High levels of education are associated with an increased risk of latent autoimmune diabetes in adults: results from the Nord-Trøndelag health study

Association of mitochondrial DNA copy number with prevalent and incident type 2 diabetes in women: A population-based follow-up study

Mitochondrial dysfunction is an important factor of the aging process and may play a key role in various diseases. Mitochondrial DNA copy number (mtDNA-CN) is an indirect measure of mitochondrial dysfunction and is associated with type 2 diabetes mellitus (T2DM); however, whether mtDNA-CN can predict the risk of developing T2DM is not well-known. We quantified absolute mtDNA-CN in both prevalent and incident T2DM by well-optimized droplet digital PCR (ddPCR) method in a population-based follow-up study of middle aged (50-59 years) Swedish women (n = 2387). The median follow-up period was 17 years. Compared to those who were free of T2DM, mtDNA-CN was significantly lower in both prevalent T2DM and in women who developed T2DM during the follow-up period. Mitochondrial DNA-copy number was also associated with glucose intolerance, systolic blood pressure, smoking status and education. In multivariable Cox regression analysis, lower baseline mtDNA-CN was prospectively associated with a higher risk of T2DM, independent of age, BMI, education, smoking status and physical activity. Moreover, interaction term analysis showed that smoking increased the effect of low mtDNA-CN at baseline on the risk of incident T2DM. Mitochondrial DNA-copy number may be a risk factor of T2DM in women. The clinical usefulness of mtDNA-CN to predict the future risk of T2DM warrants further investigation.

The educational gradient in premature cardiovascular mortality: Examining mediation by risk factors in cohorts born in the 1930s, 1940s and 1950s

Aims

Educational inequality in cardiovascular disease and in modifiable risk factors changes over time and between birth cohorts. We aimed to assess how cardiovascular disease risk factors mediate educational differences in premature cardiovascular disease mortality and how this varies over birth cohorts and sex.

Methods

We followed 360,008 40–45-year-olds born in the 1930s, 1940s or 1950s from Norwegian health examination surveys (1974–1997) for premature cardiovascular disease mortality. Cox proportional hazard and Aalen’s additive survival analyses provided hazard ratios and rate differences of excess deaths in participants with basic versus tertiary education.

Results

Relative educational differences in premature cardiovascular disease mortality were stable, whereas absolute differences narrowed from the 1930s to the 1950s cohorts; rate differences per 100 000 person years declined from 170 (95% confidence interval 117, 224) to 49 (36, 61) in men and from 60 (34, 85) to 23 (16, 29) in women. Cardiovascular disease risk factors attenuated rate differences by 69% in both cohorts in men, and in women by 102% in 1930s and 61% in 1950s cohorts. Smoking had the single strongest influence on the educational differences for men in all three cohorts, and for women in the two most recent cohorts.

Conclusion

Smoking appeared to be the driving force behind educational differences in premature cardiovascular disease mortality in the 1930s to 1950s birth cohorts for men and in the two recent birth cohorts for women. This suggests that strategies for smoking prevention and cessation might have the strongest impact for reducing educational inequality in premature cardiovascular disease mortality.

Environmental (Lifestyle) Risk Factors for LADA

BACKGROUND

In order to prevent diabetes it is important to identify common, modifiable risk factors in the population. Such knowledge is extensive for type 2 diabetes but limited for autoimmune forms of diabetes.

OBJECTIVE

This review aims at summarizing the limited literature on potential environmental (lifestyle) risk factors for LADA.

METHODS

A PubMed search identified 15 papers estimating the risk of LADA in relation to lifestyle. These were based on data from two population-based studies; one Swedish case-control study and one Norwegian cohort study.

RESULTS

Studies published to date indicate that the risk of LADA is associated with factors promoting insulin resistance and type 2 diabetes such as overweight, physical inactivity, smoking, low birth weight, sweetened beverage intake and moderate alcohol consumption (protective). Findings also indicate potential effects on autoimmunity exerted by intake of coffee (harmful) and fatty fish (protective). This supports the concept of LADA as being a hybrid form of diabetes with an etiology including factors associated with both insulin resistance and autoimmunity.

