Trajectories of Occupational Cognitive Demands and Risk of Mild Cognitive Impairment and Dementia in Later Life: The HUNT4 70+ Study.

BACKGROUND AND OBJECTIVES: The cognitive reserve hypothesis posits that cognitively stimulating work delays the onset of mild cognitive impairment (MCI) and dementia. However, the effect of occupational cognitive demands across midlife on the risk of these conditions is unclear. METHODS: Using a cohort study design, we evaluated the association between registry-based trajectories of occupational cognitive demands from ages 30-65 years and clinically diagnosed MCI and dementia in participants in the HUNT4 70+ Study (2017-19). Group-based trajectory modeling identified trajectories of occupational cognitive demands, measured by the routine task intensity (RTI) index (lower RTI indicates more cognitively demanding occupation) from the Occupational Information Network. Multinomial regression was implemented to estimate the relative risk ratios (RRRs) of MCI and dementia, after adjusting for age, sex, education, income, baseline hypertension, obesity, diabetes, psychiatric impairment, hearing impairment, loneliness, smoking status, and physical inactivity assessed at HUNT1-2 in 1984-1986 and 1995-1997. To handle missing data, we used inverse probability weighting to account for nonparticipation in cognitive testing and multiple imputation. RESULTS: Based on longitudinal RTI scores for 305 unique occupations, 4 RTI trajectory groups were identified (n = 7,003, 49.8% women, age range 69-104 years): low RTI (n = 1,431, 20.4%), intermediate-low RTI (n = 1,578, 22.5%), intermediate-high RTI (n = 2,601, 37.1%), and high RTI (n = 1,393, 19.9%). Participants in the high RTI group had a higher risk of MCI (RRR 1.74, 95% CI 1.41-2.14) and dementia (RRR 1.37, 95% CI 1.01-1.86), after adjusting for age, sex, and education compared with participants in the low RTI group. In a sensitivity analysis, controlling for income and baseline health-related factors, the point estimates were not appreciably changed (RRR 1.66, 95% CI 1.35-2.06 for MCI, and RRR 1.31, 95% CI 0.96-1.78 for dementia). DISCUSSION: People with a history of cognitively stimulating occupations during their 30s, 40s, 50s, and 60s had a lower risk of MCI and dementia older than 70 years, highlighting the importance of occupational cognitive stimulation during midlife for maintaining cognitive function in old age. Further research is required to pinpoint the specific occupational cognitive demands that are most advantageous for maintaining later-life cognitive function.

Trajectories of occupational physical activity and risk of later-life mild cognitive impairment and dementia: the HUNT4 70+ study.

Background: High levels of occupational physical activity (PA) have been linked to an increased risk of dementia. We assessed the association of trajectories of occupational PA at ages 33-65 with risk of dementia and mild cognitive impairment (MCI) at ages 70+. Methods: We included 7005 participants (49.8% were women, 3488/7005) from the HUNT4 70+ Study. Group-based trajectory modelling was used to identify four trajectories of occupational PA based on national registry data from 1960 to 2014: stable low (30.9%, 2162/7005), increasing then decreasing (8.9%, 625/7005), stable intermediate (25.1%, 1755/7005), and stable high (35.2%, 2463/7005). Dementia and MCI were clinically assessed in 2017-2019. We performed adjusted multinomial regression to estimate relative risk ratios (RRR) with 95% confidence intervals (CI) for dementia and MCI. Findings: 902 participants were diagnosed with dementia and 2407 were diagnosed with MCI. Absolute unadjusted risks for dementia and MCI were 8.8% (95% CI: 7.6-10.0) and 27.4% (25.5-29.3), respectively, for those with a stable low PA trajectory, 8.2% (6.0-10.4) and 33.3% (29.6-37.0) for those with increasing, then decreasing PA; while they were 16.0% (14.3-17.7) and 35% (32.8-37.2) for those with stable intermediate, and 15.4% (14.0-16.8) and 40.2% (38.3-42.1) for those with stable high PA trajectories. In the adjusted model, participants with a stable high trajectory had a higher risk of dementia (RRR 1.34, 1.04-1.73) and MCI (1.80, 1.54-2.11), whereas participants with a stable intermediate trajectory had a higher risk of MCI (1.36, 1.15-1.61) compared to the stable low trajectory. While not statistically significant, participants with increasing then decreasing occupational PA had a 24% lower risk of dementia and 18% higher risk of MCI than the stable low PA group. Interpretation: Consistently working in an occupation with intermediate or high occupational PA was linked to an increased risk of cognitive impairment, indicating the importance of developing strategies for individuals in physically demanding occupations to prevent cognitive impairment. Funding: This work was supported by the National Institutes of Health (R01AG069109-01) and the Research Council of Norway (296297, 262700, 288083).

