Gestational thyroid hormone concentrations and risk of attention-deficit hyperactivity disorder in the Norwegian Mother, Father and Child Cohort Study.

BACKGROUND: Maternal thyroid function plays an important role in foetal brain development; however, little consensus exists regarding the relationship between normal variability in thyroid hormones and common neurodevelopmental disorders, such as attention-deficit hyperactivity disorder (ADHD). OBJECTIVE: We sought to examine the association between mid-pregnancy maternal thyroid function and risk of clinically diagnosed ADHD in offspring. METHODS: We conducted a nested case-control study in the Norwegian Mother, Father and Child Cohort Study. Among children born 2003 or later, we randomly sampled singleton ADHD cases obtained through linkage with the Norwegian Patient Registry (n = 298) and 554 controls. Concentrations of maternal triiodothyronine (T3), thyroxine (T4), T3-Uptake, thyroid-stimulating hormone (TSH) and thyroid peroxidase antibody (TPO-Ab) were measured in maternal plasma, collected at approximately 17 weeks' gestation. Indices of free T4 (FT4i) and free T3 (FT3i) were calculated. We used multivariable adjusted logistic regression to calculate odds ratios and accounted for missing covariate data using multiple imputation. We used restricted cubic splines to assess non-linear trends and provide flexible representations. We examined effect measure modification by dietary iodine and selenium intake. In sensitivity analyses, we excluded women with clinically significant thyroid disorders (n = 73). RESULTS: High maternal T3 was associated with increased risk of ADHD (5th vs 1st quintile odds ratio  2.27, 95% confidence interval 1.21, 4.26). For FT4i, both the lowest and highest quintiles were associated with an approximate 1.6-fold increase in risk of ADHD, with similar trends found for T4. The FT4i association was modified by dietary iodine intake such that the highest risk strata were confined to the low intake group. CONCLUSIONS: Both high and low concentrations of maternal thyroid hormones, although within population reference ranges, increase the risk of ADHD in offspring. Increased susceptibility may be found among women with low dietary intake of iodine and selenium.

Alcohol Consumption, HDL-Cholesterol and Incidence of Colon and Rectal Cancer: A Prospective Cohort Study Including 250,010 Participants.

AIMS: Alcohol consumption has been linked to colorectal cancer (CRC) and also to the high-density lipoprotein cholesterol level (HDL-C). HDL-C has been associated with the incidence of CRC. The aim of this study was to investigate the association between self-reported alcohol consumption, HDL-C and incidence of CRC, separately for the two sites. METHODS: Altogether, 250,010 participants in Norwegian surveys have been followed-up for an average of 18 years with respect to a first-time outcome of colon or rectal cancer. During follow-up, 3023 and 1439 colon and rectal cancers were registered. RESULTS: For men, the HR per 1 drink per day was 1.05 with 95% confidence interval (0.98-1.12) for colon and 1.08 (1.02-1.15) for rectal cancer. The corresponding figures for women were 1.03 (0.97-1.10) and 1.05 (1.00-1.10). There was a positive association between alcohol consumption and HDL-C. HDL-C was inversely associated with colon cancer in men (0.74 (0.62-0.89) per 1 mmol/l) and positively associated with rectal cancer, although not statistically significant (1.15 (0.92-1.44). A robust regression that assigned weights to each observation and exclusion of weights ≤ 0.1 increased the HRs per 1 drink per day and decreased the HR per 1 mmol/l for colon cancer. The associations with rectal cancer remained unchanged. CONCLUSION: Our results support a positive association between alcohol consumption and colon and rectal cancer, most pronounced for rectal cancer. Considering the positive relation between alcohol consumption and HDL-C, the inverse association between HDL-C and colon cancer in men remains unsettled.

The Norwegian Patient Registry and the Norwegian Registry for Primary Health Care: Research potential of two nationwide health-care registries.

In Norway, the Directorate of Health is responsible for two nationwide registries - the Norwegian Patient Registry (NPR) and the Norwegian Registry for Primary Health Care (NRPHC) - which together cover all governmental-funded health care. The NPR (specialist health care) was established in 2008, while the NRPHC (primary health care) was established in 2017. Data from the NPR are extensively used in a large variety of studies. We expect that data from the NRPHC will increase in importance when the registry covers a longer time period. The NRPHC will be especially important for studying conditions mainly treated in primary care and for investigation of patient trajectories. The main aim of this paper is to give an overview of the history and content of the NPR and its research possibilities. In addition, we introduce the NRPHC as a possible future research tool and the potential for studying patient trajectories when combining data from the two registries.

