The influence of psychosocial stress, socioeconomic differences and coffee consumption in the etiology of type 2 diabetes

Sammanfattning: Type 2 diabetes is a chronic disease of multiple etiology and with increased prevalence during the past two decades. We investigated the influence of psychosocial stress in association with type 2 diabetes and looked further into possible explanations of socioeconomic differences in diabetes risk. We also investigated coffee consumption in association with the disease. The analyses are based on data from a cross-sectional study, comprising 3128 Swedish men and 4821 women aged 35-56 years at time of examination (1992-1994 and 1996-1998, respectively). All participants went through an oral glucose tolerance test which identified 55 men and 52 women with previously undiagnosed type 2 diabetes, and 172 men and 167 women with impaired glucose tolerance (IGT). The participants also responded to a detailed questionnaire about their lifestyle. Psychosocial stress was analyzed by assessing work stress (i.e. high demands and low decision latitude at work), and sense of coherence (SOC) (a factor for successful coping with stressors). Socioeconomic position (SEP) was measured by occupational titles and to explain possible socioeconomic differences in type 2 diabetes risk we examined the impact of established risk factors (obesity, physical inactivity, smoking and family history of diabetes) and psychosocial stress (work stress and low SOC). To further examine socioeconomic differences we analyzed childhood and adolescence SEP, measured as fathers' occupational position and participants' education. We calculated odds ratios, interpreted as relative risks (RRs) along with 95% confidence intervals (Cls) by means of multiple logistic regression analyses. Our findings indicate that low decision latitude at work and low SOC were associated with type 2 diabetes in women (RR=2.2, CI:1.04.8 and RR=3.7, CI:1.2-11.2, respectively). The underlying mechanisms may involve psychosocial stress inducing insulin resistance via psychoendocrine pathways. However, high demands at work did not influence these associations. Moreover, these variables were not obviously related with type 2 diabetes in men, nor with IGT in men or in women. Middle and low SEP were associated with type 2 diabetes in both men (RR=2.4, CI: 1.0- and RR=2.9, CI:1.5-5.7, respectively) and women (RR=3.2, CI:1.5-6.6 and RR=2.7, CI:1.3-5.9, respectively) and also with IGT in women (RR=1.5, CI:1.0-2.2 and RR=1.9, CI:1.3-2.8, respectively). In women, the differences in type 2 diabetes risk were explained by both established risk factors and psychosocial stress factors (81-100%). In men, however, socioeconomic differences were partly explained by established risk factors (36-42%), whereas psychosocial stress factors had no effect. The associations between type 2 diabetes, IGT and lower (middle and low) SEP in childhood and adolescence disappeared after adjustment for adult SEP and adult factors (established risk factors and psychosocial stress factors). It may be hypothesized however, that factors associated with type 2 diabetes risk accumulate as a result of socioeconomic disadvantage over the life course. Finally, higher coffee consumption (>=3 cups of coffee per day) was inversely associated with type 2 diabetes and IGT in men and women. It has been indicated that constituents in coffee may have beneficial effects by improving insulin sensitivity and enhancing insulin response. In conclusion, the findings from this thesis suggest that psychosocial stress, at least in women, socioeconomic differences and coffee consumption play a role in type 2 diabetes etiology.