Level of cognitive performance as a correlate and predictor of health behaviors that protect against cognitive decline in late life: The path through life study

The Long-Term Impacts of Dementia on Preventive Care Utilization and Health Behaviors

Dementia has large impact on individuals' decision making, independent living, and wellbeing. Identifying early signals of dementia risk may offer people more time to prepare for the future, helping to delay the onset or slow the progression of dementia. Using the 1995-2018 waves of Health and Retirement Study, we offer novel evidence on the impacts of dementia on a rich set of preventive care utilization and health behaviors. Leveraging both within- and between-individual variations in an event study design, we characterize long-term dynamic changes in preventive care and health behaviors relative to the incidence of dementia and find early behavioral indicators of the disorder. We show that relative to the group of people who never develop dementia during the study periods, people with dementia have consistent and escalating declines in the use of cholesterol test, dental visit, prostate test and mammogram around the incidence of dementia. Significant declines are also found in physical activities and social engagement. Importantly, we demonstrate that the behavioral changes can occur up to 6 years before the incidence of dementia; and these patterns are absent in other chronic or acute conditions. The results are robust to sample selection, model specification, and the further control of aging and cohort effects. Overall, our findings highlight the salient impact of dementia risk on preventive care utilization and health behaviors, which may increase individuals' vulnerability to health shocks. Detecting early signals of dementia and facilitating targeted interventions are thus called for to prevent individuals from adverse behavioral and health consequences.

Can Intelligence Affect Alcohol-, Smoking-, and Physical Activity-Related Behaviors? A Mendelian Randomization Study

People with high levels of intelligence are more aware of risk factors, therefore choosing a healthier lifestyle. This assumption seems reasonable, but is it true? Previous studies appear to agree and disagree. To cope with the uncertainty, we designed a mendelian randomization (MR) study to examine the causal effects of genetically proxied intelligence on alcohol-, smoking-, and physical activity (PA)-related behaviors. We obtained genome-wide association study (GWAS) datasets concerning these variables from separate studies or biobanks and used inverse-variance weighted (IVW) or MR-Egger estimator to evaluate the causal effects according to an MR protocol. The MR-Egger intercept test, MR-PRESSO, and funnel plots were employed for horizontal pleiotropy diagnosis. The Steiger test (with reliability test), Cochran's Q test, MR-PRESSO, and leave-one-out method were employed for sensitivity analysis. We found significant or potential effects of intelligence on alcohol dependence (OR = 0.749, p = 0.003), mental and behavioral disorders due to alcohol (OR = 0.814, p = 0.009), smoking (OR = 0.585, p = 0.005), and smoking cessation (OR = 1.334, p = 0.001). Meanwhile, we found significant or potential effects on walking duration (B = -0.066, p < 0.001), walking frequency (B = -0.055, p = 0.031), moderate PA frequency (B = -0.131, p < 0.001), and vigorous PA frequency (B = -0.070, p = 0.001), but all in a negative direction. In conclusion, our findings reinforce some existing knowledge, indicate the complexity of the health impacts of human intelligence, and underline the value of smoking and alcohol prevention in less intelligent populations. Given the existing limitations in this study, particularly the potential reverse causality in some estimations, re-examinations are warranted in future research.

Cognitive ability and teen smoking

We use data on 11-15-year-old boys in the West Bank to study the empirical link between cognitive ability and health behavior, specifically (teen) smoking. Adjusting for both age in months and grade level allows us to effectively shut down any simultaneous effect of maturation and schooling on cognitive ability and smoking. We find that those at the lower end of the cognitive ability distribution are more than twice as likely to smoke than those at the upper end (approximately 25 versus 10%) also after adjusting for parental background and peer composition in a generalized propensity score approach. Further, we find that the cognitive ability-smoking gradient is fairly flat at the lower end of the cognitive ability distribution and steep at the upper end.

Dietary glycaemic index and cognitive function: prospective associations in adults of the 1946 British birth cohort

Objective

Evidence suggests that the rate of glucose release following consumption of carbohydrate-containing foods, defined as the glycaemic index (GI), is inversely associated with cognitive function. To date, most of the evidence stems from either single-meal studies or highly heterogeneous cohort studies. We aimed to study the prospective associations of diet GI at age 53 years with outcomes of verbal memory and letter search tests at age 69 years and rate of decline between 53 and 69 years.

Design

Longitudinal population-based birth cohort study.

Setting

MRC National Survey for Health and Development.

Participants

Cohort members (n 1252).

Results

Using multivariable linear and logistic regression, adjusted for potential confounders, associations of higher-GI diet with lower verbal memory, lower letter search speed and lower number of hits in a letter search test were attenuated after adjustments for cognitive ability at age 15 years, educational attainment, further training and occupational social class. No association was observed between diet GI at 53 years and letter search accuracy or speed–accuracy trade-off at 69 years, or between diet GI at 53 years and rate of decline between 53 and 69 years in any cognitive measure.

