Cognitive ability in adolescence and mortality in middle age: a prospective life course study

The impact of AUD on death for men with different IQ-scores: a register-based cohort study of 645 955 men

AIM

To investigate whether the effect of alcohol use disorder (AUD) on death by natural and unnatural causes, respectively, differs according to intelligence quotient (IQ) scores.

METHODS

We followed 654 955 Danish men, including 75 267 brothers, born between 1939 and 1959 from their 25th birthday, 1 January 1970, or date of conscription (whichever came last) until 31 December 2018. The exposure of AUD was defined by first registered treatment (diagnosis since 1969, prescription medicine since 1994, or other treatment since 2006), and the outcomes of death by natural and unnatural causes, respectively, were obtained from nationwide registers since 1970. Information on IQ score was retrieved at conscription from the Danish Conscription Database.

RESULTS AND CONCLUSION

In total, 86 106 men were defined with an AUD. AUD combined with the highest, middle, and lowest IQ score tertiles, respectively, were associated with a 5.90 (95% confidence interval [CI] 5.75; 6.01), 6.88 (95% CI: 6.73; 7.04), and 7.53 (95% CI: 7.38; 7.68) times higher hazard of death by natural causes compared with no AUD and the highest IQ score tertile. The risk of death by unnatural causes was comparable for men with AUD regardless of IQ score tertile. A within-brother analysis showed that the impact of AUD on death by natural and unnatural causes, respectively, did not vary between men with different IQ score tertiles, but were hampered by statistical uncertainty. Our study indicates a need of special focus on men with lower levels of IQ score and AUD for prevention of death by natural causes.

Determinants of Lifestyle Choices Among South Korean College Students: An Experimental Analysis

Purpose

Based on theoretical predictions from human capital theory, the aim of this exploratory study is to analyze the relationship between experimentally elicited, incentivized economic preference parameters, Big Five and Grit personality traits, cognitive ability, and the Alameda Seven lifestyles: smoking, drinking excessively, being overweight or obese, experiencing stress, following a healthy diet, exercising, and sleeping enough. In addition, self-reported general physical and mental health are analyzed.

Materials and Methods

Data collection took place in an incentivized paper-and-pencil experiment. Undergraduate students were recruited as subjects, with the requirement that they be freshmen, but no restrictions based on gender, major, or age. A pre-test and three experimental sessions were conducted in March and in April 2018, with a total of 178 subjects participating. After deleting observations with missing values, a total of n = 138 subjects remained. Regression analysis (multivariate probit models, resulting marginal effects and changes in predicted probabilities of adopting a lifestyle for “ideal types”) was used to analyze and compare the determinants of the Alameda Seven health behaviors.

Results

Findings suggest that preference parameters, a measure of cognitive ability, and Big Five personality traits are statistically significantly estimated in regressions for the determinants of adopting Alameda Seven health behaviors, but the Grit score is only statistically significantly estimated in a regression for the determinants of reported better general mental health.

Conclusion

The findings regarding preference parameters partly lend support to predictions from human capital theory and partly confirm previous findings in health psychology. Those results might be explained by the relatively small sample size and the inclusion of a measure of cognitive ability in addition to personality traits and preferences.

Risk Behaviors Associated with Alcohol Consumption Predict Future Severe Liver Disease

BACKGROUND

Excess consumption of alcohol can lead to cirrhosis, but it is unclear whether the type of alcohol and pattern of consumption affects this risk.

AIMS

We aimed to investigate whether type and pattern of alcohol consumption early in life could predict development of severe liver disease.

METHODS

We examined 43,242 adolescent men conscribed to military service in Sweden in 1970. Self-reported data on total amount and type of alcohol (wine, beer, and spirits) and risk behaviors associated with heavy drinking were registered. Population-based registers were used to ascertain incident cases of severe liver disease (defined as cirrhosis, decompensated liver disease, liver failure, hepatocellular carcinoma, or liver-related mortality). Cox regression models were used to estimate hazard ratios for development of severe liver disease.