CONCLUSION

LADA may in part be preventable through the same lifestyle modifications as type 2 diabetes including weight loss, physical activity and smoking cessation. However, current knowledge is hampered by the small number of studies and the fact that they exclusively are based on Scandinavian populations. There is a great need for additional studies exploring the role of lifestyle factors in the development of LADA.

Trace elements in early phase type 2 diabetes mellitus-A population-based study. The HUNT study in Norway

Differences in trace elements levels between individuals with type 2 diabetes and controls have been reported in several studies in various body fluids and tissues, but results have been inconsistent. In order to examine trace element levels in the early phase of type 2 diabetes, we investigated the association between whole blood levels of 26 trace elements and the prevalence of previously undiagnosed, screening-detected type 2 diabetes. The study was conducted as a case-control study nested within the third survey of the population-based Nord-Trøndelag Health Study (HUNT3 Survey). Among participants without previously known diabetes, 128 cases of type 2 diabetes were diagnosed in people with a high diabetes risk score (FINDRISC≥15), and frequency-matched for age and sex with 755 controls. Blood samples were analyzed by high resolution inductively coupled plasma mass spectrometry. Associations between trace element levels and the prevalence of previously undiagnosed type 2 diabetes were evaluated with multivariable conditional logistic regression controlling for age, sex, body mass index, waist-to-hip ratio, education, income, smoking and family history of diabetes. The prevalence of previously undiagnosed type 2 diabetes increased across tertiles/quartiles for cadmium, chromium, iron, nickel, silver and zinc, and decreased with increasing quartiles of bromine (P_trend<0.05). After corrections for multiple testing, associations for chromium remained significant (Q_trend<0.05), while associations for iron and silver were borderline significant. No associations were found for arsenic, boron, calcium, cesium, copper, gallium, gold, indium, lead, magnesium, manganese, mercury, molybdenum, rubidium, selenium, strontium, tantalum, thallium and tin. Our results suggest a possible role of bromine, cadmium, chromium, iron, nickel, silver and zinc in the development of type 2 diabetes.

Autoimmune diabetes in adults and risk of myocardial infarction: the HUNT study in Norway

BACKGROUND

The long-term consequences of autoimmune diabetes in adults (AIDA) are largely unexplored.

OBJECTIVE

To investigate the risk of myocardial infarction (MI) in AIDA compared to type 2 diabetes, taking into consideration the effects of socio-economic and lifestyle factors, the metabolic syndrome and glycaemic control.

METHODS

A total of 62 995 participants including 207 individuals with AIDA (onset ≥35 years and anti-GAD positive) and 2322 individuals with type 2 diabetes (onset ≥35 years and anti-GAD negative), from the population-based Norwegian HUNT study, were followed for a first MI during the period 1995-2008. We identified 2614 MIs by hospital records or the National Cause of Death Registry. Cox proportional hazard models were used to estimate the risk of MI by diabetes subgroups after adjustment for age and socio-economic and lifestyle factors.

RESULTS

AIDA amongst women was associated with a nearly fourfold increased risk of MI [hazard ratio (HR) 3.63, 95% confidence interval (CI) 2.21-5.96) compared to nondiabetic participants, whereas no excess risk was found in men with AIDA (HR 1.30, 95% CI 0.70-2.52). By contrast, type 2 diabetes was associated with an increased MI risk in both men (HR 1.92, 95% CI 1.62-2.26) and women (HR 2.39, 95% CI 1.98-2.89). The metabolic profile was more favourable in patients with AIDA than in those with type 2 diabetes, but glycaemic control was worse. Multivariable models and sensitivity analyses suggest that these results were robust.

CONCLUSIONS

Women with AIDA were more likely to develop MI, compared to men with AIDA and both men and women with type 2 diabetes. Further investigations are warranted to confirm this gender difference.

