Childhood IQ, smoking, and cognitive change from age 11 to 64 years

The negative impact of chronic tobacco smoking on adult neuropsychological function: a cross-sectional study

Background

The evidence on the effects of chronic tobacco smoking on neuropsychological functions is conflicting. The literature remains limited by inconsistent accounting for potentially confounding biomedical and psychiatric conditions. This study aimed to assess the neuropsychological functions of adult chronic tobacco smokers in comparison to group-matched non-smokers.

Method

The study included 73 smokers and 84 group-matched non-smokers. The data was collected during the year 2019. After an initial interview to collect demographics and smoking profile, the subjects undertook neuropsychological assessments that targeted a wide range of cognitive domains.

Results

The performance of smokers was poorer on almost all neuropsychological domains, namely selective attention (p ≤ .001, p = .044), alternating attention (p = .002) working memory (p ≤ .001), Short-term memory (p = .006 and .003), Long-term memory (p ≤ .001), processing accuracy (p ≤ .001), and executive function (p = .011 and .026). Smokers were intact on processing speed. Smoking accumulation and lower age onset of regular smoking were correlated with lower neuropsychological function.

Conclusion

Our findings add to the growing body of evidence suggesting that chronic tobacco smoking impacts cognition negatively.

Circulating asymmetric dimethylarginine and cognitive decline: A 4-year follow-up study of the 1936 Aberdeen Birth Cohort

BACKGROUND

The underlying mechanisms leading to dementia and Alzheimer's disease (AD) are unclear. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, may be associated with cognitive decline, but population-based evidence is lacking.

METHODS

Change in cognitive performance was assessed in participants of the Aberdeen Birth Cohort of 1936 using longitudinal Raven's progressive matrices (RPM) between 2000 and 2004. Multiple linear regression was used to estimate the association between ADMA concentrations in 2000 and change in cognitive performance after adjustment for potential confounders.

RESULTS

A total of 93 participants had complete information on cognitive performance between 2000 and 2004. Mean plasma ADMA concentrations were approximately 0.4 μmol/L lower in those participants with stable or improved RPM scores over follow-up compared with participants whose cognitive performance worsened. In confounder-adjusted analysis, one SD (0.06 μmol/L) increase in ADMA at 63 years of age was associated with an average reduction in RPM of 1.26 points (95% CI 0.14-2.26) after 4 years.

CONCLUSION

Raised plasma ADMA concentrations predicted worsening cognitive performance after approximately 4 years in this cohort of adults in late-middle age. These findings have implications for future research, including presymptomatic diagnosis or novel therapeutic targets for dementia and AD.

Lifecourse epidemiology matures: Commentary on Zhang et al. "Early-life socioeconomic status, adolescent cognitive ability, and cognition in late midlife"

The effect of education on late life cognition has attracted substantial attention in lifecourse epidemiology, in part because of its relevance for understanding the effect of education on dementia. Although numerous studies document an association between education and later life cognition, these studies are potentially confounded by early life socioeconomic position and cognition. Good measures of these early life constructs are rarely available in data sets assessing cognition in late life. A further body of evidence has taken advantage of compulsory schooling law (CSL) instrumental variables (IV), although these estimates have been criticized based on questions about the validity of CSL IVs. In this issue of the Journal, Zhang et al. took advantage of the Wisconsin Longitudinal Study to control for both prospectively measured adolescent IQ and early life socioeconomic status in an analysis evaluating the effect of education on cognitive scores in late middle age (Zhang et al., 2019; IN THIS ISSUE). Their results indicate a moderate effect of each additional year of education on later life cognition, of approximately 0.1-0.15 standard deviations per year of schooling. These estimates are remarkably aligned with findings from prior observational designs and from the CSL IV studies. Although criticisms of any individual study are plausible, this new study complements the body of prior evidence to provide compelling evidence for the benefits of education on late life cognition.

Healthy cognitive ageing in the Lothian Birth Cohort studies: marginal gains not magic bullet

In the face of shifting demographics and an increase in human longevity, it is important to examine carefully what is known about cognitive ageing, and to identify and promote possibly malleable lifestyle and health-related factors that might mitigate age-associated cognitive decline. The Lothian Birth Cohorts of 1921 (LBC1921, n = 550) and 1936 (LBC1936, n = 1091) are longitudinal studies of cognitive and brain ageing based in Scotland. Childhood IQ data are available for these participants, who were recruited in later life and then followed up regularly. This overview summarises some of the main LBC findings to date, illustrating the possible genetic and environmental contributions to cognitive function (level and change) and brain imaging biomarkers in later life. Key associations include genetic variation, health and fitness, psychosocial and lifestyle factors, and aspects of the brain's structure. It addresses some key methodological issues such as confounding by early-life intelligence and social factors and emphasises areas requiring further investigation. Overall, the findings that have emerged from the LBC studies highlight that there are multiple correlates of cognitive ability level in later life, many of which have small effects, that there are as yet few reliable predictors of cognitive change, and that not all of the correlates have independent additive associations. The concept of marginal gains, whereby there might be a cumulative effect of small incremental improvements across a wide range of lifestyle and health-related factors, may offer a useful way to think about and promote a multivariate recipe for healthy cognitive and brain ageing.