Prenatal and perinatal risk factors for eating disorders in women: A population cohort study.

OBJECTIVE: The fetal programming model hypothesizes that developmental programming in utero and in early life induces adaptations that predetermine the adult phenotype. This study investigated whether prenatal/perinatal complications are associated with lifetime eating disorders in women. METHOD: Participants included 46,373 adult women enrolled in the Norwegian Mother and Child Cohort Study (den norske Mor & barn-undersøkelsen [MoBa]). MoBa mothers and their mothers (MoBa grandmothers) were the focus of the current study. MoBa mothers with lifetime eating disorders were compared to a referent group. RESULTS: MoBa mothers who weighed more at birth (birth weight, adjusted odds ratio [OR] = 1.14; 95% confidence interval [CI]: 1.10-1.19) or were born large-for-gestational-age (adjusted OR = 1.39; 95% CI: 1.27-1.52) were more likely to develop binge-eating disorder in later life. MoBa mothers who weighed less at birth were more likely to develop anorexia nervosa (birth weight, adjusted OR = 0.88; 95% CI: 0.81-0.95). Bulimia nervosa and purging disorder (PD) were not significantly predicted by the prenatal and perinatal factors examined. DISCUSSION: Results of this study, which include the first known investigation of prenatal and perinatal factors in binge-eating disorder and PD, suggest that fetal programming may be relevant to the development of anorexia nervosa and binge-eating disorder. Future genetically informative research is needed to help disentangle whether these associations are a function of genetic influences or a true environmental fetal programming effect.

Prevalence and stability of mental disorders among young adults: findings from a longitudinal study.

BACKGROUND: Mental disorders often have onset early in life, contribute substantially to the global disease burden, and may interfere with young people's ability to complete age-relevant tasks in important developmental periods. However, knowledge about prevalence and course of mental disorders in young adulthood is sparse. The aim of the current study was to estimate prevalence and stability of mental disorders from the twenties to the thirties/forties. METHODS: DSM-IV mental disorders were assessed with the Composite International Diagnostic Interview in two waves (1999-2004 and 2010-2011) in 1623 young adult Norwegian twins (63.2% women, aged 19-29 years in wave 1). RESULTS: In wave 1, the 12-month prevalence of any mental disorder among people in the twenties was 19.8% (men) and 32.4% (women), anxiety disorders: 9.6% (men) and 26.7% (women), anxiety disorders excluding specific phobias: 2.5% (men) and 6.9% (women), major depressive disorder (MDD): 4.4% (men) and 7.2% (women), and alcohol use disorder (AUD): 8.7% (men) and 4.4% (women). The prevalence of any mental disorder decreased from the twenties to the thirties/forties. This was due to a decrease in AUD and specific phobias. Anxiety disorders in the twenties predicted anxiety disorders and MDD ten years later, even when controlling for the association between these disorders in the twenties. MDD in the twenties predicted MDD ten years later. At both ages, two-week and 12-month prevalence estimates differed markedly for MDD - indicating an episodic course. CONCLUSIONS: Common mental disorders are highly prevalent among young adults in the twenties, and somewhat less prevalent in the thirties/forties. Those who suffer from one mental disorder in the twenties are at considerably increased risk for suffering from a disorder ten years later as well. This may have significant implications for young people's ability to attain education, establish a family, and participate in occupational life.

The quality of severe mental disorder diagnoses in a national health registry as compared to research diagnoses based on structured interview.

