Adult testosterone levels

4.5.2.1 Aggressive behaviour

A number of studies provide evidence for an influence of circulating levels of androgens on aggression in males and females after puberty (Table 4.2). The hormonal effect is now referred to as activational as opposed to organizational effects in early life. In the beginning, several pertinent studies were carried out in prison where usually some ofthe inmates are highly aggressive. Here, the researchers expected a significant relationship between current testosterone levels and aggression, a hypothesis that was confirmed.

There is consistent data from eight studies carried out on different types of violent male offenders who showed substantially higher testosterone levels than those found in selected samples of less violent prison inmates. Kreuz and Rose (1972) were the first to find that prisoners with a history of violent crime during adolescence showed higher testosterone levels than prisoners lacking such a history. Similar positive findings were reported by Aromaki et al. (1999); Banks and Dabbs (1996); Brooks and Reddon (1996); Dabbs et al. (1987; 1991; 1995), Ehrenkranz et al. (1974) as well as by Mattsson et al. (1980) who also found in their study of adolescent offenders that verbal aggression and impulsive behaviour in prison correlated significantly positively with testosterone levels. Studies of female prison inmates (Dabbs et al. 1988; Dabbs and Hargrove 1997) confirmed the results obtained from male offenders. Even the low testosterone concentrations in women, about 10 to 15% of circulating testosterone levels in men, exerted an influence on aggression or unprovoked violence in women. These findings, however, should not lead to the conclusion that testosterone unconditionally illicits violence in humans. It can only alter the probability that aggressive behaviour will occur under a specific combination of external and internal cues. Moreover, even if many findings suggest that testosterone is related to antisocial and offending behaviour, a significant positive correlation of testosterone with violence does not correspond necessarily with a high degree of aggression in all probands of the sample. There may also be individuals with relatively low testosterone levels and a high degree of aggression in the same study group.

With less severe offences the evidence for testosterone influence on aggressive behaviour is not as consistent. Neither Meyer-Bahlburg and his co-workers (1974a; 1974b), who investigated eight men with XYY-syndrome in comparison to normal XY-males nor Lindman et al. (1992) with their study on men who had been arrested for battering their wife under alcohol influence could find significantly higher testosterone levels in the study group in comparison to their controls, in the latter case non-violent pub patrons with a similar amount of alcohol consumption.

On the other hand, aggressive behaviour which was not a punishable offence also showed significant correlations with androgens in men and women. Under experimentally controlled alcohol intake, aggressively predisposed students were more dominant in a discussion and had higher free testosterone levels than nonag-gressively predisposed students (Lindman et al. 1987). In male hockey players the pre-play testosterone levels correlated positively with reactive aggression during the tournament (Scaramella and Brown 1978). Male patients in a clinic for nervous diseases showed more destructive aggression with higher levels of testosterone (Kedenburg 1977); in female patients he also detected a positive, however insignificant relation. The latter result was confirmed by Ehlers et al. (1980) who found that female outpatients of a neurobehavioural clinic who displayed more aggressive behaviour had significantly higher testosterone levels than women who were low in aggression.

In pubescent boys peer's and mothers' ratings of aggressive behaviour correlated positively with testosterone and several other androgens (Olweus etal. 1980; 1988; Susman etal. 1987). Testosterone-aggression relations based on hormone levels and observational measures of female adolescents while interacting with their parents were significantly positive with regard to their expression of anger when aggressed against by the parents (Inoff-Germain etal. 1988).

In a group of traditionally living !Kung San hunter-gatherers (so-called bushmen) from the Kalahari desert in Namibia, Christiansen and Winkler (1992) found that within a subgroup of physically aggressive San men violent behaviour correlated significantly and positively with free testosterone and 5a-dihydrotestosterone (DHT) levels. As the physically aggressive men also exhibited higher mean values in body measurements of robustness of the face and trunk, this finding may point to a possible pathway of indirect androgen action on human aggression, in addition to the widely accepted influence of testosterone on aggressive behaviour via its action on specific sites in the central nervous system.