Correlation between cognitive ability and educational attainment weakens over birth cohorts.

Educational attainment is a key indicator of status and opportunity in meritocratic societies. However, it is unclear how educational expansion has affected the link between cognitive abilities and educational attainment. As a result, this study examines the correlation between cognitive ability and educational attainment across male birth cohorts in Norway. Utilizing administrative register data covering more than four decades, we investigate multiple measures of educational attainment and their connection to cognitive abilities. Our findings reveal a consistent decline in the correlation over time. These findings question the assumed shift towards meritocracy in educational systems and highlight a more complex relationship between cognitive ability and educational attainment.

Retirement age and disability status as pathways to later-life cognitive impairment: Evidence from the Norwegian HUNT Study linked with Norwegian population registers.

BACKGROUND: Research shows that retirement age is associated with later-life cognition but has not sufficiently distinguished between retirement pathways. We examined how retirement age was associated with later-life dementia and mild cognitive impairment (MCI) for people who retired via the disability pathway (received a disability pension prior to old-age pension eligibility) and those who retired via the standard pathway. METHODS: The study sample comprised 7210 participants from the Norwegian Trøndelag Health Study (HUNT4 70+, 2017-2019) who had worked for at least one year in 1967-2019, worked until age 55+, and retired before HUNT4. Dementia and MCI were clinically assessed in HUNT4 70+ when participants were aged 69-85 years. Historical data on participants' retirement age and pathway were retrieved from population registers. We used multinomial regression to assess the dementia/MCI risk for women and men retiring via the disability pathway, or early (<67 years), on-time (age 67, old-age pension eligibility) or late (age 68+) via the standard pathway. RESULTS: In our study sample, 9.5% had dementia, 35.3% had MCI, and 28.1% retired via the disability pathway. The disability retirement group had an elevated risk of dementia compared to the on-time standard retirement group (relative risk ratio [RRR]: 1.64, 95% CI 1.14-2.37 for women, 1.70, 95% CI 1.17-2.48 for men). MCI risk was lower among men who retired late versus on-time (RRR, 0.76, 95% CI 0.61-0.95). CONCLUSION: Disability retirees should be monitored more closely, and preventive policies should be considered to minimize the dementia risk observed among this group of retirees.

Stability and change in male fertility patterns by cognitive ability across 32 birth cohorts.

The relationship between cognitive ability (CA) and childbearing remains unsettled. Using Norwegian administrative registers with population coverage, we study how male lifetime fertility patterns differ across cognitive score groups, and how these changed across the 1950-1981 birth cohorts, covering a period characterized by rapid social and economic change. The analyses reveal systematic differences in fertility and fertility timing across CA groups, with high scoring males having delayed but ultimately higher fertility than lower scoring males. This pattern remains stable over time despite strong trends towards delayed and reduced fertility. The overall positive relationship between CA and fertility is primarily driven by high rates of childlessness in the lowest scoring group, with low-scoring males showing higher rates of parity progression at higher parities.

Marital Histories and Associations With Later-Life Dementia and Mild Cognitive Impairment Risk in the HUNT4 70+ Study in Norway.