RESULTS

During follow-up, 392 men developed severe liver disease. In multivariable analysis, after adjustment for BMI, smoking, use of narcotics, cardiovascular fitness, cognitive ability, and total amount of alcohol, an increased risk for severe liver disease was found in men who reported drinking alcohol to alleviate a hangover ("eye-opener"; aHR 1.47, 95% CI 1.02-2.11) and men who reported having been apprehended for being drunk (aHR 2.17, 95% CI 1.63-2.90), but not for any other risk behaviors. Wine consumption was not associated with a reduced risk for severe liver disease compared to beer and spirits.

CONCLUSIONS

Certain risk behaviors can identify young men with a high risk of developing severe liver disease. Wine consumption was not associated with a reduced risk for severe liver disease compared to beer and spirits.

High BMI in late adolescence predicts future severe liver disease and hepatocellular carcinoma: a national, population-based cohort study in 1.2 million men

OBJECTIVE

A high body mass index (BMI) is associated with an increased risk for severe liver disease. It is unclear if this risk differs across BMI categories, and if the association is partially attributed to development of type 2 diabetes mellitus (T2DM).

DESIGN

We used register data from more than 1.2 million Swedish men enlisted for conscription between 1969 and 1996. Data regarding new events of severe liver disease and T2DM during follow-up were obtained by record-linkage of population-based registers. We used Cox regression to estimate adjusted HRs for future inpatient care and mortality in severe liver disease and incidence of hepatocellular carcinoma (HCC) across BMI categories, using BMI of 18.5-22.5 kg/m² as reference.

RESULTS

During a follow-up of more than 34 million person-years, 5281 cases of severe liver disease including 251 cases of HCC were identified. An association with severe liver disease was found for overweight (HR 1.49, 95% CI 1.35 to 1.64) and for obese men (HR 2.17, 95% CI 1.82 to 2.59). Development of T2DM further increased the risk for severe liver disease across all BMI categories, for instance, men with obesity and T2DM had a higher risk of severe liver disease (HR 3.28, 95% CI 2.27 to 4.74) than men with obesity free of T2DM (HR 1.72, 95% CI 1.72 to 2.54).

CONCLUSIONS

A high BMI in late adolescent men was associated with an increased risk of future severe liver disease, including HCC. Development of T2DM during follow-up was associated with a further increased risk of severe liver disease, independent of baseline BMI.

Alcohol consumption in late adolescence is associated with an increased risk of severe liver disease later in life

BACKGROUND & AIMS

High alcohol consumption is associated with an increased risk of severe liver disease. Current recommendations suggest it is safe for men to consume 30 grams of alcohol per day. We investigated the association between alcohol consumption early in life and later development of severe liver disease.

METHODS

We used data on alcohol consumption at conscription to military service from 43,296 men (18-20 years) in Sweden between 1969 and 1970. Outcomes were defined as incident diagnoses of severe liver disease from systematic national registration of clinical events until the end of 2009. A Cox regression model adjusted for body mass index, smoking, use of narcotics, cognitive ability and cardiovascular capacity was applied.

RESULTS

During a mean follow-up of 37.8 years, 383 men developed severe liver disease. Alcohol consumption was associated with an increased risk of development of severe liver disease in a dose-response pattern (adjusted hazard ratio for every one gram/day increase 1.02; 95% CI 1.01-1.02). No evidence of a threshold effect was found. Importantly, a clear trend pointed towards an increased risk of severe liver disease in men who consumed less than 30 grams of alcohol per day.

CONCLUSION

Alcohol consumption in young men is associated with an increased risk of severe liver disease, up to 39 years later in life. The risk was dose-dependent, with no sign of a threshold effect. Current guidelines for safe alcohol intake in men might have to be revised.

LAY SUMMARY

We investigated more than 43,000 Swedish men in their late teens enlisted for conscription in 1969-1970. After almost 40 years of follow-up, we found that alcohol consumption was a significant risk factor for developing severe liver disease, independent of confounders. This risk was dose-dependent, and was most pronounced in men consuming two drinks per day or more.