Incidence of type 1 diabetes in age groups above 15 years: facts, hypothesis and prospects for future epidemiologic research

Although onset of type 1 diabetes can occur in adulthood, epidemiological data are scarce, limiting our potential to identify unknown determinants of the disease. Paucity of registries expanding the recruitment of incident cases up to adulthood, atypical clinical features of type 1 diabetes at onset, misclassification of type 1 as type 2 diabetes and little use of markers of β-cell autoimmunity represents major obstacles in studying the risk of type 1 diabetes in adults. New strategies in study design, data collection and analyses may overcome these problems in the future. Population-based surveys and registries including adulthood; use of etiological rather than clinical criteria to define type 1 diabetes; availability of electronic health records as prescription data sources to avoid missing data; and application of proper statistical methods will be instrumental to gain better insight on the epidemiology and natural history of the disease.

Smoking and the Risk of LADA: Results From a Swedish Population-Based Case-Control Study

OBJECTIVE

Smoking is an established risk factor for type 2 diabetes. In contrast, it has been proposed that smoking may reduce the risk of latent autoimmune diabetes in adults (LADA), but studies are scarce. We aimed to study the impact of smoking on LADA and type 2 diabetes risks.

RESEARCH DESIGN AND METHODS

We used data from a Swedish case-control study including incident case patients with LADA (GAD antibody [GADA] positive, n = 377) and type 2 diabetes (GADA negative, n = 1,188) and control subjects randomly selected from the population (n = 1,472). We calculated odds ratios (ORs) with 95% CIs by logistic regression, adjusted for age, sex, BMI, family history of diabetes, and alcohol consumption.

RESULTS

There was no indication of reduced risk of LADA in smokers; instead, heavy smoking was associated with an increased risk of LADA (OR 1.37, 95% CI 1.02-1.84). Heavy smokers had higher levels of HOMA of insulin resistance (9.89 vs. 4.38, P = 0.0479) and HOMA of β-cell function (55.7 vs. 42.5, P = 0.0204), but lower levels of GADA (75 vs. 250, P = 0.0445), compared with never smokers. Smokers also displayed an increased risk of type 2 diabetes (OR in ever smokers 1.53, 95% CI 1.25-1.88).

CONCLUSIONS

In this large population of LADA patients, we did not observe a protective effect of smoking on autoimmunity and the risk of LADA. A protective effect could possibly be masked by a smoking-induced aggravation of insulin resistance, akin to the diabetogenic effect seen in individuals with type 2 diabetes.

No increase in new users of blood glucose-lowering drugs in Norway 2006-2011: a nationwide prescription database study

BACKGROUND

National estimates for the occurrence of diabetes are difficult to obtain, particularly time trends in incidence. The aim was to describe time trends in prevalent and incident use of blood glucose-lowering drugs by age group and gender in Norway during 2005-2011.

METHODS

Data were obtained from the nationwide Norwegian Prescription Database. We defined prevalent users of "insulins only" as individuals having no oral antidiabetic drugs (OAD) dispensed from a pharmacy during the previous 24 months or in the subsequent 12 months. Incident users had no blood glucose-lowering drugs dispensed in the previous 24 months; incident "insulins only" users also had no OAD in the subsequent 12 months.

RESULTS

In 2011, 3.2% of the population had blood glucose-lowering drugs dispensed, and the incidence rate was 313 per 100,000 person years. The prevalence of OAD use increased from 1.8% in 2005 to 2.4% in 2011; however a decreasing trend in incidence of OAD use was observed, particularly in those aged 70 years and older. In 2010, 0.64% of the population had insulins only dispensed, with an overall incidence rate in the total population of 33 per 100,000 person years which was stable over time.

CONCLUSIONS

In this nationwide study, we found that although the prevalent use of OAD had increased in recent years, incident use was stable or had decreased. This may indicate that the increase in diabetes occurrence in Norway is levelling off, at least temporarily.

Mortality in adult-onset autoimmune diabetes is associated with poor glycemic control: results from the HUNT Study

OBJECTIVE

Knowledge on mortality in autoimmune diabetes with adult onset is limited. We compared mortality in adult-onset autoimmune diabetes and type 2 diabetes, taking into account metabolic risk factors, HbA1c, lifestyle, and socioeconomic factors.

