Hormonal changes when falling in love
Introduction
The formation of pair bonding is relevant in several animal species, and particularly in mammals since, in some cases, it ensures not only that a new couple is formed which can thus generate offsprings, but also that a safe and stable environment is set up wherein the newborn can receive sufficient care to enable them to mature and become capable of surviving alone (Bowlby, 1969, Kleiman, 1977, Carter et al., 1997a, Carter et al., 1997b).
The process of pair bonding in humans begins with the subjective experience of falling in love, which sometimes leads to the establishment of long-lasting relationships: for this reason, its function exceeds that of reproduction alone and, given its relevance to the survival of the species, it would not be surprising if it were regulated by precise and longstanding neural mechanisms (Uvnäs-Moberg, 1997, Uvnäs-Moberg, 1998, Carter, 1998). Indirect evidence of the biological process involved in falling in love is provided by cross-cultural studies which suggest that it is present in virtually all societies and is, perhaps, genetically-determined (Jankowiak and Fischer, 1992). Furthermore, common features of this process can be identified in studies from all over the world and include: perception of an altered mental state, intrusive thoughts and images of the other, sets of behavioural patterns aimed at eliciting a reciprocal response and a definite course and predictable outcome (Leckman and Mayes, 1999).
One of the first biological hypotheses with regard to falling in love associates this state to increased levels of phenylethylamine, on the basis of the similarities between the chemical structure of this neurotransmitter and that of amphetamines which provoke mood changes resembling those typical of the initial stage of a romance; however, no empirical data have been gathered to support this theory (Liebowitz, 1983). The strong suggestion is that different mechanisms may be involved (Panksepp, 1982, Jankoviak, 1986, Hazan and Shaver, 1987, Fisher, 1992, Porges, 1998, Insel and Young, 1997) and it has been recently demonstrated that the intrusive thoughts of the early, romantic phase of a falling in love are underlaid by a decreased functionality of the serotonin transporter (Marazziti et al., 1999).
The complexity of the process would seem, therefore, to be understood better when we consider falling in love as a basic emotion, such as anxiety or fear, due to the activation of the amygdala and related circuits and neurotransmitters (Bartels and Zeki, 2000, LeDoux, 2000). Consistent with this hypothesis is the observation that stress and threatening situations may facilitate the onset of new social bonds and intimate ties (Bowlby, 1973, Reite, 1985, Kraemer, 1992, Panksepp et al., 1994). The review of animal data is beyond the scope of this paper, however it should perhaps be noted also that stress and corticosterone have been demonstrated to promote pair bonding formation in different species (DeVries et al., 1995, DeVries et al., 1996, Hennessy, 1997, Levine et al., 1997, Mendoza and Mason, 1997). Furthermore, these elements induce the synthesis and release of neuropeptides, such as oxytocin, which are involved in the subsequent processes, including sexual and maternal behaviours and, more in general, positive social contacts, which reduce anxiety (McCarthy et al., 1992, Numan, 1994, Carter, 1998). The literature relevant to humans in this regard is meagre, albeit in agreement with animal findings and suggests that the activation of the hypothalamic-pituitary-adrenal (HPA) axis due to stressful experiences or, more in general, to arousal, may trigger the development of different kinds of social attachment, possibly also that which begins with falling in love (Milgram, 1986, Chiodera et al., 1991, Simpson and Rhole, 1994).
Given the paucity of data in this field and the unexplored questions regarding the possible role of gonadal hormones, our study aimed at evaluating the levels of some pituitary, adrenal and gonadal hormones in a homogenous group of subjects of both sexes who were in the early, romantic phase of a loving relationship, and to compare them with those of subjects who were single or were already in a long-lasting relationship.
Section snippets
Subjects
Twenty-four subjects (12 male and 12 female, mean age±SD: 27±4 years) who declared that they had recently fallen in love, were recruited from amongst residents (17) and medical students (7), by means of advertisement. They were selected according to the criteria already applied in a previous study (Marazziti et al., 1999), in particular: the relationship was required to have begun within the previous 6 months (mean±SD: 3±1 months) and at least four hours a day spent in thinking about the
Results
Table 1 shows that cortisol levels (ng/ml) were significantly higher in the subjects who had recently fallen in love, as compared with control subjects (239 ± 39 vs 168±31, p<0.001), with no difference between women and men.
The levels of LH, estradiol, progesterone, DHEAS and androstenedione did not differ between the groups and were within normal ranges according to the sex and the follicular phase of the women.
On the other hand, testosterone levels (ng/ml) in men who had recently fallen in
Discussion
The main bias of this study is probably represented by the criteria used for selecting the subjects who had fallen in love since, despite our best efforts, no definite indication was available. Since the altered mental state associated with falling in love seems to have a precise time course, with an average duration of between 18 months and 3 years (Tennov, 1979, Marazziti et al., 1999), we chose the length of the relationship as one criterion which, furthermore, can easily be recorded. The
Acknowledgements
We thank Prof. Lucia Grasso and the technical staff of the Hormone laboratory of the “Dipartimento di Endocrinologia” of the University of Pisa for performing the hormone assay. We express our gratitude to Prof. Aldo Pinchera and Prof. Enio Martino of the same Department for the fruitful discussion during the preparation of the manuscript, and to Dr. Elena Di Nasso from the “Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie” who was helpful in selecting the subjects
References (43)
Hypothalamic-pituitary-adrenal responses to brief social separation
Neur Biobehav Rev
(1997)- et al.
Preoccupations and behaviors associated with romantic and parental love. Perspectives on the origin of obsessive-compulsive disorder
Child & Adol Psychiatry Clin North Am
(1999) Inhibitory effects of oxytocin on corticotrope function in humans: are vasopressin and oxy tocin ying-yang neurohormones?
Psychoneuroendocrinol
(2001)Oxytocin may mediate the benefit of positive social interaction and emotions
Psychoneuroendocrinol
(1998)Attachment and Loss
(1969)Attachment and Loss
(1973)- et al.
The neural basis of romantic love
Neuroreport
(2000) - et al.
Peptides, steroids and pair bonding
Ann NY Acad Sci
(1997) - Carter, CS., Lederhendler, I.I., Kilpatrick, B. (eds)., 1997b. The integrative neurobiology of affiliation. Ann NY Acad...
Neuroendocrine perspectives on social attachment and love
Psychoneuroendocrinol
(1998)