Prospective Analysis of the Influence of Sport and Educational Factors on the Prevalence and Initiation of Smoking in Older Adolescents from Croatia

The prevalence of smoking among Croatian adolescents is alarmingly high, but no previous study has prospectively examined the sport- and academic-factors associated with smoking and smoking initiation. This study aimed to prospectively examine the associations between scholastic (educational) achievement and sport factors and smoking in 16- to 18-year-old adolescents. This two-year prospective cohort study included 644 adolescents who were 16 years of age at baseline (46% females). Baseline testing was implemented at the beginning of the 3rd year of high school (September 2014) when participants were 16 years old. Follow-up testing was completed at the end of the fourth year of high school, which occurred 20 months later. The evaluated predictor variables were educational-achievement- and sport-related-factors. The outcome variables were (i) smoking at baseline; (ii) smoking at follow-up; and (iii) smoking initiation over the course of the study. We assessed the associations between predictors and outcomes using logistic regression models adjusted for age, gender, socioeconomic status, and conflict with parents. The educational variables were consistently associated with smoking, with lower grade-point-average (Baseline: odd ratio (OR): 2.01, 95% confidence interval (CI): 1.61–2.55; Follow-up: 1.59, 1.31–1.94), more frequent absence from school (Baseline: OR: 1.40, 95% CI: 1.19–1.69; Follow-up: 1.30, 1.08–1.58), and lower behavioral grades (Baseline: OR: 1.80, 95% CI: 1.10–2.89; Follow-up: 1.57, 1.03–2.41) in children who smoke. Adolescents who reported quitting sports were at greater odds of being smokers (Baseline: 2.07, 1.31–3.32; Follow-up: 1.66, 1.09–2.56). Sport competitive achievement at baseline was protective against smoking initiation during following two-year period (0.45, 0.21–0.91). While the influence of the educational variables on smoking initiation has been found to be established earlier; sport achievement was identified as a significant protective factor against initiating smoking in older adolescents. Results should be used in development of an anti-smoking preventive campaign in older adolescents.

Sport and scholastic factors in relation to smoking and smoking initiation in older adolescents: a prospective cohort study in Bosnia and Herzegovina

OBJECTIVE

Sport and scholastic factors are known to be associated with cigarette smoking in adolescence, but little is known about the causality of this association. The aim of this study was to prospectively explore the relationships of different sport and scholastic factors with smoking prevalence initiation in older adolescents from Bosnia and Herzegovina.

METHODS

In this 2-year prospective cohort study, there were 872 adolescent participants (16 years at baseline; 46% females). The study consisted of baseline tests at the beginning of the third year (September 2013) and follow-up at the end of the fourth year of high school (late May to early June 2015). The independent variables were scholastic and sport-related factors. The dependent variables were (1) smoking at baseline, (2) smoking at follow-up and (3) smoking initiation over the course of the study. Logistic regressions controlling for age, gender and socioeconomic status were applied to define the relationships between independent and dependent variables.

RESULTS

School absence at the baseline study was a significant predictor of smoking initiation during the course of the study (OR 1.4, 95% CI 1.1 to 1.8). Those who reported quitting sports at baseline showed an increased risk of smoking at the end of the study (OR 1.4, 95% CI 1.1 to 2.0) and of smoking initiation (OR 1.8, 95% CI 1.3 to 2.0). Adolescents who reported lower competitive achievements in sport were at a higher risk of (1) smoking at baseline (OR 1.5, 95% CI 1.1 to 2.1), (2) smoking at follow-up (OR 1.5, 95% CI 1.1 to 2.1) and (3) smoking initiation (OR 1.6, 95% CI 1.1 to 2.6).

CONCLUSIONS

In developing accurate antismoking public health policies for older adolescents, the most vulnerable groups should be targeted. The results showed that most participants initiated smoking before 16 years of age. Therefore, further investigations should evaluate the predictors of smoking in younger ages.

Cigarette smoke and related risk factors in neurological disorders: An update

Cigarette smoking is known to be harmful to health, and is considered the main cause of death worldwide, especially in India. Among the well-distinguished diseases related to smoking are, chronic obstructive pulmonary disease, oral and peripheral cancers, and cardiovascular complications. However, the impact of cigarette smoking on neurocognitive and neuropathological effects, including anxiety, Alzheimer's disease, Parkinson's disease, ischemic stroke, and blood-brain barrier dysfunction, still remains unclear. Cigarette smoke consists of more than 4500 toxic chemicals that combine to form free radicals, which lead to oxidative stress-associated neurological disorders. Herein, we discuss the role of antioxidant agents in delaying or attenuating disease complications. In addition, in this review, we discuss the neuropathological effect of cigarette smoke and its interference in neurodegeneration.

Effects of cigarette smoking and alcohol use on neurocognition and BDNF levels in a Chinese population

OBJECTIVE

Few studies have examined the potential interactive effect of both smoking and drinking on cognition. Brain-derived neurotrophic factor (BDNF) plays a critical role in cognition. This is the first study to examine the neurocognitive consequences of cigarette smoking combined with chronic alcohol consumption and their relationship to serum BDNF levels in a Chinese Han population.

MATERIALS AND METHODS

We recruited 191 healthy male subjects, including 47 isolated smokers, 31 isolated chronic alcohol users, 58 combined smokers and chronic alcohol users, and 55 non-smokers and non-alcohol users. We then compared the repeatable battery for the assessment of neuropsychological status (RBANS) scores and serum BDNF levels in these four groups.

RESULTS

When compared to the non-smoking + non-alcohol-using group, the smoking group performed worse on immediate memory, attention, language, and RBANS total score. There were no significant differences in the RBANS scores between the alcohol-using group and non-smoking + non-alcohol-using group, or between the smoking group and smoking + alcohol-using group. We did not find an association between BDNF and smoking or drinking status or between BDNF and cognitive performance. In the smoking group, there was a significant correlation between BDNF and carbon monoxide concentration, and between BDNF and the Fagerstrom Test for Nicotine Dependence (FTND) total score.

