Smoking remains associated with education after controlling for social background and genetic factors in a study of 18 twin cohorts.

We tested the causality between education and smoking using the natural experiment of discordant twin pairs allowing to optimally control for background genetic and childhood social factors. Data from 18 cohorts including 10,527 monozygotic (MZ) and same-sex dizygotic (DZ) twin pairs discordant for education and smoking were analyzed by linear fixed effects regression models. Within twin pairs, education levels were lower among the currently smoking than among the never smoking co-twins and this education difference was larger within DZ than MZ pairs. Similarly, education levels were higher among former smoking than among currently smoking co-twins, and this difference was larger within DZ pairs. Our results support the hypothesis of a causal effect of education on both current smoking status and smoking cessation. However, the even greater intra-pair differences within DZ pairs, who share only 50% of their segregating genes, provide evidence that shared genetic factors also contribute to these associations.

Flattening the quality of life curve? A prospective person-centred study from Norway amid COVID-19.

PURPOSE: We examined multidimensional, heterogeneous reactions to the COVID-19 pandemic and associated measures to provide further insights into the developmental processes of risk and adaptation. METHOD: We used three-wave questionnaire data from 8156 individuals participating in the Norwegian County Public Health Survey assessed 1-5 months before and three (June 2020) and nine (December 2020) months after the outbreak. Latent profile and latent transition analyses were used to identify latent quality of life (QoL) classes and multiform changes, their probabilities, and predictors. RESULTS: We identified five distinct QoL classes of varying proportions, namely Flourishing (i.e. 24-40%), Content (31-46%), Content-Symptomatic (8-10%), Languishing (14-20%), and Troubled (2-5%). Despite higher levels of negative affect and lower levels of life satisfaction and positive emotions, most individuals remained in their pre-pandemic QoL profiles. Yet, changes occurred for a meaningful proportion, with transition to a less favourable class more common than to a favourable. Between time 1 and 3, the flourishing and troubled groups decreased by 40% and 60%, while the content and languishing groups increased by 48% and 43%, respectively. Favourable pre-pandemic relational (marital status, support, interpersonal trust, and belonging), health, and economy-related status predicted significantly lower odds of belonging to the high-risk groups both pre-pandemic and during the pandemic. CONCLUSIONS: Overall, this study shows lower levels of QoL amid the COVID-19 pandemic, but substantial stability in the QoL distribution, and an overall levelling of the QoL distribution. Our findings also underscore the importance of financial, health-related, and social capital to QoL.

Locked and lonely? A longitudinal assessment of loneliness before and during the COVID-19 pandemic in Norway.

AIMS: There are concerns that lockdown measures taken during the current COVID-19 pandemic lead to a rise in loneliness, especially in vulnerable groups. We explore trends in loneliness before and during the pandemic and differences across population subgroups. METHODS: Data were collected via online questionnaires in June 2020 and four to eight months prior in two Norwegian counties (N=10,740; 54% women; age 19-92 years). Baseline data come from the Norwegian Counties Public Health Survey (participation rate 46%, of which 59% took part in a COVID-19 follow-up study). RESULTS: Overall loneliness was stable or falling during the lockdown. However, some subgroups, single individuals and older women, reported slightly increased loneliness during lockdown. Interestingly, individuals with low social support and high levels of psychological distress and loneliness before the pandemic experienced decreasing loneliness during the pandemic. CONCLUSIONS: Although data limitations preclude strong conclusions, our findings suggest that, overall, Norwegians seem to have managed the lockdown without alarming increases in loneliness. It is important to provide support and to continue investigating the psychological impact of the pandemic over time and across regions differentially affected by the pandemic.

Genetic and environmental variation in educational attainment: an individual-based analysis of 28 twin cohorts.

We investigated the heritability of educational attainment and how it differed between birth cohorts and cultural-geographic regions. A classical twin design was applied to pooled data from 28 cohorts representing 16 countries and including 193,518 twins with information on educational attainment at 25 years of age or older. Genetic factors explained the major part of individual differences in educational attainment (heritability: a2 = 0.43; 0.41-0.44), but also environmental variation shared by co-twins was substantial (c2 = 0.31; 0.30-0.33). The proportions of educational variation explained by genetic and shared environmental factors did not differ between Europe, North America and Australia, and East Asia. When restricted to twins 30 years or older to confirm finalized education, the heritability was higher in the older cohorts born in 1900-1949 (a2 = 0.44; 0.41-0.46) than in the later cohorts born in 1950-1989 (a2 = 0.38; 0.36-0.40), with a corresponding lower influence of common environmental factors (c2 = 0.31; 0.29-0.33 and c2 = 0.34; 0.32-0.36, respectively). In conclusion, both genetic and environmental factors shared by co-twins have an important influence on individual differences in educational attainment. The effect of genetic factors on educational attainment has decreased from the cohorts born before to those born after the 1950s.