Objectives: Earlier studies suggest that being married in later life protects against dementia, and that being single in old age increases the risk of dementia. In this study, we examine midlife marital status trajectories and their association with dementia and mild cognitive impairment (MCI) at ages 70 plus using a large population based sample from Norway. Methods: Based on a general population sample linked to population registries (N = 8706), we used multinomial logistic regression to examine the associations between six types of marital trajectories (unmarried, continuously divorced, intermittently divorced, widowed, continuously married, intermittently married) between age 44 and 68 years from national registries and a clinical dementia or a MCI diagnosis after age 70. We estimated relative risk ratios (RRR) and used mediation analyses adjusting for education, number of children, smoking, hypertension, obesity, physical inactivity, diabetes, mental distress, and having no close friends in midlife. Inverse probability weighting and multiple imputations were applied. The population attributable fraction was estimated to assess the potential reduction in dementia cases due to marital histories. Results: Overall, 11.6% of the participants were diagnosed with dementia and 35.3% with MCI. Dementia prevalence was lowest among the continuously married (11.2%). Adjusting for confounders, the risk of dementia was higher for the unmarried (RRR = 1.73; 95% CI: 1.24, 2.40), continuously divorced (RRR = 1.66; 95% CI: 1.14, 2.43), and intermittently divorced (RRR = 1.50; 95% CI: 1.09, 2.06) compared to the continuously married. In general, marital trajectory was less associated with MCI than with dementia. In the counterfactual scenario, where all participants had the same risk of receiving a dementia diagnosis as the continuously married group, there would be 6.0% fewer dementia cases. Discussion: Our data confirm that staying married in midlife is associated with a lower risk of dementia and that divorced people account for a substantial share of dementia cases.

Hearing loss, sick leave, and disability pension: findings from the HUNT follow-up study.

BACKGROUND: Evidence on the association between hearing loss and sick leave or disability pension is to a great extent based on few cross-sectional studies and remains unclear. We aim to assess the associations in a long-term follow-up population study. METHODS: We used baseline data from a large population-based hearing study in Norway, the HUNT Hearing study (1996-1998). The sample included 21 754 adults (48.5% men, mean age at baseline 36.6 years). We used register data on sick leave and disability pension (1996-2011). Cox regression was used to assess the association between hearing loss at baseline (Pure tone average/PTA 0.5-4 kHz > 20 dB) and time to first physician-certified sick leave episode, as well as time to first disability pension payment. RESULTS: Hearing loss at baseline (yes/no) was weakly associated with time to first physician-certified sick leave episode: Hazard ratio (HR) 1.2 (95% confidence interval (CI) 1.1-1.3). Restricting the exposed group to people with both hearing loss and tinnitus, the HR was slightly increased: 1.3 (95% CI 1.1-1.6). Hearing loss in 1996-1998 was also associated with time to first received disability pension: HR 1.5 (95% CI 1.3-1.8). Stronger associations were found for disabling hearing loss (PTA > 35). Restricting the exposure to hearing loss and tinnitus, the HR was increased: 2.0 (95% CI 1.4-2.8). CONCLUSIONS: This large population-based cohort study indicates that hearing loss is associated with increased risk of receiving disability pension, especially among younger adults and low educated workers. Hearing loss was weakly associated with sick leave.

Technology-induced job loss risk, disability and all-cause mortality in Norway.

BACKGROUND: Ongoing shifts in economic structure from automation and globalisation can affect employment and mortality, yet these relations are not well described. OBJECTIVE: We assess whether long-term employment and health outcomes relate systematically to structural change in the labour market, using the occupational Routine Task Intensity (RTI) score as indicator of exposure is to risks of outsourcing and technology-induced job loss. METHODS: Using a cohort design and administrative data with national population coverage, we categorise all Norwegian employees in 2003 by the RTI score of their occupation and examine how this score correlates with employment and health outcomes measured in 2018 and 2019. The study sample counts 416 003 men and 376 413 women aged 33-52 in 2003. RESULTS: The occupational RTI score at baseline is robustly associated with long-term employment, disability and mortality outcomes. Raw correlations are reduced after adjustment for potential confounders, but associations remain substantial in models controlling for individual covariates and in sibling comparisons. Working in an occupation with RTI score 1 SD above the mean in 2003 is associated with a raised probability of being deceased in 2019 of 0.24 percentage points (95% CI: 0.18 to 0.30) for men and 0.13 percentage points (95% CI: 0.02 to 0.24) for women, corresponding to raised mortality rates of 6.7% and 5.5%. CONCLUSIONS: Individuals in occupations characterised by high routine intensity are less likely to remain employed in the long term, and have higher rates of disability and mortality.