BACKGROUND: Utilization of diagnostic information from national patient registries rests on the quality of the registered diagnoses. We aimed to investigate the agreement and consistency of diagnoses of psychotic and bipolar disorders in the Norwegian Patient Registry (NPR) compared to structured interview-based diagnoses given as part of a clinical research project. METHODS: Diagnostic data from NPR were obtained for the period 01.01.2008-31.12.2013 for all patients who had been included in the Thematically Organized Psychosis (TOP) study between 18.10.2002 and 01.09.2014 with a Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) diagnosis of schizophrenia (n = 537), delusional disorder (n = 48), schizoaffective disorder (n = 118) or bipolar disorder (n = 408). Diagnostic agreement between the primary DSM-IV diagnosis in TOP and the International Classification of Diseases, 10th revision (ICD-10) diagnoses in NPR was evaluated using Cohen's unweighted nominal kappa (κ). Diagnostic consistency was calculated as the proportion of all registered severe mental disorder diagnoses in NPR that were equivalent to the primary diagnosis given in the TOP study. RESULTS: The proportion of patients registered with the equivalent ICD-10 diagnosis as the primary DSM-IV diagnosis given in TOP was 84.2% for the schizophrenia group, 68.8% for the delusional disorder group, 76.3% for the schizoaffective disorder group, and 78.4% for the bipolar disorder group. Diagnostic agreement was good for schizophrenia (κ = 0.74) and bipolar disorder (κ = 0.72), fair for schizoaffective disorder (κ = 0.63), and poor for delusional disorder (κ = 0.39). Among patients with DSM-IV schizophrenia, 4.7% were diagnosed with ICD-10 bipolar disorder, and among patients with DSM-IV bipolar disorder, 2.5% were diagnosed with ICD-10 schizophrenia. Diagnostic consistency was 84.9% for schizophrenia, 59.1% for delusional disorder, 65.9% for schizoaffective disorder, and 91.0% for bipolar disorder. CONCLUSIONS: When compared to research-based diagnoses, clinical diagnoses of schizophrenia and bipolar disorder in the NPR are accurate and consistent, with minimal diagnostic overlap between the two disorders.

Pre-pregnancy mental distress and musculoskeletal pain and sickness absence during pregnancy - a twin cohort study.

Background: Sickness absence (SA) among pregnant women is high. The aim of this study was to examine whether factors known to predict SA in general also predict SA during pregnancy by estimating the association between prior mental distress and musculoskeletal pain and SA during pregnancy, and to assess the influence of familial (genetic and shared environmental) factors. In this prospective cohort study, data from 2076 female twins born 1967-79 who participated in a questionnaire study in 1998 were linked to register data on SA and childbirth during the years 1998-2008. Baseline measures included mental distress (symptoms of anxiety and depression; SCL-5) and musculoskeletal pain (lumbar spine, neck/shoulder and/or persisting muscular pain). SA was measured as a ratio of days on SA divided by potential working days. Negative binomial regression was performed for individual and within-pair effects. Musculoskeletal pain, but not mental distress, was prospectively associated with overall SA during pregnancy in the adjusted individual-level analyses. With each standard deviation increase in musculoskeletal pain, SA granted for any disorder increased with 12% (IRR 1.12, 95% CI = 1.07-1.17) and SA granted for pregnancy related disorders increased with 9% (IRR 1.09, 95% CI = 1.02-1.17). Within-pair estimates were similar, suggesting little or no familial confounding. Women with previous musculoskeletal pain are at increased risk of SA during pregnancy, whereas no increased risk in women with previous symptoms of mental distress could be demonstrated. SA during pregnancy seems partly to be associated with different factors than SA in general.

Mood, anxiety, and alcohol use disorders and later cause-specific sick leave in young adult employees.

BACKGROUND: Mental disorders strongly influence work capability in young adults, but it is not clear which disorders that are most strongly associated with sick leave, and which diagnoses that are stated on the sick leave certificates. Better knowledge of the impairments associated with different mental disorders is needed for optimal planning of interventions and prioritization of health services. In the current study, we investigate the prospective associations between eight mood, anxiety, and alcohol use disorders, and later sick leave granted for mental, somatic, or any disorder. METHODS: Lifetime mental disorders were assessed by structured diagnostic interviews in 2,178 young adults followed for eight years with registry data on sick leave. Relative risk ratios were estimated for the associations between each mental disorder and the different forms of sick leave. RESULTS: All included diagnoses were associated with later sick leave. In adjusted analyses, major depressive disorder and generalized anxiety disorder were the strongest predictors of sick leave granted for mental disorders, whereas social anxiety disorder and specific phobia were the strongest predictors of sick leave granted for somatic disorders. Specific phobia and major depressive disorder had the highest attributable fractions for all-cause sick leave. CONCLUSIONS: Mood and anxiety disorders constituted independent risk factors for all cause sick leave, whereas alcohol use disorders seemed to be of less importance in young adulthood. Disorders characterised by distress were most strongly associated with sick leave granted for mental disorders, whereas disorders characterised by fear primarily predicted sick leave granted for somatic conditions. A large part of all sick leave is related to specific phobia, due to the high prevalence of this disorder. The impairment associated with this common disorder may be under-acknowledged, and it could decrease work capacity among individuals with somatic disorders. This disorder has good treatment response and may be overlooked as a target for interventions aimed at prevention of sick leave.