Conclusions

Diet GI does not appear to predict cognitive function or decline, which was mainly explained by childhood cognitive ability, education and occupational social class. Our findings confirm the need for further research on the association between diet and cognition from a life-course perspective.

Intelligence and socioeconomic position in childhood in relation to frailty and cumulative allostatic load in later life: the Lothian Birth Cohort 1936

Background

Information on childhood determinants of frailty or allostatic load in later life is sparse. We investigated whether lower intelligence and greater socioeconomic disadvantage in childhood increased the risk of frailty and higher allostatic load, and explored the mediating roles of adult socioeconomic position, educational attainment and health behaviours.

Methods

Participants were 876 members of the Lothian Birth Cohort 1936 whose intelligence was assessed at age 11. At age 70, frailty was assessed using the Fried criteria. Measurements were made of fibrinogen, triglyceride, total and high-density lipoprotein cholesterol, albumin, glycated haemoglobin, C reactive protein, body mass index and blood pressure, from which an allostatic load score was calculated.

Results

In sex-adjusted analyses, lower intelligence and lower social class in childhood were associated with an increased risk of frailty: relative risks (95% CIs) were 1.57 (1.21 to 2.03) for a SD decrease in intelligence and 1.48 (1.12 to 1.96) for a category decrease in social class. In the fully adjusted model, both associations ceased to be significant: relative risks were 1.13 (0.83 to 1.54) and 1.19 (0.86 to 1.61), respectively. Educational attainment had a significant mediating effect. Lower childhood intelligence in childhood, but not social class, was associated with higher allostatic load. The sex-adjusted coefficient for allostatic load for a SD decrease in intelligence was 0.10 (0.07 to 0.14). In the fully adjusted model, this association was attenuated but remained significant (0.05 (0.01 to 0.09)).

Conclusions

Further research will need to investigate the mechanisms whereby lower childhood intelligence is linked to higher allostatic load in later life.

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.

Monitoring cognitive functioning: psychometric properties of the brief test of adult cognition by telephone

Assessment of cognitive functioning is an important component of telephone surveys of health. Previous cognitive telephone batteries have been limited in scope with a primary focus on dementia screening. The Brief Test of Adult Cognition by Telephone (BTACT) assesses multiple dimensions central for effective functioning across adulthood: episodic memory, working memory, reasoning, verbal fluency, and executive function. The BTACT is the first instrument that includes measures of processing speed, reaction time, and task-switching/inhibitory control for use over the telephone. We administered the battery to a national sample (N = 4,268), age 32 to 84 years, from the study of Midlife in the United States (MIDUS) and examined age, education, and sex differences; reliability; and factor structure. We found good evidence for construct validity with a subsample tested in person. Implications of the findings are considered for efficient neuropsychological assessment and monitoring changes in cognitive aging, for clinical and research applications by telephone or in person.

Do dietary patterns influence cognitive function in old age?

BACKGROUND

Evidence from observational studies to date suggests that healthy dietary patterns are associated with better cognitive performance in later life. We examined the extent to which childhood intelligence quotient (IQ) and socioeconomic status account for this association.

METHODS

Analyses were carried out on 882 participants in the Lothian Birth Cohort 1936 Study. Four dietary patterns were extracted using principal components analysis of a food frequency questionnaire, namely "Mediterranean-style," "health aware," "traditional," and "sweet foods." Cognitive function was assessed at the age of 70 years, including general (g) cognitive ability, processing speed, memory, and verbal ability.

RESULTS

Before adjustment for childhood IQ and socioeconomic status, the "Mediterranean-style" dietary pattern was associated with significantly better cognitive performance (effect size as partial eta-square (ηp(2)) range = 0.005 to 0.055), and the "traditional" dietary pattern was associated with poorer performance on all cognitive domains measured in old age (ηp(2) = 0.009 to 0.103). After adjustment for childhood IQ (measured at the age of 11 years) and socioeconomic status, statistical significance was lost for most associations, with the exception of verbal ability and the "Mediterranean-style" pattern (National Adult Reading Test (NART) ηp(2) = 0.006 and Wechsler Test of Adult Reading (WTAR) ηp(2) = 0.013), and the "traditional" pattern (NART ηp(2) = 0.035 and WTAR ηp(2) = 0.027).

CONCLUSIONS

Our results suggest a pattern of reverse causation or confounding; a higher childhood cognitive ability (and adult socioeconomic status) predicts adherence to a "healthy" diet and better cognitive performance in old age. Our models show no direct link between diet and cognitive performance in old age; instead they are related via the lifelong-stable trait of intelligence.