Religious upbringing and neuroticism in Dutch twin families.

Evidence for a relation between neuroticism and religion is scarce and inconsistent. The aims of the present study were to determine the association of religious upbringing with adult neuroticism scores and to examine the effect of religious upbringing on the heritability of neuroticism. As part of a longitudinal survey of twin families from the Netherlands Twin Register, data were collected on neuroticism and religious upbringing. Restricting the sample to persons aged 25 and over resulted in a sample of 4369 twins and 1304 siblings from 2698 families. Religious upbringing was significantly associated with neuroticism; in both men and women neuroticism levels were lower in those who had received a religious upbringing. There were no sex or twin-sibling differences in neuroticism variances and covariances. Structural equation modeling showed differences in heritability between those with and without religious upbringing. In the group with religious upbringing, variation in neuroticism was determined for 41 % by additive genetic factors and for the remaining 59% by unique environmental factors. In the group who had not received a religious upbringing, variation in neuroticism was determined for 55% by genetic factors, with evidence for both additive and nonadditive factors, and for the remaining 45% by unique environmental influences. In conclusion, having received a religious upbringing is associated with lower neuroticism scores and a lower heritability in adulthood

Personality differences in monozygotic twins discordant for cannabis use.

Aims: To explore the association between cannabis and personality scores when genetic background and shared environment are controlled for. Design: The co-twin control design. This design provides a powerful method for controlling for the effects of potentially confounding familial factors that may act to predispose subjects both to cannabis use and a particular personality profile. Participants: 118 monozygotic twin pairs discordant for cannabis use. Measurements: Data on personality and cannabis use were obtained through a questionnaire survey. The Dutch Sensation Seeking List was used to assess various aspects of sensation seeking. The Amsterdamse Biografische Vragenlijst assessed extraversion, neuroticism, somatic complaints and test attitude. Findings: The affected twins scored higher on all scales than their unaffected co-twins, especially on experience seeking (P = 0.004), total sensation seeking score (P = 0.004) and neuroticism (P = 0.039). Differences were also observed when items on drug use were removed from the experience seeking scale (P = 0.037) and total sensation seeking score (P = 0.009) although these differences were no longer significant after Bonferoni correction (P < 0.005). Conclusions: Cannabis use is associated with a higher score on personality scales. This result was obtained in a sample of monozygotic twins discordant for cannabis use. Thus, at least part of the association between cannabis use and experience seeking cannot be attributed to underlying genetic or shared environmental factors that influence both personality and cannabis use and must be explained by unique environmental influences. © 2007 The Authors

Smoking status of parents, siblings and friends: Predictors of regular smoking? Findings from a longitudinal twin-family study

Item does not contain fulltextThe relationship between regular smoking behavior and the smoking behavior of parents, siblings and friends was investigated using data from the Netherlands Twin Register. Cross-sectional analyses of data of 3906 twins showed significant associations between smoking behavior of the participant and smoking behavior of co-twin, additional brothers, parents of the same sex as the participant and friends. Those variables, together with age, explained 47% of the variance in smoking behavior. Longitudinal analyses of data from 2397 twins, who, in 1993, reported never to have smoked (regularly), showed that uptake of regular smoking two years later was predicted by having a smoking co-twin, smoking same-sex siblings, smoking mother and smoking friends. Males are, in contrast to females, at a later age still vulnerable to taking up regular smoking. The variables explained 21% of the variance. Sport participation, alcohol use, boredom susceptibility and neuroticism significantly added to the predictive value of this model. Including those additional factors increased the explained variance to 30%, and subsequently adding experimental smoking behavior further increased the explained variance to almost 50%. In summary, having smoking family members and friends, as well as lifestyle and personality factors are important predictors for the uptake of regular smoking. However, the experimental smoking behavior of the participant is equally important.9 p

Cellular and mucosal immune reactions to mental and cold stress: Associations with gender and cardiovascular reactivity

To examine gender differences in immune reactions to stress and relationships between immune and cardiovascular reactivity, measures of cellular and mucosal immunity and cardiovascular activity were recorded in 77 men and 78 women at rest and in response to active (mental arithmetic) and passive (cold pressor) stress tasks. Both tasks reduced CD4+ T cells and the CD4/8 ratio. Total lymphocytes, NK cells, CD8+ T cells, and secretory immunoglobulin A (sIgA) increased with active stress. Passive stress decreased sIgA. At rest, men had more NK cells, less CD4+ T cells, and fewer neutrophils than women. Mental stress increased sIgA in men but not women. Cardiovascular reactivity to active stress was associated with increases in NK cells. The data support the hypothesis that stress-related increases in lymphocytes are beta-adrenergically mediated, and suggest that the fall in CD4+ T cells may be alpha-adrenergically driven. Mechanisms underlying sIgA reactions are more difficult to determine. Men and women differed in some cell counts, but not in reactivity, although gender influenced sIgA reactions to arithmetic

Drinking by parents, siblings, and friends as predictors of regular alcohol use in adolescents and young adults : A longitudinal twin-family study.

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Sleep during a regular week night: A twin-sibling study.

Previous genetic investigations of variation in normal sleep have focused on measures that describe sleep over longer periods of time. We undertook a study with the aim of evaluating whether heritability can be found in single-night sleep traits. A classical twin study design of monozygotic and dizygotic twins, enriched with siblings of twins was employed. The study included adult twin pairs and their siblings (N = 813 subjects from 342 families). A subsample of 66 individuals participated twice. For a single night, bedtime, awakening time and subjective sleep quality were assessed using a diary. The diary also assessed smoking, alcohol and coffee consumption, and the subjective evaluation of stress. Resemblance between family members was used to estimate the heritability of bedtime, awakening time, sleep problems and sleep quality as a function of sex. Most sleep measures showed familial clustering, but results differed for men and women. Heritability for bedtime and sleep problems was seen in women; and for awakening time in men. We conclude that heritability can be demonstrated for bedtime and subjective evaluation of even a single night of sleep. The contribution of the genetic make-up is sex specific. In women variance in awakening time is so affected by environmental circumstances, that the genetic contribution to the variance becomes negligible. In contrast, for males, variance in the evening bedtime is so affected by environmental circumstances, that the genetic contribution to the variance becomes negligible