHD, there was no evidence for its possible effect on recurrence in CHD.

Cognitive ability in late adolescence and disability pension in middle age: follow-up of a national cohort of Swedish males

Low cognitive ability in late adolescence has previously been shown to be associated with disability pension (DP) in young adulthood. However, most DP's are granted later in working life, and the mechanisms of the association are not fully understood. We aimed to investigate the association between cognitive ability in late adolescence and DP at ages 40-59, and investigate the role of individual and socioeconomic factors. Information on cognitive ability, health status, personality aspects and health behaviours at age 18-20 was obtained from the 1969-70 conscription cohort, comprising 49,321 Swedish men. Data on DP's 1991-2008 was obtained from the Longitudinal Database of Education, Income and Employment. Information on socioeconomic and work-related factors in childhood and adulthood was obtained from national sociodemographic databases. Hazard ratios for DP during follow-up were estimated by Cox proportional hazards models. We found a graded relationship between cognitive ability in late adolescence and DP in middle age. One step decrease on the nine-point stanine scale of cognitive ability was associated with a crude hazard ratio of 1.26 (95% CI 1.24-1.27). Socioeconomic and work-related circumstances in adulthood explained much of the association, but factors measured already in late adolescence also showed importance. The findings suggest an accumulation of risks over the life course. Although attenuated, the graded relationship remained after adjusting for all factors.

Cannabis use and depression: a longitudinal study of a national cohort of Swedish conscripts

BACKGROUND

While there is increasing evidence on the association between cannabis use and psychotic outcomes, it is still unclear whether this also applies to depression. We aim to assess whether risk of depression and other affective outcomes is increased among cannabis users.

METHODS

A cohort study of 45 087 Swedish men with data on cannabis use at ages 18-20. Diagnoses of unipolar disorder, bipolar disorder, affective psychosis and schizoaffective disorder were identified from inpatient care records over a 35-year follow-up period. Cox proportional hazard modeling was used to assess the hazard ratio (HR) of developing these disorders in relation to cannabis exposure.

RESULTS

Only subjects with the highest level of cannabis use had an increased crude hazard ratio for depression (HR 1.5, 95% confidence interval (CI), 1.0-2.2), but the association disappeared after adjustment for confounders. There was a strong graded association between cannabis use and schizoaffective disorder, even after control for confounders, although the numbers were small (HR 7.4, 95% CI, 1.0-54.3).

CONCLUSION

We did not find evidence for an increased risk of depression among those who used cannabis. Our finding of an increased risk of schizoaffective disorder is consistent with previous findings on the relation between cannabis use and psychosis.

Smoking, childhood IQ, and cognitive function in old age

OBJECTIVES

To examine the association between smoking history and cognitive function in old age, and whether it remains after controlling for childhood cognitive ability (IQ) and adult socioeconomic status (SES).

METHODS

In the Lothian Birth Cohort 1936 Study, 1080 men and women, who previously participated in a nationwide IQ-type test in childhood, were followed up at age 70. The associations between smoking history and age 70 IQ, general cognitive ability (g), processing speed, memory, and verbal ability were assessed.

RESULTS

Lower childhood IQ was associated with a higher risk of becoming a smoker and continuing to smoke in late life, and with reduced lung function (FEV1) in late life. Current smokers scored significantly lower than ex-smokers and never smokers on tests of age 70 IQ, general cognitive ability, and processing speed, but not memory or verbal ability. After controlling for childhood IQ and SES, current smoking at age 70 (but not pack years of smoking) was associated with impairments in general cognitive ability and processing speed.

CONCLUSION

Smoking in old age makes a small, independent contribution to cognitive performance in old age.

Intelligence quotient (IQ) in adolescence and later risk of alcohol-related hospital admissions and deaths--37-year follow-up of Swedish conscripts

AIMS

To investigate the relationship between intelligence measured at ages 18-19 and later alcohol-related hospital admission and mortality among men, while controlling for possible confounders.

DESIGN

Cohort study.

SETTING AND PARTICIPANTS

A total of 49,321 Swedish men who were conscripted for military training in 1969-70 and followed until 2007.