RESEARCH DESIGN AND METHODS

Participants of the population-based HUNT2 Study (second survey of the Norwegian HelseUndersøkelsen i Nord-Trøndelag Study; n = 64,264) were followed up prospectively for mortality in the Cause of Death Registry (1995-2009). Diabetes with onset ≥35 years was classified as autoimmune diabetes in adults if anti-GAD was positive (n = 208) and as type 2 diabetes if anti-GAD was negative (n = 2,425). Hazard ratios (HRs) of mortality from all-causes, cardiovascular disease (CVD), and ischemic heart disease (IHD) were calculated using the Cox proportional hazards model.

RESULTS

Prevalence of the metabolic syndrome was lower in autoimmune diabetes than in type 2 diabetes (55 vs. 77%, P < 0.001). Still, autoimmune diabetes was associated with an increased risks of mortality from all-causes (HR 1.55 [95% CI 1.25-1.92]), CVD (1.87 [1.40-2.48]), and IHD (2.39 [1.57-3.64]), equally high as in type 2 diabetes in analyses where individuals without diabetes were used as the reference group. The increased risk was not explained by overweight, lifestyle, socioeconomic position, or presence of the metabolic syndrome. Excess mortality was primarily observed in individuals with elevated HbA1c.

CONCLUSIONS

Mortality in autoimmune diabetes was as high as in type 2 diabetes, despite a more favorable baseline metabolic risk profile. Excess risk was associated with poor glycemic control. The results from this study, the largest so far on mortality in autoimmune diabetes in adults, underscore the importance of optimal treatment modalities to improve survival in adult-onset autoimmune diabetes.

Early life socioeconomic indicators and risk of type 1 diabetes in children and young adults

OBJECTIVE

To examine the potential role of 2 early-life socioeconomic indicators, parental education, and crowding index, on risk of type 1 diabetes (T1DM) in patients up to age 29 years to test heterogeneity by age at onset according to the hygiene hypothesis.

STUDY DESIGN

The study base was 330 950 individuals born from 1967 to 2006 who resided in the city of Turin at any time between 1984 and 2007. Data on their early life socioeconomic position were derived from the Turin Longitudinal Study; 414 incident cases of T1DM up to age 29 years were derived from the Turin T1DM registry.

RESULTS

Socioeconomic indicators had opposing effects on risk of T1DM in different age at onset subgroups. In a Poisson regression model that included both socioeconomic indicators, there was a 3-fold greater risk of T1DM (relative risk 2.91, 95% CI 0.99-8.56) in children age 0-3 years at diagnosis living in crowded houses. In the 4- to 14-year subgroup, a low parental educational level had a protective effect (relative risk 0.50, 95% CI 0.29-0.84), and the effect of crowding nearly disappeared. In the 15- to 29-year subgroup, neither crowding nor parental educational level was clearly associated with the incidence of T1DM.

CONCLUSIONS

We provide evidence of heterogeneity by age at onset of the association between early-life socioeconomic indicators and the risk of T1DM. This finding is consistent with the hypothesis that infectious agents in the perinatal period may increase the risk, whereas in the following years they may become protective factors (hygiene hypothesis).

Alcohol consumption is associated with reduced risk of Type 2 diabetes and autoimmune diabetes in adults: results from the Nord-Trøndelag health study

AIMS

We investigated the influence of different aspects of alcohol consumption on the risk of Type 2 diabetes and autoimmune diabetes in adults.

METHODS

We used data from the Nord-Trøndelag Health Survey (HUNT) study, in which all adults aged ≥ 20 years from Nord-Trondelag County were invited to participate in three surveys in 1984-1986, 1995-1997 and 2006-2008. Patients with diabetes were identified using self-reports, and participants with onset age ≥ 35 years were classified as having Type 2 diabetes if they were negative for anti-glutamic acid decarboxylase (n = 1841) and as having autoimmune diabetes if they were positive for anti-glutamic acid decarboxylase (n = 140). Hazard ratios of amount and frequency of alcohol use, alcoholic beverage choice, and binge drinking and alcohol use disorders were estimated.

