Summary
In order to be cost-effective, downstream information campaigns and interventions aiming to prevent T2DM must effectively target people at high risk. Hence, we analyzed which sociodemographic, socioeconomic, behavioral and clinical factors are associated with prediabetes. Furthermore, we analyzed the overlap of the three prediabetes criteria and whether the risk factors for IFG, IGT and increased HbA1c levels differed. We observed that the overlap of people defined through all three prediabetes criteria is quite small and that age, obesity, hypertension, low levels of education, unemployment, statutory health insurance, living in urban areas and physical inactivity are risk factors for prediabetes. We also found that some risk factors for the three prediabetes stages differed. For example, men are more likely to have IFG than women, whereas women are more likely to have IGT or increased HbA1c levels. Similarly, unemployment is strongly associated with IGT, but only weakly with IFG or increased HbA1c levels.
Comparison with previous studies
To our knowledge, no previous study comprehensively described the overlap of all three criteria (IGT, IFG and increased HbA1c levels) in a large European population-based sample. A recent review from Barry et al. identified only five studies that compared IGT, IFG and increased HbA1c levels in one sample but only two of those studies (one from China, one from the USA) were based on population-based samples. The pooled data of the five studies showed that the prevalence of prediabetes with ADA criteria was 54% and 8.7% of those with prediabetes fulfilled all three criteria [19]. Similarly, Saukkonen et al. reported in a small Finish sample that the overlap for HbA1c > 5.7%, IFG and IGT in people with prediabetes was quite small [27]. In that study, 34% of participants were classified as having prediabetes and only 3% of those with prediabetes fulfilled all three prediabetes criteria. With 10%, the overlap of people with prediabetes who had increased HbA1c levels, IFG and IGT in our study was comparably small. Furthermore, comparable to the study of Barry et al., the majority of people with prediabetes in our sample had IFG (67%) and increased HbA1c (51%), whereas the prevalence of IGT (32%) was much lower. That the joint distribution of IGT, IFG and increased HbA1c differs significantly between men and women with a much higher proportion of women with increased HbA1c values is a new finding that has not been reported in this way before. The reasons for this finding are unknown, but the data show that the choice of the definition for prediabetes is likely to have a large impact on the share of women and men that are having prediabetes and might be eligible for certain types of lifestyle interventions to prevent diabetes.
There are also few studies that analyzed the full range of clinical, behavioral, sociodemographic and socioeconomic factors that are associated with prediabetes. Similar to our study, a cross-sectional study based on a Spanish sample showed that the modifiable risk factors alcohol consumption, hypertension and weight and lipid status are associated with prediabetes defined through IFG or HbA1c > 5.7% [28]. Other studies found that low income and education levels or living in deprived areas are associated with the existence of T2DM, but only few investigations are available that analyze factors associated with prediabetes [29,30,31,32].
We did not find studies that explicitly compared the characteristics of people with IFG, IGT and increased HbA1c values. Measurements of fasting glucose, 2-h postprandial glucose and HbA1c have different advantages in terms of practicability and costs. Furthermore, both the transition probability from prediabetes to diabetes and the relative risk reduction that can be managed through lifestyle interventions differ between people with IGT, IFG and increased HbA1c [19, 33]. Therefore, knowledge on the risk factors of corresponding high-risk groups is highly valuable to choose the best suitable diagnostic criteria and to identify the right target groups for specific diabetes prevention approaches.
Implications for health policy
Several countries have initiated large-scale programs to promote and deliver LSM interventions, i.e., diabetes prevention programs, to individuals at high risk. Since the initiation of the National Diabetes Prevention Program in the USA, a public–private partnership to implement low-cost intervention (LCI) diabetes prevention programs in community setting, more than 240,000 people at high risk have been enrolled into one of the programs [34]. However, given that more than 80 million Americans have prediabetes, only a small fraction of at-risk individuals has received lifestyle interventions [35]. The gap in the cascade of diabetes prevention has also been highlighted in a recent analysis showing that only around a third of people with prediabetes have been told by their doctors that they are at high risk [36]. Therefore, reaching people at high risk to attend regular screening procedures and to engage in healthy lifestyle is of great importance for a successful implementation of large-scale diabetes prevention programs or efforts for high-risk individuals—particularly as targeted screening and identification of high-risk individuals are more cost-effective than universal screening [37].
One instrument to reach specific populations is media campaigns [38, 39]. Although media campaigns can potentially approach large segments of the population, even these methods can be optimized by correctly addressing the population subgroups at high risk for T2DM. In contrast, to target physician–patient communication guided by clinical variables, health media campaigns rely on data available to public health advocates such as information on sociodemographic and socioeconomic background of groups. The Federal Centre for Health Education (BZgA) in Germany recently initiated an information and communication strategy to prevent and treat T2DM [40]. The results of our study are very valuable for such national efforts. For example, our findings indicate that age is one of the strongest risk factors and prevention efforts in elderly settings will reach many high-risk individuals. Furthermore, our study shows that information campaigns aiming to raise awareness for prediabetes might be best targeted to statutorily insured people, those living in urban areas or visiting job centers, working in the blue collar industry where the proportion of university graduates is low or working in other industry sectors where physical activity levels are typically low.
Strengths and limitations
This is one of the first studies testing the associations of a broad set of sociodemographic, socioeconomic, clinical and behavioral factors with prediabetes in a large European sample. A strength of this study is its population-based design with standardized measures of FPG, 2 h-PGG and HbA1c. Furthermore, using a pragmatic health policy perspective and the use of easy-to-measure characteristics as potential predictors allow physicians and health agencies to target screening, prevention and information campaigns.
As a limitation, it needs to be acknowledged that the data we used were sampled from a relatively affluent region in Southern Germany, where people are more likely to be healthier compared to the average German population. Furthermore, due to the design of our pooled analysis of cohort data and the likelihood of selective attrition toward more healthy participants in the follow-up studies, it is likely that the prevalence of prediabetes is underestimated in our analysis. However, it is unlikely that this biased the analyzed associations. Finally, although the data come from a population-based study, the analysis sample is not fully age representative as no OGTT was performed in people < 55 years in the baseline examination.
Conclusions
Knowledge on risk factors for prediabetes is important to effectively target high-risk individuals with downstream prevention approaches. This study shows that besides clinical and behavioral factors, also easily available sociodemographic and socioeconomic data can be used to inform this process. Importantly, it should be acknowledged that the overlap in people with IGT, IFG and increased HbA1c levels is small and that these groups differ in certain characteristics.