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.

Education in Twins and Their Parents Across Birth Cohorts Over 100 years: An Individual-Level Pooled Analysis of 42-Twin Cohorts.

Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990-1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.

Blood pressure in young adulthood and residential greenness in the early-life environment of twins.

BACKGROUND: Previous research shows that, besides risk factors in adult life, the early-life environment can influence blood pressure and hypertension in adults. However, the effects of residential traffic exposure and residential greenness in the early-life on blood pressure in young adulthood are currently unknown. METHODS: Ambulatory (24-h) blood pressures of 278 twins (132 pairs) of the East Flanders Prospective Twins Study were obtained at the age of 18 to 25 years. Prenatal and adulthood residential addresses were geocoded and used to assign prenatal and postnatal traffic and greenness indicators. Mixed modelling was performed to investigate blood pressure in association with greenness while adjusting for potential confounding factors. RESULTS: Night-time systolic blood pressure was inversely associated with greenness at the residential address in twins living at the same address their entire life (non-movers, n = 97, 34.9%). An interquartile increase in residential greenness exposure (1000 m radius) was associated with a 3.59 mmHg (95% CI: -6.0 to -1.23; p = 0.005) lower adult night systolic blood pressure. Among twins who were living at a different address than their birth address at time of the measurement (n = 181, 65.1%), night-time blood pressure was inversely associated with residential surrounding greenness at adult age as well as with residential greenness in early-life. However after additional adjustment for residential greenness exposure in adulthood, only residential greenness exposure in early-life was significantly associated with night systolic blood pressure. While no significant effect of adult residential greenness with adult blood pressure was observed, while accounting for the early-life greenness exposure. CONCLUSIONS: Lower residential greenness in the early-life environment was independently associated with a higher adult blood pressure. This indicates that residential greenness has persistent effects on blood pressure.

Evidence that moment-to-moment variation in positive emotions buffer genetic risk for depression: a momentary assessment twin study.

OBJECTIVE: The negative affective response to daily life stressors, which previous work suggest is a fundamental depression endophenotype, may be moderated by positive emotions. It was investigated whether positive affect (PA) buffers negative affect (NA) reactivity in response to stress and whether PA moderates the genetic predisposition to negative affect reactivity. METHOD: A total of 279 twin pairs participated in a momentary assessment study with the experience sampling method, collecting appraisals of stress and affect in the flow of daily life. Lifetime diagnoses of depression were obtained. RESULTS: There was a significant interaction between stress appraisal of event (STRESS) and PA in the association with NA. The interaction between proband PA, proband STRESS and co-twin lifetime depression showed that higher PA reduced the interaction between proband STRESS and co-twin lifetime depression. CONCLUSION: Positive emotions not only buffer against NA reactivity, but in addition attenuate genetic effects on negative mood bias in daily life.

Genes making one feel blue in the flow of daily life: a momentary assessment study of gene-stress interaction.

OBJECTIVE: Individual differences in stress reactivity constitute a crucially important mechanism of risk for depression. Because stress can be conceptualized as the continuous occurrence of minor daily hassles, this study focused on emotional reactivity to stress in the flow of daily life and examined to what degree individual differences in emotional reactivity could be explained by genetic and/or environmental factors. METHODS: Two hundred seventy-five female twin pairs (170 monozygotic and 105 dizygotic) participated in this experience sampling study (ESM). ESM is a validated structured diary technique assessing stressors and mood in daily life. Individual emotional stress reactivity was conceptualized as changes in negative affect in relation to appraised subjective stress in relation to daily events. Structural equation modeling was used to fit univariate models. The best fitting model was chosen based on likelihood and parsimony. RESULTS: Genetic factors (explaining 12% individual differences) and individual-specific environmental factors (explaining 88%) influenced daily life stress reactivity. CONCLUSION: The demonstration of a small genetic influence on the dynamic relationship between minor stress and affective response in the flow of daily life sheds light on the gene-environment interactions that contribute to the risk of developing stress related disorders such as depression.

A social component in the negative effect of sons on maternal longevity in pre-industrial humans.

Due to their effect on maternal testosterone levels, sons are said to have reduced maternal longevity in pre-industrial humans. This analysis, using information from a Flemish agricultural village in the 18th-20th centuries, confirms the presence of a negative effect of sons on maternal longevity. However, the effect is mainly observed for mothers belonging to the least privileged social group and for sons surviving their fifth birthday. Both findings make the above-mentioned biological explanation relative. However, a plausible alternative, social interpretation is male-dominated intra-household resource competition. It is reasonable to assume that only sons above a certain age are able to claim a serious amount of resources and that competition is strongest within the least privileged social group.