How should recruitment to public health surveys be conducted? / Hvordan bør rekrutteringen til folkehelseundersøkelsene gjennomføres?

BACKGROUND: The aim of the public health survey in the Norwegian counties is to obtain information that is useful for public health work. In 2018, two parallel data collection processes were undertaken in Hordaland county. Both samples were drawn randomly from the National Population Register, but one of these was limited to users of the helsenorge.no website. The purpose of this article is to investigate the degree to which limiting users to the helsenorge.no website leads to selection bias beyond the selection that occurs through ordinary non-participation. MATERIAL AND METHOD: Services for Sensitive Data (TSD) was used in the data collection for the sample drawn from the National Population Register (n = 36 000), and the helsenorge.no platform was used in the data collection for the sample limited to users of helsenorge.no (n = 30 000). The response rate was 40.8 % and 41.5 %, respectively. RESULTS: For some outcome measures, the differences between the two datasets were modest (gender distribution, age, education and health habits). For variables that were more directly related to health, the differences were greater. In the helsenorge.no sample a higher proportion reported generally poorer health (29.4 vs. 24.0 %), mental health problems (13.6 vs. 11.6 %), disability pension (10.5 vs. 7.8 %) and long-term illness (13.3 vs. 9.3 %). Analyses of subgroups showed more pronounced differences in the proportion with generally poorer health and mental health problems between those with low education in the helsenorge.no sample and the corresponding group in the sample from the National Population Register. INTERPRETATION: Systematic and pronounced differences between the samples show that limiting recruitment to users of helsenorge.no's services results in further selection problems.

Cancer Incidence and Mortality in 260,000 Nordic Twins With 30,000 Prospective Cancers.

The Nordic countries have comprehensive, population-based health and medical registries linkable on individually unique personal identity codes, enabling complete long-term follow-up. The aims of this study were to describe the NorTwinCan cohort established in 2010 and assess whether the cancer mortality and incidence rates among Nordic twins are similar to those in the general population. We analyzed approximately 260,000 same-sexed twins in the nationwide twin registers in Denmark, Finland, Norway and Sweden. Cancer incidence was determined using follow-up through the national cancer registries. We estimated standardized incidence (SIR) and mortality (SMR) ratios with 95% confidence intervals (CI) across country, age, period, follow-up time, sex and zygosity. More than 30,000 malignant neoplasms have occurred among the twins through 2010. Mortality rates among twins were slightly lower than in the general population (SMR 0.96; CI 95% [0.95, 0.97]), but this depends on information about zygosity. Twins have slightly lower cancer incidence rates than the general population, with SIRs of 0.97 (95% CI [0.96, 0.99]) in men and 0.96 (95% CI [0.94, 0.97]) in women. Testicular cancer occurs more often among male twins than singletons (SIR 1.15; 95% CI [1.02, 1.30]), while cancers of the kidney (SIR 0.82; 95% CI [0.76, 0.89]), lung (SIR 0.89; 95% CI [0.85, 0.92]) and colon (SIR 0.90; 95% CI [0.87, 0.94]) occur less often in twins than in the background population. Our findings indicate that the risk of cancer among twins is so similar to the general population that cancer risk factors and estimates of heritability derived from the Nordic twin registers are generalizable to the background populations.

Association between birth weight and educational attainment: an individual-based pooled analysis of nine twin cohorts.

BACKGROUND: There is evidence that birth weight is positively associated with education, but it remains unclear whether this association is explained by familial environmental factors, genetic factors or the intrauterine environment. We analysed the association between birth weight and educational years within twin pairs, which controls for genetic factors and the environment shared between co-twins. METHODS: The data were derived from nine twin cohorts in eight countries including 6116 complete twin pairs. The association between birth weight and educational attainment was analysed both between individuals and within pairs using linear regression analyses. RESULTS: In between-individual analyses, birth weight was not associated with educational years. Within-pairs analyses revealed positive but modest associations for some sex, zygosity and birth year groups. The greatest association was found in dizygotic (DZ) men (0.65 educational years/kg birth weight, p=0.006); smaller effects of 0.3 educational years/kg birth weight were found within monozygotic (MZ) twins of both sexes and opposite-sex DZ twins. The magnitude of the associations differed by birth year in MZ women and opposite-sex DZ twins, showing a positive association in the 1915-1959 birth cohort but no association in the 1960-1984 birth cohort. CONCLUSION: Although associations are weak and somewhat inconsistent, our results suggest that intrauterine environment may play a role when explaining the association between birth weight and educational attainment.

Genetic and environmental factors affecting birth size variation: a pooled individual-based analysis of secular trends and global geographical differences using 26 twin cohorts.