MEASUREMENTS

Intelligence quotient (IQ) measured at conscription is the exposure, while alcohol-related hospital admission and death are the two outcomes. Adjustments for following variables were made: early life circumstances [childhood socio-economic position (SEP), father's drinking], mental health, social adjustment and behavioural factors measured at age 18 (psychiatric diagnosis, contact with police and child care, low emotional control, daily smoking, risky use of alcohol) and adult social position (attained education, SEP and income at age 40).

FINDINGS

IQ had an inverse and graded association with later alcohol-related problems. For alcohol-related hospital admissions the crude hazard ratio (HR) was 1.29 (95% CI = 1.26-1.31) and for alcohol-related mortality it was 1.21 (95% CI = 1.17-1.24) for every one point decrease on the nine-point IQ scale. Adjustment for risk factors measured at age 18 attenuated the association somewhat for both outcomes. After adjustment for social position as adult, the HR was considerably lower resulting in a HR of 1.06 (95% CI = 1.02-1.10) for alcohol-related hospital admissions and 1.01 (95% CI = 0.95-1.08) for alcohol-related mortality.

CONCLUSIONS

In Swedish men there is an association between IQ in early adulthood and later alcohol-related hospital admission and death. Social position as adult could be an important contributory factor.

Neuropsychological performance in patients with schizophrenia and controls as a function of cigarette smoking status

Schizophrenia is associated with many neurocognitive deficits, some of which are improved by nicotine and cigarette smoking. To better understand the relationship between smoking and cognitive function in schizophrenia, cross-sectional assessment of neuropsychological performance as a function of smoking status (smoker or non-smoker) and smoking history (current, former or never-smoker) in clinically stable outpatients with schizophrenia and controls was evaluated. Subjects (n=140) were divided into subgroups on the basis of self-report and biochemical verification of smoking history. Current smokers with schizophrenia (n=38), former smokers with schizophrenia (n=17), never-smokers with schizophrenia (n=12), control smokers (n=31), control former smokers (n=16), and control never-smokers (n=26) were administered a comprehensive neuropsychological battery. Smokers were studied under non-deprivation conditions. Comparison of neuropsychological performance in schizophrenia and control subjects revealed significant main effects of diagnosis. Analysis of the data as a function of smoking history demonstrated that never-smokers with schizophrenia performed the poorest on measures of sustained attention, processing speed and response inhibition, when compared to the other schizophrenia subgroups. Cigarette smoking did not alter neuropsychological performance in controls. Our findings suggest that smoking status and history differentially alters neuropsychological outcomes in schizophrenia compared to non-psychiatric controls, and that never-smokers may present with more severe neurocognitive impairments.

Genetics of the association between intelligence and nicotine dependence: a study of male Swedish twins

AIMS

Previous studies have found inverse associations between intelligence quotient (IQ) and cigarette smoking, but the causal pathways linking IQ with smoking status and nicotine dependence (ND) are not well understood. The aim of this study was to explore the associations between IQ and ND using a genetically informative twin design to detect whether any association is because of shared genetic or environmental factors.

DESIGN

A population-based twin cohort with IQ measured in adolescence and ND later in life, analysed by classical twin modeling based on linear structural equations.

SETTING

Swedish national registry data.

PARTICIPANTS

A total of 5040 male twins born 1951-84.

MEASUREMENTS

IQ was measured at military conscription at a mean age of 18 years. ND was self-reported at the ages of 22-57 years using the Fagerström Test for ND scale (FTND). Both cigarette smoking and Swedish snus use were analysed.

FINDINGS

Both IQ and ND showed moderate heritability (0.58 and 0.39, respectively). The heritability of ND was similar for cigarette smoking and snus use. The phenotypic correlation between IQ and ND was weak: -0.11 (-0.16, -0.06) for total ND. Bivariate analysis revealed that this correlation was mainly because of genetic factors, but still the genetic correlation between IQ and ND from cigarette smoking was only -0.24.

CONCLUSIONS

Nicotine dependence, as measured by the Fagerström Test for Nicotine Dependence, shows moderate heritability in both smokers and snus users but is only weakly associated with intelligence quotient; common genetic factors underlying nicotine dependence and intelligence quotient probably account for little of the observed association between smoking and intelligence quotient.

Cognitive test scores in male adolescent cigarette smokers compared to non-smokers: a population-based study

BACKGROUND

Although previous studies indicate that people with lower intelligence quotient (IQ) scores are more likely to become cigarette smokers, IQ scores of siblings discordant for smoking and of adolescents who began smoking between ages 18-21 years have not been studied systematically.