Childhood IQ and survival to 79: Follow-up of 94% of the Scottish Mental Survey 1947

OBJECTIVE

To extend previous literature that suggests higher IQ in youth is associated with living longer. Previous studies have been unable to assess reliably whether the effect differs across sexes and ages of death, and whether the effect is graded across different levels of IQ.

METHODS

We test IQ-survival associations in 94% of the near-entire population born in Scotland in 1936 who took an IQ test at age 11 (n = 70,805) and were traced in a 68-year follow-up.

RESULTS

Higher IQ at age 11 years was associated with a lower risk of death (HR = 0.80, 95% CI = 0.79, 0.81). The decline in risk across categories of IQ scores was graded across the full range with the effect slightly stronger in women (HR = 0.79, 95% CI = 0.77, 0.80) than in men (HR = 0.82, 95% CI = 0.81, 0.84). Higher IQ had a significantly stronger association with death before and including age 65 (HR = 0.76, 95% CI = 0.74, 0.77) than in those participants who died at an older age (HR = 0.79, 95% CI = 0.78, 0.80).

CONCLUSIONS

Higher childhood IQ is associated with lower risk of all-cause mortality in both men and women. This is the only near-entire population study to date that examines the association between childhood IQ and mortality across most of the human life course.

Higher IQ in childhood is linked to a longer life

New data on cause of death suggest the link is mediated by risk factors such as smoking

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.

Overweight in late adolescence predicts development of severe liver disease later in life: A 39years follow-up study

BACKGROUND & AIMS

The increased prevalence of overweight has been suggested to contribute to the worldwide increase in liver diseases. We investigated if body mass index (BMI) in late adolescence predicts development of severe liver disease later in life.

METHODS

We performed a cohort study using data from 44,248 men (18-20years) conscribed to military service in Sweden between 1969 and 1970. Outcome data were collected from national registers to identify any diagnosis of severe liver disease (i.e., diagnosis of decompensated liver disease, cirrhosis or death in liver disease) until the end of 2009. A Cox regression model was applied using BMI as independent variable. The model was adjusted for use of alcohol, use of narcotics, smoking, high blood pressure and cognitive ability at time of conscription.

RESULTS

During a follow-up period of a mean of 37.8years, 393 men were diagnosed with severe liver disease (mean time to diagnosis 24.7years). BMI (Hazard ratio [HR]=1.05 for each unit increase in BMI, 95% confidence interval [CI]: 1.01-1.09, p=0.008) and overweight (HR=1.64 for BMI 25-30 compared to BMI 18.5-22.5, 95% CI: 1.16-2.32, p=0.006) were associated with an increased risk of development of severe liver disease.

CONCLUSIONS

Being overweight in late adolescence is a significant predictor of severe liver disease later in life in men.

LAY SUMMARY

We investigated close to 45,000 Swedish men in their late teens enlisted for conscription in 1969-1970. After almost 40years of follow-up, we found that being overweight was a risk factor for developing severe liver disease, independent of established risk factors such as alcohol consumption.

Intelligence in youth and health at age 50

Background

The link between intelligence in youth and all-cause mortality in later-life is well established. To better understand this relationship, the current study examines the links between pre-morbid intelligence and a number of specific health outcomes at age 50 using the NLSY-1979 cohort.

Methods

Participants were the 5793 participants in the NLSY-79 who responded to questions about health outcomes at age 50. Sixteen health outcomes were examined: two were summary measures (physical health and functional limitation), 9 were diagnosed illness conditions, 4 were self-reported conditions, and one was a measure of general health status. Linear and logistic regressions were used, as appropriate, to examine the relationship between intelligence in youth and the health outcomes. Age, sex and both childhood and adult SES, and its sub-components – income, education, & occupational prestige – are all adjusted for separately.

Results & conclusion

Higher pre-morbid intelligence is linked with better physical health at age 50, and a lower risk for a number of chronic health conditions. For example, a 1 SD higher score in IQ was significantly associated with increased odds of having good, very good, or excellent health, with an odds ratio of 1.70 (C.I. 1.55–1.86). Thirteen of the illness outcomes were significantly and negatively associated with IQ in youth; the odds ratios ranged from 0.85 for diabetes/high blood sugar to 0.65 for stroke, per one standard deviation higher score in IQ. Adjustment for childhood SES led to little attenuation but adult SES partially mediated the relationship for a number of conditions. Mediation by adult SES was not consistently explained by any one of its components—income, education, and occupation status. The current findings contribute to our understanding of lower intelligence as a risk factor for poor health and how this may contribute to health inequalities.