CONCLUSIONS

Our results suggest that smoking is associated with cognitive decline, but not with BDNF levels in a normal population. However, smoking severity is positively associated with BDNF levels. Concomitant alcohol use does not worsen the cognitive decline caused by smoking.

Are IQ and educational outcomes in teenagers related to their cannabis use? A prospective cohort study

There is much debate about the impact of adolescent cannabis use on intellectual and educational outcomes. We investigated associations between adolescent cannabis use and IQ and educational attainment in a sample of 2235 teenagers from the Avon Longitudinal Study of Parents and Children. By the age of 15, 24% reported having tried cannabis at least once. A series of nested linear regressions was employed, adjusted hierarchically by pre-exposure ability and potential confounds (e.g. cigarette and alcohol use, childhood mental-health symptoms and behavioural problems), to test the relationships between cumulative cannabis use and IQ at the age of 15 and educational performance at the age of 16. After full adjustment, those who had used cannabis ⩾ 50 times did not differ from never-users on either IQ or educational performance. Adjusting for group differences in cigarette smoking dramatically attenuated the associations between cannabis use and both outcomes, and further analyses demonstrated robust associations between cigarette use and educational outcomes, even with cannabis users excluded. These findings suggest that adolescent cannabis use is not associated with IQ or educational performance once adjustment is made for potential confounds, in particular adolescent cigarette use. Modest cannabis use in teenagers may have less cognitive impact than epidemiological surveys of older cohorts have previously suggested.

Associations of adolescent cannabis use with academic performance and mental health: A longitudinal study of upper middle class youth

BACKGROUND

There is a hypothesis that low socioeconomic status (SES) may explain the link between cannabis use and poorer academic performance and mental health. A key question, therefore, is whether adolescent cannabis use is associated with poorer academic performance and mental health in high SES communities where there is reduced potential for confounding.

METHODS

Youth (n=254) from an upper middle class community were followed prospectively through the four years of high school (from age 14/15 to age 17/18). Past-year frequency of cannabis use was assessed annually. Official school records of academic performance and self-reported mental health symptoms (externalizing and internalizing symptoms) were assessed in grades 9 and 12.

RESULTS

Persistent cannabis use across the four years of high school was associated with lower grade-point average (β=-0.18, p=.006), lower Scholastic Aptitude Test (SAT) score (β=-0.13, p=.038), and greater externalizing symptoms (β=0.29, p<.001) in 12th grade, but not with greater internalizing symptoms (β=0.04, p=.53). Moreover, persistent cannabis use was associated with lower grade-point average (β=-0.13, p=.014) and greater externalizing symptoms (β=0.24, p=.002) in 12th grade, even after controlling for 9th grade levels of these outcomes. Similar associations were observed for persistent alcohol and tobacco use. Effects for persistent cannabis use became non-significant after controlling for persistent alcohol and tobacco use, reflecting the difficulties of disentangling effects of cannabis from effects of alcohol and tobacco.

CONCLUSIONS

Low SES cannot fully explain associations between cannabis use and poorer academic performance and mental health.

Neuropsychological functioning among chronic khat users in Jazan region, Saudi Arabia

BACKGROUND

Khat chewing effects in the central nervous system are attributed to cathinone and cathine, which are structurally related to amphetamine. However, studies on neuropsychological problems arising from khat use in humans are not extensive and have only included observational and single-case studies. The aims of this study were to (1) to examine neuropsychological functions among khat chewers, and (2) to determine factors affecting neuropsychological outcomes among khat chewers.

METHODS

A sample of 70 adult male khat chewers and a control group of 72 nonchewers were recruited from the Jazan region in southwest Saudi Arabia. A questionnaire examining socioeconomic background, medical and occupational history, education, and khat chewing behaviors was administered. Neuropsychological performance was assessed using computerized tests from the Behavioral Assessment and Research System (BARS) that assessed learning, episodic and working memory, motor speed/coordination, attention/information processing speed, sustained attention, set-shifting/response inhibition, and perceptual functions; noncomputerized tests, Trail Making A and B, Block Design, and Benton Visual Retention tests were also administered.

RESULTS

Khat chewers performed significantly worse on 3 out of 14 neuropsychological subtests compared with the control group, representing learning, motor speed/coordination, and set-shifting/response inhibition functions. Age and educational level were identified as predictors of neuropsychological outcomes of khat chewers.

CONCLUSIONS

The chronic chewing of khat leaves is associated with deficits in some neuropsychological functions, which may affect the mental and neurological health of communities in which khat chewing is a common habit.

Intellectual, neurocognitive, and academic achievement in abstinent adolescents with cannabis use disorder

RATIONALE

The active component of cannabis, delta-9 tetrahydrocannabinol (THC), has a long half-life and widespread neurocognitive effects. There are inconsistent reports of neurocognitive deficits in adults and adolescents with cannabis use disorders (CUD), particularly after a period of abstinence.

OBJECTIVES

This study aims to examine neurocognitive measures (IQ, academic achievement, attention, memory, executive functions) in abstinent adolescents with CUD, while controlling for demographic, psychopathology, and poly-substance confounders.

METHODS

We investigated neurocognitive performance in three groups: adolescents with CUD after successful first treatment and in full remission (n = 33); controls with psychiatric disorders without substance use disorder history (n = 37); and healthy adolescents (n = 43).