Does low alcohol use increase the risk of sickness absence? A discordant twin study.

BACKGROUND: Results from observational studies suggest that people who drink little or no alcohol are less healthy than medium drinkers. This has been demonstrated for many different measures of health, including sick leave. However, whether these associations are causal or due to confounding remains to be clarified. The aim of this study was to use a discordant twin design to determine whether the increased level of sick leave associated with a low level of alcohol consumption, as compared to those with a medium level of consumption, reflects a causal mechanism or is due to genetic or environmental confounding. METHODS: Six thousand seven hundred thirty-four young adult twins from the Norwegian Institute of Public Health's twin panel were in 1998 assessed for frequency of alcohol use and binge drinking. Data were linked to the Norwegian National Insurance Administration's recordings of sick leave over a 10 year period. The associations between alcohol consumption and sick leave were first estimated in the total study population, and then within di- and monozygotic twin pairs discordant for alcohol use. RESULTS: Compared to medium consumption, both low and high alcohol consumption was associated with increased risk of sick leave. When low level drinkers were compared to medium level drinkers in a discordant twin design, the results were consistent with the association being due to genetic confounding rather than a causal effect. CONCLUSIONS: The increased level of sick leave observed with low level drinkers seems to be mainly explained by confounding from genetic factors. In all observational studies of the relationship between alcohol consumption and health, one should be aware that important genetic confounders are likely to influence the results.

Interaction of Apolipoprotein E Genotypes, Lifestyle Factors and Future Risk of Dementia-Related Mortality: The Cohort of Norway (CONOR).

BACKGROUND/AIMS: Our aims were two-fold: firstly, to investigate the association and interaction between apolipoprotein E (ApoE), lifestyle risk factors and dementia-related mortality and, secondly, to examine if using dementia-related mortality yielded comparable risk estimates for the ApoE genotypes as reported in studies using a clinical dementia diagnosis as the end point. METHODS: We used a nested case-control study with 561 cases drawn from dementia deaths in the Cohort of Norway (CONOR) and 584 alive controls. RESULTS: ApoE ε4 carriers were at increased risk of dementia-related mortality compared to noncarriers [odds ratio (OR) 2.46, 95% confidence interval (CI) 1.93-3.13], and ε4 homozygotes were at particularly high risk (OR 7.86, 95% CI 3.80-13.8), while the ε2 type was associated with a lower risk. The highest risk of dementia-related mortality was found among ε4 carriers with more lifestyle risk factors (ε4 carriers who were smokers, hypertensive, physically inactive and diabetics) versus ε4 noncarriers without lifestyle risk factors (OR 15.4, 95% CI 4.37-52.4). The increased risk was additive, not multiplicative. CONCLUSIONS: Ensuring a healthy lifestyle is important to be able to prevent dementia in populations at large, but especially for ε4 carriers. Using dementia mortality gives comparable results for the ApoE-dementia association as studies using clinical dementia diagnoses.

Socioeconomic status and sick leave granted for mental and somatic disorders: a prospective study of young adult twins.

BACKGROUND: Low socioeconomic status (SES), indicated by low income and education, has consistently been found to be a strong predictor of sick leave. Several possible pathways from SES to sick leave have been described in previous literature, but there are also evidence indicating that the association can be confounded by common underlying factors. This study utilizes a population-based sample of employed young adult twins to estimate (i) the degree to which education and income are prospectively related to sick leave granted for mental, somatic, and any disorder, and (ii) whether these associations are confounded by familial factors. METHODS: Registry data on educational attainment and income at age 30 and subsequent sick leave were available for 6,103 employed young adult twins, among which there were 2,024 complete twin pairs. The average follow-up time was 6.57 years. Individual-level associations and fixed effects within twin pairs were estimated. RESULTS: Low education and income were associated with sick leave granted for both mental and somatic disorders, and with sick leave granted for any disorder. Associations were attenuated within dizygotic twin pairs and reduced to non-significance within monozygotic twin pairs, suggesting influence of familial factors on the associations between SES and sick leave. CONCLUSIONS: Low SES is associated with a higher level of sick leave granted for both mental and somatic disorders among young adults, but these associations are confounded by factors that are common to co-twins. Education and income are therefore not likely to strongly affect sick leave in young adulthood.