Fathers of children conceived using ART have higher cognitive ability scores than fathers of naturally conceived children.

STUDY QUESTION: Does paternal cognitive ability differ for children conceived with and without assisted reproductive technology (ART)? SUMMARY ANSWER: Young fathers of ART conceived children tend to score cognitively below their same-age natural conception (NC) counterparts and older (above 35) fathers of ART conceived children tend to score above. WHAT IS KNOWN ALREADY: Cognitive ability is a genetically and socially transmitted trait, and If ART and NC children have parents with different levels of this trait, then this would in itself predict systematic differences in child cognitive outcomes. Research comparing cognitive outcomes of children with different modes of conception finds conflicting results, and studies may be influenced by selection and confounding. STUDY DESIGN, SIZE, DURATION: This is a population-based study based on Norwegian data, combining information from the Medical Birth Registry (births through 2012), military conscription tests (birth cohorts 1955-1977) and the population registry. These data allow us to compare the cognitive ability scores of men registered as the father of an ART-conceived child to the cognitive abilities of other fathers and to average scores in the paternal birth cohorts. PARTICIPANTS/MATERIALS, SETTINGS, METHODS: The population level study included 18 566 births after ART (5810 after ICSI, 12 756 after IVF), and 1 048 138 NC births. It included all Norwegian men who received a cognitive ability score after attending military conscription between 1973 and 1995. This constituted 614 827 men (89.4% of the male birth cohorts involved). An additional 77 650 unscored males were included in sensitivity analyses. MAIN RESULTS AND THE ROLE OF CHANCE: Paternal cognitive level was assessed using intelligence quotients (IQ) converted from stanine scores on a three-part cognitive ability test with items measuring numeracy, vocabulary and abstract thought (Raven-like matrices). ART fathers averaged 1.95 IQ points above the average of their own birth cohort (P-value < 0.0005) and 1.83 IQ points above NC fathers in their own birth cohort (P < 0.0005). Comparisons of the IQ of ART fathers to those of NC fathers of similar age and whose children were born in the same year, however, found average scores to be more similar (point estimate 0.24, P = 0.023). These low average differences were found to differ substantially by age of fatherhood, with young ART fathers scoring below their NC counterparts and older ART fathers scoring above their NC counterparts. LIMITATIONS, REASONS FOR CAUTION: We do not have information on maternal cognition. We also lack information on unsuccessful infertility treatments that did not result in a live birth. WIDER IMPLICATIONS OF THE FINDINGS: Paternal cognitive ability of ART children differs from that of NC children, and this difference varies systematically with paternal age at child birth. Selection effects into ART may help explain differences between ART and NC children and need to be adequately controlled for when assessing causal effects of ART treatment on child outcomes. STUDY FUNDING/COMPETING INTEREST(S): This research has also been supported by the Research Council of Norway through its Centres of Excellence funding scheme, project number 262700 (Centre for Fertility and Health). It has also been supported by the Research Council of Norway's Project 236992 (Egalitarianism under pressure? New perspectives on inequality and social cohesion). There are no competing interests. TRIAL REGISTRATION NUMBER: N/A.

Flynn effect and its reversal are both environmentally caused.

Population intelligence quotients increased throughout the 20th century-a phenomenon known as the Flynn effect-although recent years have seen a slowdown or reversal of this trend in several countries. To distinguish between the large set of proposed explanations, we categorize hypothesized causal factors by whether they accommodate the existence of within-family Flynn effects. Using administrative register data and cognitive ability scores from military conscription data covering three decades of Norwegian birth cohorts (1962-1991), we show that the observed Flynn effect, its turning point, and subsequent decline can all be fully recovered from within-family variation. The analysis controls for all factors shared by siblings and finds no evidence for prominent causal hypotheses of the decline implicating genes and environmental factors that vary between, but not within, families.