Background: The genetic architecture of birth size may differ geographically and over time. We examined differences in the genetic and environmental contributions to birthweight, length and ponderal index (PI) across geographical-cultural regions (Europe, North America and Australia, and East Asia) and across birth cohorts, and how gestational age modifies these effects. Methods: Data from 26 twin cohorts in 16 countries including 57 613 monozygotic and dizygotic twin pairs were pooled. Genetic and environmental variations of birth size were estimated using genetic structural equation modelling. Results: The variance of birthweight and length was predominantly explained by shared environmental factors, whereas the variance of PI was explained both by shared and unique environmental factors. Genetic variance contributing to birth size was small. Adjusting for gestational age decreased the proportions of shared environmental variance and increased the propositions of unique environmental variance. Genetic variance was similar in the geographical-cultural regions, but shared environmental variance was smaller in East Asia than in Europe and North America and Australia. The total variance and shared environmental variance of birth length and PI were greater from the birth cohort 1990-99 onwards compared with the birth cohorts from 1970-79 to 1980-89. Conclusions: The contribution of genetic factors to birth size is smaller than that of shared environmental factors, which is partly explained by gestational age. Shared environmental variances of birth length and PI were greater in the latest birth cohorts and differed also across geographical-cultural regions. Shared environmental factors are important when explaining differences in the variation of birth size globally and over time.

Validity of Self-Reported Birth Weight: Results from a Norwegian Twin Sample.

The association between birth weight and later life outcomes is of considerable interest in life-course epidemiology. Research often relies on self-reported measures of birth weight, and its validity is consequently of importance. We assessed agreement between self-reported birth weight and official birth records for Norwegian twins born 1967-1974. The intraclass correlation between self-reported birth weight and register-based birth weight was 0.91 in our final sample of 363 twins. It could be expected that 95% of self-reported birth-weight values will deviate from official records within a maximum of +446 grams and a minimum of -478 grams - around a mean deviation of 16 grams. Self-reported birth weight had a sensitivity of 0.78-0.89 and a positive predictive value of 0.59-0.85, and an overall weighted kappa of 0.71. We further assessed agreement by conducting two linear regression models where we respectively regressed self-reported birth weight and register-based birth weight on adult body mass index, a known association. The two models were not significantly different; however, there were different levels of significance in parameter estimates that warrant some caution in using self-reported birth weight. Reliability of self-reported birth weight was also assessed, based on self-reports in another sample of twins born 1935-1960 who had reported their birth weight in two questionnaires 34 years apart. The intraclass correlation was 0.86, which indicates a high degree of reliability. In conclusion, self-reported birth weight, depending on context and age when birth weight was reported, can be cautiously used.

The Norwegian Twin Registry from a public health perspective: a research update.

We describe the importance of the Norwegian Twin Registry (NTR) for research in public health and provide examples from several programs of twin research at the Norwegian Institute of Public Health (NIPH), including the Nordic Twin Study of Cancer, our epigenetics platform, and our large program of research in mental health. The NTR has become an integral component of a national strategy for maximizing the research potential from Norwegian registries and biobank-based studies. The information provided herein builds upon and complements our recent report describing the establishment of the NTR and the cohorts comprising it. Although Norway has a long tradition in twin research, the centralization and administration of the twin data through a single register structure is fairly recent. The NTR was established in 2009 and currently includes 47,989 twins covering birth years 1895-1960 and 1967-1979; 31,440 of these twins have consented to participate in medical research (comprising 5,439 monozygotic pairs, 6,702 dizygotic same-sexed pairs, and 1,655 dizygotic opposite-sexed pairs). DNA from approximately 4,800 twins is banked at the NIPH biobank and new studies continuously add new data to the registry. The value of NTR data is greatly enhanced through record linkage possibilities offered by Norway's many nation-wide registries (medical, demographic, and socio-economic) and several studies are already taking advantage of these linkage opportunities for research.

The Norwegian Twin Registry.

Norway has a long-standing tradition in twin research, but the data collected in several population-based twin studies were not coordinated centrally or easily accessible to the scientific community. In 2009, the Norwegian Twin Registry was established at the Norwegian Institute of Public Health (NIPH) in Oslo with the purpose of creating a single research resource for Norwegian twin data. As of today, the Norwegian Twin Registry contains 47,989 twins covering birth years 1895-1960 and 1967-1979; 31,440 of these twins consented to participate in health-related research. In addition, DNA from approximately 4,800 of the twins is banked at the NIPH biobank and new studies are continually adding new data to the registry. The value of the Norwegian twin data is greatly enhanced by the linkage opportunities offered by Norway's many nationwide registries, spanning a broad array of medical, demographic, and socioeconomic information.