METHODS

Each year a random sample of Israeli military recruits complete a smoking questionnaire. Cognitive functioning is assessed by the military using standardized tests equivalent to IQ.

RESULTS

Of 20 221 18-year-old males, 28.5% reported smoking at least one cigarette a day (smokers). An unadjusted comparison found that smokers scored 0.41 effect sizes (ES, P < 0.001) lower than non-smokers; adjusted analyses remained significant (adjusted ES = 0.27, P < 0.001). Adolescents smoking one to five, six to 10, 11-20 and 21+ cigarettes/day had cognitive test scores 0.14, 0.22, 0.33 and 0.5 adjusted ES poorer than those of non-smokers (P < 0.001). Adolescents who did not smoke by age 18, and then began to smoke between ages 18-21 had lower cognitive test scores compared to never-smokers (adjusted ES = 0.14, P < 0.001). An analysis of brothers discordant for smoking found that smoking brothers had lower cognitive scores than non-smoking brothers (adjusted ES = 0.27; P = 0.014).

CONCLUSION

Controlled analyses from this large population-based cohort of male adolescents indicate that IQ scores are lower in male adolescents who smoke compared to non-smokers and in brothers who smoke compared to their non-smoking brothers. The IQs of adolescents who began smoking between ages 18-21 are lower than those of non-smokers. Adolescents with poorer IQ scores might be targeted for programmes designed to prevent smoking.

Associations between IQ and cigarette smoking among Swedish male twins

It has been suggested that certain health behaviours, such as smoking, may operate as mediators of the well-established inverse association between IQ and mortality risk. Previous research may be afflicted by unadjusted confounding by socioeconomic or psychosocial factors. Twin designs offer a unique possibility to take genetic and shared environmental factors into account. The aim of the present national twin study was to determine the interrelations between IQ at age 18, childhood and attained social factors and smoking status in young adulthood and mid-life. We studied the association between IQ at age 18 and smoking in later life in a population of 11 589 male Swedish twins. IQ was measured at military conscription, and data on smoking and zygosity was obtained from the Swedish Twin Register. Information on social factors was extracted from censuses. Data on smoking was self-reported by the twins at the age of 22-47 years. Logistic regression models estimated with generalised estimating equations were used to explore possible associations between IQ and smoking among the twins as individuals as well as between-and within twin-pairs. A strong inverse association between IQ and smoking status emerged in unmatched analyses over the entire range of IQ distribution. In within-pair and between-pair analyses it transpired that shared environmental factors explained most of the inverse IQ-smoking relationship. In addition, these analyses indicated that non-shared and genetic factors contributed only slightly (and non-significantly) to the IQ-smoking association. Analysis of twin pairs discordant for IQ and smoking status displayed no evidence that non-shared factors contribute substantially to the association. The question of which shared environmental factors might explain the IQ-smoking association is an intriguing one for future research.

IQ, socioeconomic status, and early death: The US National Longitudinal Survey of Youth

OBJECTIVE

To assess whether the association between cognitive ability (IQ) and early mortality is mediated by socioeconomic status (SES) or whether the association between SES and mortality reflects a spurious association caused by IQ.

METHODS

The participants were from the US National Longitudinal Survey of Youth (n = 11,321). IQ was assessed at age 16 to 23 years and the participants were followed up to 40 to 47 years of age.

RESULTS

Controlling for sex, birth year, race/ethnicity, baseline health, and parental education, higher IQ was associated with lower probability of death (odds ratio (OR) per 1-standard deviation increase in IQ = 0.78, 95% confidence interval (CI) = 0.66, 0.91). This association disappeared (OR = 0.99, 95% CI = 0.81, 1.20) when adjusted for education and household income. Adjustment for IQ had no effect on the association between SES and mortality. These findings were similar in Hispanic, Black, and White/other participants and in women and men. Parental education moderated the IQ-mortality association so that this association was not observed in participants with low parental education.

CONCLUSIONS

Low IQ predicts early mortality in the US population and this association is largely explained by SES. The results do not support the alternative hypothesis that the socioeconomic gradient in early mortality would reflect IQ differences.