RESULTS

Adolescents with psychiatric disorders, regardless of CUD status, performed significantly worse than the healthy adolescents in academic achievement. No group differences were seen in IQ, attention, memory, or executive functions. Lower academic achievement was positively associated with younger age of CUD onset, regular cannabis use, and maximum daily use. In the CUD group, lifetime nicotine use episodes were negatively associated with IQ. Lower overall neurocognitive function was associated with younger age of onset of regular cannabis use and relapse within the 1 year follow-up.

CONCLUSIONS

Verifiably, abstinent adolescents with CUD history did not differ from the two comparison groups, suggesting that previously reported neurocognitive deficits may be related to other factors, including residual drug effects, preexisting cognitive deficits, concurrent use of other substances (e.g., nicotine), or psychopathology. Adolescents with CUD may not be vulnerable to THC neuropsychological deficits once they achieve remission from all drugs for at least 30 days.

Smoking-related prospective memory deficits observed on naturalistic everyday memory task

OBJECTIVE

This study assessed self-reported and objective prospective memory (PM) processes in smokers and a never-smoked comparison group. If persistent smoking does impair PM, then one would expect smokers recall being lower on a study that requires them to remember everyday activities when compared with a never-smoked group.

METHOD

An existing-groups design was used to compare a group of smokers with a never-smoked group on the self-report Prospective Memory Questionnaire (PMQ) and the Prospective Remembering Video Procedure (PRVP) measuring objective PM. An example of the location-action combination from the PRVP is 'At Thornton's shop' (location), 'Buy a bag of sweets' (action). Participants who reported using an illegal substance (e.g. ecstasy, cannabis), who drank excessively or were 'binge drinkers', or who reported suffering from a clinical condition, such as depression, were excluded from the study. Age, weekly 'safe levels' alcohol use, and strategy use were also measured and controlled for in the study. Each person was tested individually in a quiet laboratory setting on a university campus.

RESULTS

After controlling for variations in age, weekly alcohol use, and strategy use, smokers recalled significantly fewer location-action combinations on the PRVP when compared with a never-smoked group, with no between-group differences on self-reported PM as measured by the PMQ.

CONCLUSIONS

The findings suggest objective PM deficits are associated with persistent smoking - a relatively unexplored area of research. This cannot be attributed to other drug use, mood, or strategy use. The findings also suggest smokers lack self-awareness of such PM deficits. This study extends the area by utilising a more naturalistic object measure of PM and incorporating strict controls into the study.

Brain volumes and neuropsychological performance are related to current smoking and alcoholism history

BACKGROUND

Dual dependence on alcohol and nicotine is common, with many reports suggesting that more than 80% of alcoholics also smoke cigarettes. Even after cessation of alcohol consumption, many recovering alcoholics continue to smoke. In this exploratory study, we examined how current smoking and a history of alcoholism interacted in relation to brain volumes and neuropsychological performance.

METHODS

Participants were 14 abstinent long-term alcoholics (seven current smokers and seven nonsmokers), and 13 nonalcoholics (six current smokers and seven nonsmokers). The groups were equivalent in age, gender, education, and intelligence quotient. Two multiecho magnetization-prepared rapid acquisition with gradient echo (MP-RAGE) scans were collected for all participants using a 3T magnetic resonance imaging scanner with a 32 channel head coil. Brain volumes for each gray and white matter region of interest were derived using FreeSurfer. Participants completed a battery of neuropsychological tests measuring intelligence quotient, memory, executive functions, personality variables, and affect.

RESULTS

COMPARED TO NONSMOKING NONALCOHOLICS, ALCOHOLICS WHO SMOKE (THE COMORBID GROUP) HAD VOLUMETRIC ABNORMALITIES IN: pre- and para-central frontal cortical areas and rostral middle frontal white matter; parahippocampal and temporal pole regions; the amygdala; the pallidum; the ventral diencephalic region; and the lateral ventricle. The comorbid group performed worse than nonsmoking nonalcoholics on tests of executive functioning and on visually-based memory tests. History of alcoholism was associated with higher neuroticism scores among smokers, and current smoking was associated with higher sensation seeking scores and lower extraversion scores among nonalcoholics.

CONCLUSION

Results from this exploratory study support and extend prior reports showing that alcoholism and smoking, alone and in combination, are associated with structural brain abnormalities and poorer performance on neuropsychological tests. Therefore, it is important to consider smoking status in alcoholism studies and vice versa.

The role of lifestyle behaviors on 20-year cognitive decline

This study examined the association between smoking, physical activity and dietary choice at 36 and 43 years, and change in these lifestyle behaviors between these ages, and decline in verbal memory and visual search speed between 43 and 60-64 years in 1018 participants from MRC National Survey of Health and Development (NSHD, the British 1946 birth cohort). ANCOVA models were adjusted for sex, social class of origin, childhood cognition, educational attainment, adult social class, and depression; then the lifestyle behaviors were additionally mutually adjusted. Results showed that healthy dietary choice and physical activity were associated, respectively, with slower memory and visual search speed decline over 20 years, with evidence that increasing physical activity was important. Adopting positive health behaviors from early midlife may be beneficial in reducing the rate of cognitive decline and ultimately reducing the risk of dementia.

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.

A comprehensive assessment of neurocognition in middle-aged chronic cigarette smokers

BACKGROUND

The majority of studies investigating the neurocognitive consequences of chronic smoking have been conducted with adults 60 years and older. Therefore, the scope of neurocognitive dysfunction associated with chronic cigarette smoking in middle age (i.e., 30-60 age range) has not been fully delineated.