RESULTS

Moderate alcohol consumption (adjusted for confounders) was associated with a reduced risk of Type 2 diabetes in men, but not in women (hazard ratio for men 10-15 g/day 0.48, 95% CI 0.28-0.77; hazard ratio for women ≥ 10 g/day 0.81, 95% CI 0.33-1.96). The reduced risk was primarily linked to consumption of wine [hazard ratio 0.93, 95% CI 0.87-0.99 (per g/day)]. No increased risk was seen in participants reporting binge drinking or in problem drinkers. The results were also compatible with a reduced risk of autoimmune diabetes associated with alcohol consumption [hazard ratio 0.70, 95% CI 0.45-1.08 (frequent consumption) and hazard ratio 0.36, 95% CI 0.13-0.97 (2-7 g/day)].

CONCLUSIONS

Moderate alcohol consumption associates with reduced risk of both Type 2 diabetes and autoimmune diabetes. A protective effect of alcohol intake may be limited to men. High alcohol consumption does not seem to carry an increased risk of diabetes.

Sleep disturbances and low psychological well-being are associated with an increased risk of autoimmune diabetes in adults. Results from the Nord-Trøndelag Health Study

AIMS

To investigate whether sleep disturbances and low psychological well-being are associated with an increased risk of autoimmune diabetes in adults (including LADA and type 1 diabetes) and type 2 diabetes.

METHODS

We used data from the Norwegian HUNT Study (n = 53,394) and estimated the risk of developing autoimmune diabetes in adults (n = 138) and type 2 diabetes (n = 1895) between 1984 and 2008 in relation to baseline self-reported psychological well-being and sleep problems.

RESULTS

Sleep disturbances and low psychological well-being were associated with an increased risk of autoimmune diabetes (hazard ratio 1.84, 95% confidence interval 1.10-3.09), primarily linked to poor sleep in men (1.83, 1.05-3.20) and low well-being in women (2.50, 1.03-6.54). Similar associations were seen with type 2 diabetes in relation to sleep problems (1.25, 1.08-1.44) in men and low well-being (1.34, 1.16-1.54), in both men and women. In autoimmune diabetes, these factors were associated with lower anti-GAD levels (177 vs. 306 WHO units/ml, p = 0.04).

CONCLUSIONS

Our findings indicate that psychosocial factors influence the risk of autoimmune diabetes in adults, possibly through mechanisms related to insulin resistance. This supports the notion that the aetiology of autoimmune diabetes with adult onset in some respects is similar to that of type 2 diabetes.

No effect by the common gene variant rs10830963 of the melatonin receptor 1B on the association between sleep disturbances and type 2 diabetes: results from the Nord-Trøndelag Health Study

AIMS/HYPOTHESIS

Genetic variation in the melatonin receptor 1B (MTNR1B) is associated with type 2 diabetes. Melatonin contributes to the regulation of sleep, and sleep problems are a documented risk factor for type 2 diabetes. The aim of this study was to investigate whether the MTNR1B gene variant rs10830963 is associated with sleep problems and whether this variant contributes to the association between sleep disturbances and type 2 diabetes.

METHODS

This was a case-control study nested within the population-based Nord-Trøndelag Health Study, including 1,322 prevalent cases of type 2 diabetes and 1,447 controls. In addition, prospective data were available for 838 incident cases and 1,133 controls. Genotyping was done by TaqMan single-nucleotide polymorphism allelic discrimination analysis. ORs and 95% CIs were calculated using logistic regression models.

RESULTS

Our findings confirm an association between sleep disturbances and type 2 diabetes (OR 1.69, 95% CI 1.22-2.33, p = 0.0016) and between the risk allele of rs10830963 and type 2 diabetes (OR 1.12, 95% CI 1.00-1.27, p = 0.0579). There was a tendency for an association between the risk allele and prevalence of sleep problems (specifically early awakening). However, the risk allele did not influence the association of sleep problems with diabetes, which was unaltered after adjustment for the MTNR1B risk allele (OR 1.69, 95% CI 1.23-2.34, p = 0.0014). Results based on prospective data were similar, although non-significant.

CONCLUSIONS/INTERPRETATION

Our findings do not support participation of the MTNR1B gene variant rs10830963 in the well documented association between sleep disturbances and type 2 diabetes.