Substance use disorders in schizophrenia, bipolar disorder, and depressive illness: a registry-based study.

PURPOSE: To compare the prevalence and pattern of comorbid substance use disorders (SUD) between patients with schizophrenia, bipolar disorder, and depressive illness. METHODS: Data on presence of alcohol use disorder (AUD) and non-alcohol drug use disorder (DUD) were retrieved from the Norwegian Patient Register for individuals born between 1950 and 1989 who in the period 2009-2013 were diagnosed with schizophrenia, bipolar disorder or depressive illness according to the 10th version of the WHO International Classification of Diseases. The prevalence of AUD only, DUD only, or both was compared between men and women across age and diagnostic groups. RESULTS: The prevalence of SUD was 25.1 % in schizophrenia (AUD: 4.6 %, DUD: 15.6 %, AUD and DUD: 4.9 %), 20.1 % in bipolar disorder (AUD: 8.1 %, DUD: 7.6 %, AUD and DUD: 4.4 %), and 10.9 % in depressive illness (AUD: 4.4 %, DUD: 4.3 %, AUD and DUD: 2.2 %). Middle-aged men with bipolar disorder had the highest prevalence of AUD (19.1 %) and young men with schizophrenia had the highest prevalence of DUD (29.6 %). Of the specific DUDs, all but sedative use disorder were more prevalent in schizophrenia than the other groups. Cannabis and stimulant use disorder was found among 8.8 and 8.9 %, respectively, of the men with schizophrenia. CONCLUSIONS: The alarmingly high prevalence of DUD among young patients with severe mental disorders should encourage preventive efforts to reduce illicit drug use in the adolescent population.

Genetic variants in loci 1p13 and 9p21 and fatal coronary heart disease in a Norwegian case-cohort study.

Single nucleotide polymorphisms (SNPs) in loci 1p13 and 9p21 have previously been found to be associated with incident coronary heart disease (CHD). This study aimed to investigate whether these SNPs show associations with fatal CHD in a population-based cohort study after adjustment for socioeconomic- and lifestyle-related CHD risk factors not commonly included in genetic association studies. Using the population-based Cohort of Norway (CONOR), a nested case-cohort study was set up and DNA from 2,953 subjects (829 cases and 2,124 non-cases) were genotyped. The association with fatal CHD was estimated for four SNPs, three from locus 1p13 and one from locus 9p21. Multivariable Cox regression was used to estimate unstratified and gender-stratified hazard ratios while adjusting for major CHD risk factors. The associations between three SNPs from locus 1p13 and non-HDL cholesterol levels were also estimated. Men homozygous for the risk alleles on rs1333049 (9p21) and rs14000 (1p13) were found to have significantly increased hazard ratios in crude and adjusted models, and the hazard ratios remained statistically significant when both genders were analyzed together. Adjustment for additional socioeconomic- and lifestyle-related CHD risk factors influenced the association estimates only slightly. No significant associations were observed between the other two SNPs in loci 1p13 (rs599839 and rs646776) and CHD mortality in either gender. Both rs599839 and rs646776 showed significant, gradual increases in non-HDL cholesterol levels with increasing number of risk alleles. This study confirms the association between 9p21 (rs1333049) and fatal CHD in a Norwegian population-based cohort. The effect was not influenced by several socioeconomic- and lifestyle-related risk factors. Our results show that 1p13 (rs14000) may also be associated with fatal CHD. SNPs at 1p13 (rs599839 and rs646776) were associated with non-HDL cholesterol levels.

Sex differences in genetic and environmental influences on educational attainment and income.