METHODS

Twenty-seven (44±9 years of age; 4 females) non-smoking and 30 smoking (49±8 years of age; 4 females) participants completed a comprehensive neurocognitive battery and measures of fine motor dexterity and postural stability. All participants were free of biomedical or psychiatric conditions that may have influenced neurocognitive and motor function.

RESULTS

Smokers performed significantly worse than non-smokers on the following domains: auditory-verbal and visuospatial learning, visuospatial memory, cognitive efficiency, executive skills, general intelligence, processing speed, fine motor dexterity and postural stability. The differences between smokers and non-smokers evidenced moderate to strong effect sizes and were not mediated by age, education, vocational level, estimated verbal intelligence or alcohol consumption. In smokers, a greater number of lifetime years of smoking was related to poorer performance on measures of cognitive efficiency, processing speed and visuospatial skills.

CONCLUSIONS

Results from this middle-aged cohort replicated previous research and provides novel findings indicating that chronic smoking was associated with inferior performance on measures of general intelligence, visuospatial learning and memory and fine motor dexterity. Research that relates measures of neurobiological function/integrity to neurocognition is needed to better understand the mechanisms contributing to the poorer performance across multiple domains demonstrated by smokers.

Smoking-related prospective memory deficits in a real-world task

BACKGROUND

Smokers, previous smokers and a never smoked group were compared on self-reported and real world prospective memory (PM - the cognitive ability of remembering to carry out particular actions at some future point in time).

METHODS

Twenty-seven current smokers, 24 people who had never smoked and 18 previous smokers were compared using an existing groups design. Scores on the long and short term PM subscales of the Prospective and Retrospective Memory Questionnaire (PRMQ) and scores on a Real World Prospective Memory Task (RWPMT) constituted the dependent measures. Smoking and other drug use were assessed by a Recreational Drug Use Questionnaire. The Hospital Anxiety and Depression Scale gauged levels of anxiety and depression. The National Adult Reading Test measured IQ, and retrospective memory was measured using the PRMQ. Gender, age, anxiety and depression, IQ, alcohol use and the retrospective memory scores, were measured as covariates and controlled for in the analysis.

RESULTS

A series of univariate ANCOVAs were applied to the main PM data across the three groups, controlling for variations in age, gender, mood, IQ, alcohol use and retrospective memory scores. These revealed no significant between-group differences on self-reported PM; however smokers recalled significantly fewer action-location combinations than the never smoked and previous smoker groups on the objective RWPMT.

CONCLUSIONS

Existing smokers showed reduced performance on RWPMT when compared to the never smoked group and previous smokers. Real-world PM impairments should be added to a growing list of neuropsychological sequelae associated with persistent smoking.

Statistical means to enhance the comparability of data within a pooled analysis of individual data in neurobehavioral toxicology

Meta-analyses of individual participant data (IPD) provide important contributions to toxicological risk assessments. However, comparability of individual data cannot be taken for granted when information from different studies has to be summarized. By means of statistical standardization approaches the comparability of data might be increased. An analysis of individual data on the neurobehavioral impact of manganese (Mn) exemplifies challenges and effects of a multilevel statistical procedure. Confounding from individual-level and study-level covariates was shown by analyses of variance, but could be reduced by linear regressions and z-normalization using data of the respective control groups. Fixed models that were used to estimate the impact of the neurotoxic exposure, provided evidence that the employed procedures, especially the z-normalization, effectively reduced variance that was unrelated to the neurotoxic exposure. Even after this statistical treatment the fixed effect models revealed differences among studies that did not seem to be exhaustively explicable by concentration differences obvious from the Mn biomarker at hand. IPD studies using confounded endpoints as effects markers can be reasonably summarized when appropriate statistical operations are employed. For the data at hand the proposed normalization allowed new insights into exposure-effect relationships, in general it appears appropriate to investigate the effect of the independent variable more closely.

Chronic cigarette smoking: implications for neurocognition and brain neurobiology

Compared to the substantial volume of research on the general health consequences associated with chronic smoking, little research has been specifically devoted to the investigation of its effects on human neurobiology and neurocognition. This review summarizes the peer-reviewed literature on the neurocognitive and neurobiological implications of chronic cigarette smoking in cohorts that were not seeking treatment for substance use or psychiatric disorders. Studies that specifically assessed the neurocognitive or neurobiological (with emphasis on computed tomography and magnetic resonance-based neuroimaging studies) consequences of chronic smoking are highlighted. Chronic cigarette smoking appears to be associated with deficiencies in executive functions, cognitive flexibility, general intellectual abilities, learning and/or memory processing speed, and working memory. Chronic smoking is related to global brain atrophy and to structural and biochemical abnormalities in anterior frontal regions, subcortical nuclei and commissural white matter. Chronic smoking may also be associated with an increased risk for various forms of neurodegenerative diseases. The existing literature is limited by inconsistent accounting for potentially confounding biomedical and psychiatric conditions, focus on cross-sectional studies with middle aged and older adults and the absence of studies concurrently assessing neurocognitive, neurobiological and genetic factors in the same cohort. Consequently, the mechanisms promoting the neurocognitive and neurobiological abnormalities reported in chronic smokers are unclear. Longitudinal studies are needed to determine if the smoking-related neurobiological and neurocognitive abnormalities increase over time and/or show recovery with sustained smoking cessation.

Smoking history and cognitive function in middle age from the Whitehall II study

BACKGROUND

Studies about the association between smoking and dementia necessarily involve those who have "survived" smoking. We examine the association between smoking history and cognitive function in middle age and estimate the risk of death and of nonparticipation in cognitive tests among smokers.