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We examined links between intelligence in youth and health at age 50 in NLSY-1979.

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Higher intelligence in youth is linked with better physical health at age 50.

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Higher intelligence in youth is linked with lower risk for chronic illnesses.

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Adult but not childhood SES partially mediated the intelligence–health relationship.

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 test scores in young men and subsequent risk of type 2 diabetes, cardiovascular morbidity, and death

BACKGROUND

The association between cognitive scores in young adulthood and long-term cardiometabolic risks remains unclear.

METHODS

Using population-based registries, we followed 6502 military conscripts from their 22nd birthday until death, emigration, or 55 years of age. We calculated risks and hazard ratios (HRs) associating quartiles of cognitive scores (very high, high, moderate, and low) with type 2 diabetes, hypertension, myocardial infarction, stroke, venous thromboembolism, and death before age 55 years.

RESULTS

The 33-year risk of the combined outcome was inversely associated with cognitive scores (26% for low and 16% for very high scores). Compared with very high scores, the HR for the combined outcome was 1.20 (95% confidence interval = 1.02, 1.41) for high, 1.43 (1.22, 1.68) for moderate, and 1.67 (1.43, 1.95) for low scores. Similar HRs were observed for individual outcomes.

CONCLUSION

Low cognitive score in young adulthood was a strong predictor for type 2 diabetes, cardiovascular morbidity, and death before 55 years of age.

Psychosocial functioning and intelligence both partly explain socioeconomic inequalities in premature death. A population-based male cohort study

Objective

The possible contributions of psychosocial functioning and intelligence differences to socioeconomic status (SES)-related inequalities in premature death were investigated. None of the previous studies focusing on inequalities in mortality has included measures of both psychosocial functioning and intelligence.

Methods

The study was based on a cohort of 49 321 men born 1949–1951 from the general community in Sweden. Data on psychosocial functioning and intelligence from military conscription at ∼18 years of age were linked with register data on education, occupational class, and income at 35–39 years of age. Psychosocial functioning was rated by psychologists as a summary measure of differences in level of activity, power of initiative, independence, and emotional stability. Intelligence was measured through a multidimensional test. Causes of death between 40 and 57 years of age were followed in registers.

Results

The estimated inequalities in all-cause mortality by education and occupational class were attenuated with 32% (95% confidence interval: 20–45%) and 41% (29–52%) after adjustments for individual psychological differences; both psychosocial functioning and intelligence contributed to account for the inequalities. The inequalities in cardiovascular and injury mortality were attenuated by as much as 51% (24–76%) and 52% (35–68%) after the same adjustments, and the inequalities in alcohol-related mortality were attenuated by up to 33% (8–59%). Less of the inequalities were accounted for when those were measured by level of income, with which intelligence had a weaker correlation. The small SES-related inequalities in cancer mortality were not attenuated by adjustment for intelligence.

Conclusions

Differences in psychosocial functioning and intelligence might both contribute to the explanation of observed SES-related inequalities in premature death, but the magnitude of their contributions likely varies with measure of socioeconomic status and cause of death. Both psychosocial functioning and intelligence should be considered in future studies.

Cognitive ability in early adulthood is associated with later suicide and suicide attempt: the role of risk factors over the life course

BACKGROUND

Cognitive ability/intelligence quotient (IQ) in youth has previously been associated with subsequent completed and attempted suicide, but little is known about the mechanisms underlying the associations. This study aims to assess the roles of various risk factors over the life course in explaining the observed relationships.

METHOD

The present investigation is a cohort study based on data on IQ test performance and covariates, recorded on 49 321 Swedish men conscripted in 1969-1970, at ages 18-20 years. Information on suicides and hospital admissions for suicide attempt up to the age of 57 years, childhood and adult socio-economic position, and adult family formation, was obtained from linkage to national registers.

