Friday, March 1, 2013

What is love?

A psychoneuroendocrinological perspective on love

Leanne Fogg

What is love? I mean deep, passionate, head-over-heels love? Can’t-image-life-without-them love? What about love that never fades? Emotions are not so easily defined or measured, so the most honest answer I can provide lies within the endocrine system: hormones don’t lie.

The Endocrine System
The endocrine system includes a series of glands that release hormones (chemical messengers) into the bloodstream to elicit a response. Hormones will bind to a receptor, eventually resulting in the production of new proteins or an alteration in the activity of an existing protein. Responses can be transient or long lasting, depending on structure and composition of the hormone initiating the response. Testosterone and cortisol are some commonly known hormones that are associated with feelings of love. Other endocrine factors play roles in the emotion of love, including vasopressin, oxytocin, dopamine, serotonin, and nerve growth factor.
Scientists recognize three different stages of love: falling in love, passionate love, and companionate love. Many would agree stages were assigned appropriately, but it is difficult to umbrella the complexities of relationships into three categories – a prime example of reductionism (taking something complex and breaking it down into parts). When faced with the intricacies of love, a reductionist view can be a good place to start.

Phase 1: Falling in love 
The first stage of a relationship is often very passionate, intimate, and euphoric. Partners are generally excited, experiencing feelings of infatuation and adoration toward their new mate. Although individuals experience a lot of happiness in a new relationship, high cortisol levels indicate feelings of stress during this phase. People who claim to have fallen in love within the last 6 months had significantly higher cortisol levels than individuals not in a relationship. Stress can result from feeling insecure, fearing judgment and/or rejection. Both men and women possess great desire to impress their mate, often resulting in mood and personality changes.

Although cortisol levels are high in both genders during early love, hormonal cues are often distinct between men and women. Testosterone, known for its primary role in the development of the male reproductive system, is often elevated in males rather than in females. The male testes and female ovaries secrete testosterone, influencing behavioral aspects of social interactions, including aggression and sexual intimacy. Testosterone levels in young lovers are often low in men and high in women when compared to their respective controls (individuals currently not in a relationship). While the role of testosterone is generally linked to reproductive efforts, the discrepancy of testosterone levels between genders during early love remains unexplained.

Table 1: Hormonal changes in the early stages of love (Marazzitia, 2004)
It is believed that the elevated testosterone production in single males is a product of mating effort – the increased time and energy invested in obtaining a mate. This hormonal change could possibly be a product of the “Coolidge effect” – the fluctuation of male libido given various mate choices. Increased libido is observed when males are provided multiple females to mate with, while decreased male libido results when only given one female mate. When males “settle down” into a relationship, less energy is spent on finding a mate, resulting in decreased testosterone levels. Alternatively, males in a relationship who continue to pursue females other than their primary partner have higher levels of testosterone than loyally committed males. Also, elderly men who report high numbers of lifetime sex partners have elevated testosterone levels compared to those with less sexual encounters.

The differences in testosterone levels between genders as well as the elevated cortisol fade within 1-2 years after experiencing initial feelings of love. Eventually, testosterone levels of both male and females will decrease, and drop further throughout the progression of a relationship.

Figure 1: Male testosterone levels decrease throughout progression of a relationship (Caldwell Hooper, 2011)

Phase 2: Passionate Love
After the initial “honeymoon phase” of a relationship, feelings of security, peace, and balance take over. Partners experience “passionate love,” full of intimacy and satisfaction. As individuals become more comfortable and self-confident, decreased cortisol levels can lead to improved health benefits. These include reduced anxiety and depression as well as improved immune defense, general health, and well-being. Increased commitment and intimacy between partners often results in the formation of strong pair bonds. Oxytocin and vasopressin are nanopeptides hormones (made of nine amino acids) that facilitate the learning of personal recognition through binding receptors (mainly) in the brain. Although they play a role in forming early love connections, they continue to contribute to the strengthening of a relationship. This peptidergic signaling coincides with dopaminergic reward systems pathways, reinforcing the pair bond relationship.

Figure 2: Oxytocin (OT) and vasopressin (AVP) hormones coincide with dopaminergic signaling (DA) in the formation of strong pair bonds  (Debiec, 2007)

Phase 3: Companionate love
Some relationships can progress to a third state of “companionate love,” commonly referred to as an “empty love.” This can be a result from dwindled passion, causing commitment to be the crux of the relationship. Oxytocin and vasopression continue to promote positive, comforting feelings of the pair bond, but diminishing testosterone levels might elucidate feelings of a dull relationship. Breakups can result at this stage, unless commitment is strong enough. The “4 year itch” phenomenon is characteristic of couples not content with companionate love, often resulting in a divorce 4 years into marriage. However, some couples claim to share passionate love even after 20 years of marriage, suggesting that some relationships remain in the early stages of love.

Long Distance
Long distance relationships can be an emotional rollercoaster, influenced by changes in hormonal signaling initiated by the physical presence of a pair bond partner. Women tend to have higher levels of testosterone when their partner lives in the same city – possibly a result of consistent reproductive effort. When partners are reunited after periods of separation, testosterone levels spike, cortisol decreases, and sleep patterns are altered. The difficult whirlwind of a long distance relationship is plagued with hormonal fluctuations, often creating difficulties in maintaining a partnership.

The complex sentiment of love is not so easily defined or generally described. Most psychoneuroendocrinological studies on love have focused on heterosexual interactions, describing the hormonal changes between males and females in various situations. Love can be shared between any individuals – the chemical makeup of love is not limited to the interworking of a heterosexual relationship.

Peace, Love, and Hormones.


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  1. Awesome blog Leanne! So interesting and revealing.

    1. Thank you! I did not do justice to all physiological components involved in feelings of love, but did my best!

  2. Lovely article ! Thanks to Emily who shared this on Facebook :-)