METHODS

Data are from the Whitehall II study of 10,308 participants aged 35 to 55 years at baseline (phase 1 [1985-1988]). Smoking history was assessed at phase 1 and at phase 5 (1997-1999). Cognitive data (memory, reasoning, vocabulary, and semantic and phonemic fluency) were available for 5388 participants at phase 5; 4659 of these were retested 5 years later.

RESULTS

Smokers at phase 1 were at higher risk of death (hazard ratio [HR], 2.00; 95% confidence interval [CI], 1.58-2.52 among men and HR, 2.46; 95% CI, 1.80-3.37 among women) and of nonparticipation in cognitive tests (odds ratio [OR], 1.32; 95% CI, 1.16-1.51 among men and OR, 1.69; 95% CI, 1.41- 2.02 among women). At phase 5 in age- and sex-adjusted analyses, smokers compared with those who never smoked were more likely to be in the lowest quintile of cognitive performance. After adjustment for multiple covariates, this risk remained for memory (OR, 1.37; 95% CI, 1.10-1.73). Ex-smokers at phase 1 had a 30% lower risk of poor vocabulary and low verbal fluency. In longitudinal analysis, the evidence for an association between smoking history and cognitive decline was inconsistent. Stopping smoking during the follow-up period was associated with improvement in other health behaviors.

CONCLUSIONS

Smoking was associated with greater risk of poor memory. Middle-aged smokers are more likely to be lost to follow-up by death or through nonparticipation in cognitive tests. Ex-smokers had a lower risk of poor cognition, possibly owing to improvement in other health behaviors.

Is retaining the youthful functional anatomy underlying speed of information processing a signature of successful cognitive ageing? An event-related fMRI study of inspection time performance

It has been hypothesized that individual differences in cognitive ageing might in part be based on the relative preservation of speed of information processing. However, the biological foundations of processing speed are not understood. Here we compared two groups of non-demented older people who had relatively similar IQs at age 11 but differed markedly in non-verbal reasoning ability at age 70: 'cognitive sustainers' (n=25), and 'cognitive decliners' (n=15). Using an event-related fMRI design, we studied the BOLD response while they performed an inspection time task. Inspection time is a two-alternative forced choice, backward masking test of the speed of the early stages of visual information processing. Inspection time has a well-established, significant association with higher cognitive abilities. The group of cognitive sustainers showed a pattern of BOLD activation-deactivation in response to inspection time stimulus duration differences that was similar to a healthy young sample [Deary, I.J., Simonotto, E., Meyer, M., Marshall, A., Marshall, I., Goddard, N., Watdlaw, J.M., 2004a. The functional anatomy of inspection time: an event-related fMRI study. NeuroImage 22, 1466-1479]. The group of cognitive decliners lacked these clear neural networks. The relative preservation of complex reasoning skills in old age may be associated with the preservation of the neural networks that underpin fundamental information processing in youth.

The Lothian Birth Cohort 1936: a study to examine influences on cognitive ageing from age 11 to age 70 and beyond

BACKGROUND

Cognitive ageing is a major burden for society and a major influence in lowering people's independence and quality of life. It is the most feared aspect of ageing. There are large individual differences in age-related cognitive changes. Seeking the determinants of cognitive ageing is a research priority. A limitation of many studies is the lack of a sufficiently long period between cognitive assessments to examine determinants. Here, the aim is to examine influences on cognitive ageing between childhood and old age.

METHODS/DESIGN

The study is designed as a follow-up cohort study. The participants comprise surviving members of the Scottish Mental Survey of 1947 (SMS1947; N = 70,805) who reside in the Edinburgh area (Lothian) of Scotland. The SMS1947 applied a valid test of general intelligence to all children born in 1936 and attending Scottish schools in June 1947. A total of 1091 participants make up the Lothian Birth Cohort 1936. They undertook: a medical interview and examination; physical fitness testing; extensive cognitive testing (reasoning, memory, speed of information processing, and executive function); personality, quality of life and other psycho-social questionnaires; and a food frequency questionnaire. They have taken the same mental ability test (the Moray House Test No. 12) at age 11 and age 70. They provided blood samples for DNA extraction and testing and other biomarker analyses. Here we describe the background and aims of the study, the recruitment procedures and details of numbers tested, and the details of all examinations.

DISCUSSION

The principal strength of this cohort is the rarely captured phenotype of lifetime cognitive change. There is additional rich information to examine the determinants of individual differences in this lifetime cognitive change. This protocol report is important in alerting other researchers to the data available in the cohort.

Association between mortality and cognitive change over 7 years in a large representative sample of UK residents

OBJECTIVE

To examine the association between change in reaction time and cognitive performance over 7 years and the risk of death from all causes and some specific causes after controlling for known risk factors.

METHODS

The sample comprised members of the Health and Lifestyle Survey (HALS) of community-dwelling adults in England, Scotland, and Wales. Baseline testing (HALS1), involving 9003 people, took place in 1985 and 1986. Sociodemographic, lifestyle, health, and physiological information was collected. Cognitive functioning was measured using tests of simple and choice reaction time, a short memory test, and a test of visual-spatial reasoning. Follow-up testing (HALS2) took place in 1991 and 1992, when 5352 members of the study were administered the same questionnaires, physiological examinations, and cognitive tests. The sample has been followed for mortality up to June 2005.

RESULTS

After controlling for age, gender, and the relevant baseline cognitive test scores, greater declines between HALS1 and HALS2 on simple reaction time mean and variability, choice reaction time mean and variability, memory and visual-spatial reasoning were associated with significantly increased risks of death from all causes, all cardiovascular diseases (CVDs), coronary heart disease (CHD), stroke, and respiratory disease. These associations were only slightly attenuated after adjusting for occupational social class, educational, smoking, alcohol consumption, physical activity, body mass index, blood pressure, and lung function.