RESULTS

Lower IQ was associated with increased risks of both suicide and suicide attempt during the 36 years of follow-up. The associations followed a dose-response pattern. They were attenuated by approximately 45% in models controlling for social background, mental ill-health, aspects of personality and behavior, adult socio-economic position and family formation. Based on one-unit decreases in IQ test performance on a nine-point scale, the hazard ratios between ages 35 and 57 years were: for suicide 1.19 [95% confidence interval (CI) 1.13-1.25], fully adjusted 1.10 (95% CI 1.04-1.18); and for suicide attempt 1.25 (95% CI 1.20-1.31), fully adjusted 1.14 (95% CI 1.09-1.20).

CONCLUSIONS

Cognitive ability was found to be associated with subsequent completed and attempted suicide. The associations were attenuated by 45% after controlling for risk factors measured over the life course. Psychiatric diagnosis, maladjustment and aspects of personality in young adulthood, and social circumstances in later adulthood, contributed in attenuating the associations.

Childhood general mental ability and midlife psychosocial work characteristics as related to mental distress, neck/shoulder pain and self-rated health in working women and men

Psychosocial work characteristics including high demands, lack of control and poor social support have consistently been linked to poor health as has poor general mental ability (GMA). However, less is known about the relationships between stable individual factors such as GMA, psychosocial work characteristics and health.

OBJECTIVE

The present study investigated how childhood mental ability and psychosocial work characteristics relate to health in terms of mental distress, neck/shoulder pain (NSP) and self-rated health (SRH).

METHODS

Data on childhood GMA, occupational level, self-reports of demands, control and social support and health (mental distress, NSP and SRH) in midlife came from working women (n=271) and men (n=291) included in a Swedish school cohort. Hierarchical regression analyses, controlling for occupational level, were used to examine associations between childhood GMA, self-reports of high demands, low control and poor social support and the three health indicators. Taking into consideration the gendered labor market and variations in health patterns between women and men, gender specific analyses were performed.

RESULTS

There were no significant associations between childhood GMA and health indicators. Further, there were no significant interactions between GMA and psychosocial work factors. As regards the strength of the associations between GMA, psychosocial work factors and health, no consistent differences emerged between women and men.

CONCLUSIONS

In a cohort of healthy and working middle-aged women and men, self-reports of current psychosocial work characteristics seem to be more strongly linked to health, than are stable childhood factors such as GMA.

A Review of Lifetime Risk Factors for Mortality

This review was undertaken for the Faculty and Institute of Actuaries as part of their programme to encourage research collaborations between health researchers and actuaries in order to understand better the factors influencing mortality and longevity. The authors presented their findings in a number of linked sessions at the Edinburgh conference (Joining Forces on Mortality and Longevity) in October 2009 and contributed to this overview. The purpose is to review evidence for the impact on adult mortality of characteristics of the individual's lifetime socioeconomic or psychosocial environment or phenotype at the behavioural; multi-system (e.g. cognitive and physical function); or body system level (e.g. vascular and metabolic traits) that may be common risk factors for a number of major causes of death. This review shows there is growing evidence from large studies and systematic reviews that these individual characteristics, measured in pre-adult as well as the adult life, are associated with later mortality risk. The relative contribution of lifetime environment, genetic factors and chance, whether these contributions change with age, and the underlying social and biological pathways are still to be clarified. This review identifies areas where further life course research is warranted.

Intelligence in youth and all-cause-mortality: systematic review with meta-analysis

BACKGROUND

A number of prospective cohort studies have examined the association between intelligence in childhood or youth and life expectancy in adulthood; however, the effect size of this association is yet to be quantified and previous reviews require updating.

METHODS

The systematic review included an electronic search of EMBASE, MEDLINE and PSYCHINFO databases. This yielded 16 unrelated studies that met inclusion criteria, comprising 22,453 deaths among 1,107,022 participants. Heterogeneity was assessed, and fixed effects models were applied to the aggregate data. Publication bias was evaluated, and sensitivity analyses were conducted.