4.5.2.2 Sexual aggression

Many aspects of sexual behaviour in the normal male are testosterone-dependent. With pathologically low serum testosterone levels a significant decrease in the frequency of sexual fantasies, sexual arousal and desire, spontaneous nocturnal or morning erections, ejaculations, sexual activity with and without a partner has been observed and also successfully treated with androgen replacement. Even among eugonadal men, some evidence for a positive relationship of endogenous testosterone with sexual behaviour has been found. This gave rise to the supposition that abnormally high androgen levels in men might elicit rape or other types of sexual aggression.

The first pertinent study was carried out on 52 sex offenders by Rada et al. (1976). A group ofbrutally violent rapists (according to clinical classification, police records and interviews) showed significantly higher levels of plasma testosterone than a combination of three other groups consisting of less overtly violent rapists, convicted child molesters and adult male volunteers. Taken together as one subgroup, rapists (both brutal and less violent) did not differ significantly from the child molesters in testosterone levels. Their mean serum testosterone values of

6.1 ng/ml (rapists) and 5.0 ng/ml (child molesters) both fell within the range of normal populations.

In a follow-up studyRada etal. (1983) failed to confirm differences in testosterone concentrations between a subsample ofviolent rapists and non-violent sex offenders or normal controls, while the group of child molesters had significantly lower testosterone levels than the rapists' group.

In a study of healthy normal young men Christiansen and Knussmann (1987a) found that interest in sexual aggression - assessed by measuring the viewing times of relevant slides - exhibited a low positive correlation with free testosterone and a significantly negative correlation with the hormone ratio DHT to testosterone. The correlation coefficients of free testosterone levels and interest in aggressive sexuality rose slightly as the aggressiveness illustrated in the slides increased.

4.5.2.3 Self-ratings of aggression

While the positive link between testosterone and past or present aggressive behaviour is fairly consistent, self-report measures of aggression, irritability, and hostility exhibit as many insignificant as significant relations with endogenous testosterone levels. Table 4.2 gives an overview of the distribution of significant and insignificant findings over the last twenty years, both for aggressive behaviour and self-ratings of aggression.

The inconsistent results for questionnaire data may be explained by several factors. First the selection of subjects and sample size: the age of the volunteers ranged between 10 to over 70 years; the sample sizes varied between 5 and 1709 subjects. Furthermore, great differences exist with regard to the number of serum or saliva samples collected for the hormone assays. In most studies only a single sample was used to determine the individual's sex hormone level; other investigators preferred to rely on up to 30 samples collected over a two-month period in order to find the typical sex hormone level of a subject. Additional influence on the outcome of psychoendocrinological studies stems from the choice of the questionnaire. As the studies originate from countries all over the world, it was impossible always to use the same aggression inventory and thus quite diverse scales are supposed to represent the same personality trait, e.g., dominance, hostility or reactive aggression.

A positive relation of testosterone and questionnaire data of aggressiveness was found in both sexes from puberty to old age (Aromaki et al. 1999; Cashdan 2003; Christiansen and Knussmann 1987a; Ehrenkranz et al. 1974; Gladue 1991b; Gray etal. 1991; Harris etal. 1996; Houser 1979; Mattsson etal. 1980; Olweus etal. 1980; Persky et al. 1971; Rada et al. 1983; van Goozen et al. 1994a; von der Pahlen et al. 2002). Gladue (1991b) is the only one who found significantly negative correlations between testosterone and self-report measures of physical and verbal aggression in females - in contrast to the results of van Goozen et al. (1994a) and Harris et al. (1996).

Several researchers could not detect any significant testosterone-aggressiveness relationship in men or women (Bateup et al. 2002; Campbell et al. 1997; Dabbs etal. 1991; Doering etal. 1975; Kreuz and Rose 1972; Meyer-Bahlburg etal. 1974b; Monti etal. 1977; Persky etal. 1977, 1982; Rada etal. 1976; Susman etal. 1987; Udry and Talbert 1988).

Thus it seems to be worth considering whether perhaps the relationship between testosterone and aggressiveness might be obscured by the interindividual variability in environmental, familial, and cognitive characteristics as well as personality traits that promote learning and emission of aggressive behaviour.

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