CONCLUSIONS

Decline in performance of reaction times and simple cognitive tasks across a 7-year period was associated with an increased risk of death from all causes, all CVDs, CHD, stroke, and respiratory disease up to 13 years later, even after adjustment for known risk factors.

A genetic association analysis of cognitive ability and cognitive ageing using 325 markers for 109 genes associated with oxidative stress or cognition

Background

Non-pathological cognitive ageing is a distressing condition affecting an increasing number of people in our 'ageing society'. Oxidative stress is hypothesised to have a major role in cellular ageing, including brain ageing.

Results

Associations between cognitive ageing and 325 single nucleotide polymorphisms (SNPs), located in 109 genes implicated in oxidative stress and/or cognition, were examined in a unique cohort of relatively healthy older people, on whom we have cognitive ability scores at ages 11 and 79 years (LBC1921). SNPs showing a significant positive association were then genotyped in a second cohort for whom we have cognitive ability scores at the ages of 11 and 64 years (ABC1936). An intronic SNP in the APP gene (rs2830102) was significantly associated with cognitive ageing in both LBC1921 and a combined LBC1921/ABC1936 analysis (p < 0.01), but not in ABC1936 alone.

Conclusion

This study suggests a possible role for APP in normal cognitive ageing, in addition to its role in Alzheimer's disease.

Smoking has a negative impact upon health related quality of life after treatment for head and neck cancer

To examine the influence of smoking on observer based morbidity scores and patient assessed health related quality of life after treatment for head and neck cancer. The results of EORTC C30 and H&N35 questionnaires and DAHANCA morbidity scores were studied according to smoking status in 114 recurrence free head and neck cancer patients. In contrast to observer based toxicity scoring, smoking had a significantly negative influence on 20 of the 33 quality of life scales. Previous smokers had quality of life scores in between never smokers and continuous smokers. Smoking after treatment of head and neck cancer adversely influenced a wide range of quality of life endpoints. Quitters had better quality of life than patients who continued to smoke after treatment, suggesting that smoking cessation may improve quality of life in addition to reducing the risk of new cancer.

Smoking and cognitive change from age 11 to 66 years: a confirmatory investigation

Previously we reported that smoking is associated with a small relative decline in cognition from childhood to old age. In this study we perform confirmatory analyses on a further wave of data collected from 298 of the participants, all with age 11 IQ scores, at age 66years, 2years after the original observations. Non-smokers scored a mean 4.9 memory test and 2.6 information processing speed test points and ex-smokers 3.5 memory test and 1.9 information processing speed test points higher than current smokers respectively over the two waves of testing, equivalent to 4-8% of mean test scores, adjusted for the effects of childhood IQ. Across tests a 100l/min higher Peak Expiratory Flow Rate was associated with a 3-4% higher test score at ages 64 and 66years. These data confirm the adverse effect of smoking on information processing speed, and provide new evidence for a similar adverse effect on memory for people in their mid-sixties.

The association between telomere length, physical health, cognitive ageing, and mortality in non-demented older people

Telomeres are nucleo-protein complexes that protect the ends of chromosomes. The telomeric DNA component shortens each time a somatic cell replicates, eventually leading to cell senescence. Telomere length has been associated with morbidity and mortality rates from age-related diseases. We tested the hypotheses that mean peripheral blood leukocyte telomere length, at age 79 years, is associated with physical health at age 79, cognitive ability at age 79, lifetime cognitive change, smoking, alcohol consumption, social class in adulthood, and mortality in a cohort of people without dementia (the Lothian Birth Cohort 1921: LBC1921). There was a small, significant association between telomere length and verbal fluency (a test of executive function) before (r=-0.16, p=0.027) and after (r=-0.17, p=0.022) adjustment for mental ability at age 11. This might be a type 1 error. Otherwise, we find that telomere length in old age does not have a significant association with age-related physical and cognitive decline or mortality.

Cognitive impairment in elderly women: the relative importance of selected genes, lifestyle factors, and comorbidities

BACKGROUND

A variety of factors contribute to the development of cognitive impairment in elderly people. Previous studies have focused upon a single or a few risk factors. In this study we assessed and compared the significance of a wide variety of potential risk factors for cognitive impairment in postmenopausal women.

METHODS

A total of 208 pairs of elderly women (mean age = 73.2 years) were examined in a cross-sectional case-control study. Each pair consisted of a case (with impaired cognition) and a control subject matched by age and educational status. Cognitive functions were determined using a modified version of the Blessed test. Participants were also subjected to a general clinical examination and they were interviewed to collect information on lifestyle practices and comorbid disorders. Genotypes for the apolipoprotein E (APOE) epsilon4, catechol-O-methyltransferase (COMT) Val/Met, and brain-derived neurotropic growth factor (BDNF) Val/Met polymorphisms were determined. Data were analyzed by conditional logistic regression.

RESULTS

We identified a set of risk factors for age-related cognitive impairment. A statistical model for assessment of the importance of these factors was constructed. The factors in this model were physical exercise (odds ratio [OR] = 0.50, 95% confidence interval [CI] = 0.32-0.78), regular alcohol consumption (OR = 0.49, 95% CI = 0.29-0.83), metabolic syndrome (OR = 2.83, 95% CI = 1.26-6.39), depression (OR = 3.24, 95% CI = 1.28-8.22), and the APOE epsilon4 allele (OR = 1.76, 95% CI = 1.09-2.83). Also COMT genotype was present as a risk factor in the statistical model (p = 0.08).