RESULTS

A 1-standard deviation (SD) advantage in cognitive test scores was associated with a 24% (95% confidence interval 23-25) lower risk of death, during a 17- to 69-year follow-up. There was little evidence of publication bias (Egger's intercept = 0.10, P = 0.81), and the intelligence-mortality association was similar for men and women. Adjustment for childhood socio-economic status (SES) in the nine studies containing these data had almost no impact on this relationship, suggesting that this is not a confounder of the intelligence-mortality association. Controlling for adult SES in five studies and for education in six studies attenuated the intelligence-mortality hazard ratios by 34 and 54%, respectively.

CONCLUSIONS

Future investigations should address the extent to which attenuation of the intelligence-mortality link by adult SES indicators is due to mediation, over-adjustment and/or confounding. The explanation(s) for association between higher early-life intelligence and lower risk of adult mortality require further elucidation.

Direct and indirect pathways connecting cognitive ability with cardiovascular disease risk: socioeconomic status and multiple health behaviors

OBJECTIVE

To model and test direct and indirect pathways connecting general cognitive ability (g) with cardiovascular disease risk factors, via socioeconomic status (SES) and multiple health behaviors.

METHODS

A sample comprising participants in the Health and Lifestyle Survey, a prospective cohort study of a representative sample of U.K. adults in 1984/5 (n = 4939, 2426 males).

RESULTS

Two mediating latent variables were proposed that connected a latent cognitive trait (named g) with a latent trait of cardiovascular disease (CVD) risk: multiple health behaviors (defined by smoking, physical inactivity, and weekly saturated fat intake) and SES (defined by educational attainment, occupational social class, and income). In males and females, SES mediated the association between g and CVD risk, but the mediation was moderated by years of age. A direct effect from g to CVD risk was also significant, but this was restricted to older males. Multiple health behaviors offered no explanatory power, because they were not influenced by g.

CONCLUSIONS

SES may connect g with CVD risk in males, but not systematically across the life course. Moderated mediation is a novel way to illustrate that direct and indirect pathways can vary as a function of age. Explanations that emphasize g or SES are not mutually exclusive; there are direct and indirect contributions to CVD risk from each source, and these vary across the life course.

Honeybee associative learning performance and metabolic stress resilience are positively associated

BACKGROUND

Social-environmental influences can affect animal cognition and health. Also, human socio-economic status is a covariate factor connecting psychometric test-performance (a measure of cognitive ability), educational achievement, lifetime health, and survival. The complimentary hypothesis, that mechanisms in physiology can explain some covariance between the same traits, is disputed. Possible mechanisms involve metabolic biology affecting integrity and stability of physiological systems during development and ageing. Knowledge of these relationships is incomplete, and underlying processes are challenging to reveal in people. Model animals, however, can provide insights into connections between metabolic biology and physiological stability that may aid efforts to reduce human health and longevity disparities.

RESULTS

We document a positive correlation between a measure of associative learning performance and the metabolic stress resilience of honeybees. This relationship is independent of social factors, and may provide basic insights into how central nervous system (CNS) function and metabolic biology can be associated. Controlling for social environment, age, and learning motivation in each bee, we establish that learning in Pavlovian conditioning to an odour is positively correlated with individual survival time in hyperoxia. Hyperoxia induces oxidative metabolic damage, and provides a measure of metabolic stress resistance that is often related to overall lifespan in laboratory animals. The positive relationship between Pavlovian learning ability and stress resilience in the bee is not equally established in other model organisms so far, and contrasts with a genetic cost of improved associative learning found in Drosophila melanogaster.

CONCLUSIONS

Similarities in the performances of different animals need not reflect common functional principles. A correlation of honeybee Pavlovian learning and metabolic stress resilience, thereby, is not evidence of a shared biology that will give insight about systems integrity in people. Yet, the means to resolve difficult research questions often come from findings in distant areas of science while the model systems that turn out to be valuable are sometimes the least predictable. Our results add to recent findings indicating that honeybees can become instrumental to understanding how metabolic biology influences life outcomes.