In many Western countries, women now reach educational levels comparable to men, although their income remains considerably lower. For the past decades, it has become increasingly clear that these measures of socio-economic status are influenced by genetic as well as environmental factors. Less is known about the relationship between education and income, and sex differences. The aim of this study was to explore genetic and environmental factors influencing education and income in a large cohort of young Norwegian twins, with special emphasis on gender differences. National register data on educational level and income were obtained for 7,710 twins (aged 29-41 years). Bivariate Cholesky models were applied to estimate qualitative and quantitative gender differences in genetic and environmental influences, the relative contribution of genetic and environmental factors to the correlation between education and income, and genetic correlations within and between sexes and phenotypes. The phenotypic correlation between educational level and income was 0.34 (0.32-0.39) for men and 0.45 (0.43-0.48) for women. An ACE model with both qualitative and quantitative sex differences fitted the data best. The genetic correlation between men and women (rg) was 0.66 (0.22-1.00) for educational attainment and 0.38 (0.01-0.75) for income, and between the two phenotypes 0.31 (0.08-0.52) for men and 0.72 (0.64-0.85) for women. Our results imply that, in relatively egalitarian societies with state-supported access to higher education and political awareness of gender equality, genetic factors may play an important role in explaining sex differences in the relationship between education and income.

Personality disorders and long-term sick leave: a population-based study of young adult Norwegian twins.

Personality disorders (PDs) reduce global functioning, are associated with high levels of work disability, and are thus also likely to influence long-term sick leave (LTSL). Previous research has indicated significant genetic influence on both DSM-IV PDs and LTSL. To what degree genes contributing to PDs also influence LTSL has not been investigated. The aims of the current study were to investigate which PDs were significantly associated with LTSL, to what extent the genetic contributions to these PDs account for the heritability of LTSL, and to explore the hypothesis of a causal association between PDs and LTSL. The sample consisted of 2,771 young, adult Norwegian twins, born 1967-1979. PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV). The age range for the interview was 20-32. The data were subsequently linked to public records of LTSL (sick leave >16 days) up to 11 years later. The odds ratio for being in the highest LTSL category (>15% sick leave) when fulfilling the DSM-IV criteria for any PD diagnosis was 2.6 (1.8-3.8, 95% CI). Dimensional representations of schizotypal, paranoid, and borderline PD were independently and significantly associated with LTSL. The heritability of LTSL was 0.50. Genetic factors shared with the PDs accounted for 20% of this. The association between PDs and LTSL was due to shared genetic and not environmental influences, and was mainly explained by one common genetic factor. The hypothesis of a causal association was not supported, indicating that the association is explained by overlapping genetic liability between PDs and LTSL.

Personality disorders are important risk factors for disability pensioning.

PURPOSE: To determine whether personality disorders (PDs) are associated with increased risk of disability pensioning in young adults, independent of other common mental disorders. METHODS: 2,770 young adults from the general population were assessed for PDs by the Structured Interview for DSM-IV Personality, and for common mental disorders by the Composite of International Diagnostic Interview. These data were linked to the Norwegian National Insurance Administration's recordings of disability benefits for a 10-year period. Logistic regression analyses were applied to investigate the association between PDs and disability pensioning. The analyses were conducted for three types of PD measures: categorical diagnoses (any PD), dimensional scores of individual PDs and higher order components retrieved by principal component analyses. RESULTS: Having any PD was strongly associated with disability pensioning, regardless of disability diagnosis. The estimated odds ratio (OR) was substantially higher for PDs [OR 4.69 (95% confidence interval (CI) 2.6-8.5)] than for mood disorders [OR 1.3 (CI 0.7-2.3)] and anxiety disorders [OR 2.3 (CI 1.3-4.3)]. Measured dimensionally, all PD traits except antisocial traits were significantly associated with disability pensioning. After adjusting for co-occurring traits of other PDs, only schizoid, dependent and borderline PD traits showed a significant positive association with disability pension, while antisocial traits showed a significant negative association. The principal component analyses showed that negative affectivity, psychoticism, and detachment was associated with an increased risk of disability pensioning, while antagonism/disinhibition and obsessivity were not. CONCLUSIONS: PDs are strongly associated with disability pensioning in young adults, and might be more important predictors of work disability than anxiety and depressive disorders. Certain aspects of pathologic personalities are particularly important predictors of disability.

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.