CONCLUSIONS

Lifestyle risk factors, comorbid disorders, and genetic factors contribute to development of age-related cognitive impairment. The two former groups of risk factors appear to be particular important in this respect.

The brain-derived neurotrophic factor Val66Met polymorphism is associated with age-related change in reasoning skills

A polymorphism (Val66Met) in the gene encoding brain-derived neurotrophic factor (BDNF) has previously been associated with impaired hippocampal function and scores on the Logical Memory subtest of the Wechsler Memory Scale-Revised (WMS-R). Despite its widespread expression in the brain, there have been few studies examining the role of BDNF on cognitive domains, other than memory. We examined the association between BDNF Val66Met genotype and non-verbal reasoning, as measured by Raven's standard progressive matrices (Raven), in two cohorts of relatively healthy older people, one aged 79 (LBC1921) and the other aged 64 (ABC1936) years. LBC1921 and ABC1936 subjects had reasoning measured at age 11 years, using the Moray House Test (MHT), in the Scottish Mental Surveys of 1932 and 1947, respectively. BDNF genotype was significantly associated with later life Raven scores, controlling for sex, age 11 MHT score and cohort (P = 0.001). MHT, Verbal Fluency and Logical Memory scores were available, in later life, for LBC1921 only. BDNF genotype was significantly associated with age 79 MHT score, controlling for sex and age 11 MHT score (P = 0.016). In both significant associations, Met homozygotes scored significantly higher than heterozygotes and Val homozygotes. This study indicates that BDNF genotype contributes to age-related changes in reasoning skills, which are closely related to general intelligence.

Hormone therapy, timing of initiation, and cognition in women aged older than 60 years: the REMEMBER pilot study

OBJECTIVE

The aim of this pilot study was to assess any trends related to the timing of initiation, and duration, of hormone therapy (HT) use on cognitive function to facilitate the design and power calculations for a future large cohort study entitled Research into Memory, Brain function and Estrogen Replacement (REMEMBER).

DESIGN

A total of 428 women aged older than 60 years were recruited from a computer-generated random selection of Adelaide households. Demographic and lifestyle characteristics, and HT use history were recorded and confirmed. The Center for Epidemiological Studies-Depression score was used to assess mood. Cognitive tests were administered measuring global cognition (Mini-Mental State Examination), attention and concentration (Trail Making Test Parts A and B), verbal learning and memory (Consortium to Establish a Registry for Alzheimer's Disease [CERAD] word list immediate and delayed recall), and verbal expression (letter fluency [FAS], category fluency [Animals], and the Boston Naming Test [short form]). Analyses were adjusted for age, education, mood, body mass index, smoking, alcohol intake, and history of cerebrovascular disease. HT use was defined as the use of systemic HT for at least 1 year. Early initiation of HT use was defined as commencement of HT before age 56 years for women with a uterus and ovaries, or within 5 years of a hysterectomy and bilateral oophorectomy. Late initiation of HT use was defined as HT commencing after these times.

RESULTS

Early initiators of HT performed better than late initiators on the Mini-Mental State Examination (P = 0.04) and were faster than never users on the Trail Making Test Part A (P = 0.02). Women aged 70-79 years who initiated HT early performed better on the FAS test than never users (P = 0.0008). Late initiators performed worse than never users on the Mini-Mental State Examination (P = 0.09), and on the FAS test in the 60-69 year (P = 0.06) and 80 years and older (P = 0.095) age groups. However, late initiators performed better than never users on the FAS test in the 70-79 year age group (P = 0.015). HT users of less than 11 years (P = 0.09), HT users of more than 11 years (P = 0.04), and estrogen-only users (P = 0.024) performed faster than never users on the Trail Making Test Part A. Combined estrogen plus progestin users performed better than never users on the Boston Naming Test short form (P = 0.07).

CONCLUSIONS

For some cognitive domains, early initiation of HT from around menopause may be beneficial, and initiation of HT in late menopause may be detrimental. The timing of the initiation of HT seems critical. To fully test these hypotheses and to further examine these trends by route and type of HT regimen in this population, a study size of 2,500 women would be required.

Cognition and all-cause mortality across the entire adult age range: health and lifestyle survey

OBJECTIVE

To investigate the association of reaction time and brief measures of memory and spatial ability with all-cause mortality.

METHODS

Participants were from the UK Health and Lifestyle Survey (HALS), a national sample survey of adults in England, Scotland, and Wales. In 1984/1985, data on lifestyle factors, socioeconomic status, and health were collected for 9,003 people. Cognitive data were collected for 7,414 individuals. All-cause mortality was investigated over 19 years of follow-up in relation to simple and choice reaction time, performance on a short-term verbal declarative memory test, and on a test of visual-spatial reasoning.

RESULTS

Slower and more variable simple and choice reaction times were significantly related to increased risk of all-cause mortality over 19 years of follow-up. The increased risk of all-cause mortality was partly attenuated after adjustments for socioeconomic status, health behaviors, and health status. A novel finding was the existence of an effect of reaction time on all-cause mortality in young adults. Poorer verbal memory ability was also significantly related to an increased risk of dying in young adults independently of reaction time score.

CONCLUSION

Slower and more variable reaction time was related to higher mortality risk in younger as well as older participants. Among younger adults, higher memory ability was also associated with lower risk of dying. The cognition-mortality relationship may be explained in part by the brain's efficiency of information processing and memory performance.