LIBIDO AND AGING
HUSSEIN GHANEM M.D.
Professor of Andrology
Cairo University
Fellowship in Male Reproductive Medicine
& Surgery
University of Iowa, USA
· INTRODUCTION
· EPIDEMIOLOGY OF GERIATRIC EFFECTS
· NORMAL
PHYSIOLOGY AND AGING
Central Nervous System control on libido
Hormonal changes with age
Neurotransmitter changes with age
Vascular changes with age
Biologic factors of aging
The sexual response cycle and aging
· LIBIDO
CHANGES WITH AGING
The psychosexual theories of development
Changes in sexual drive with age
· DISORDERS
OF LIBIDO
Disorders of sexual desire
Physical and psychological factors affecting libido
Hyperlibido
· MANAGEMENT
Patient evaluation
Treatment
· REFERENCES
LIBIDO AND AGING
INTRODUCTION
The aging process is a normal developmental experience rather than a disease state. Individuals 65 or older comprise 11% of the population of the United States. Although many older individuals have illnesses which limit their functioning, a significant number of individuals over 65 are in good health and are able to enjoy a broad spectrum of recreational, social, and career pursuits(Eisdorfer, 1981). This phase of the life cycle, however is frequently complicated by physical, psychological, and social difficulties. Recognition of compromised physical, psychological, or social functioning in the elderly individuals is essential in the understanding of changes in libido(Cohen, 1981).
Libido is defined as the psychic drive or energy associated with sexual desire. Libido changes are thus related only to desire phase disorders which are different from impotence which is the inability to obtain or to maintain an erection of sufficient quality for intermission, pelvic thrusting and subsequent orgasm and ejaculation (Kaplan, 1983).
Sexual desire can be influenced in elderly men by a number of factors such as hormonal abnormalities, socio-cultural conditions, chronic diseases and drugs. Testosterone decrease per se is not sufficient to impair sexual function in the elderly. Psychological factors are also important. Drugs usually associated with impairment of libido (psychotropic drugs and antihypertensives) are frequently used by elderly people. Alcohol is a leading cause of sexual dysfunction, particularly under unfavorable social conditions (Quadri and Fronzo, 1993).
Aging in men is associated with three categories of conditions that are popularly assumed to be causally interrelated but in fact can exist independently: Erectile dysfunction, decreased androgen levels, and emotional changes. Inhibited sexual desire may be secondary to organic erectile dysfunction (McCarthy, 1992). low testosterone levels decreases the interest in sex, impairs the feeling of well being, and depresses mood. Emotional changes associated with aging include a heightened sense of mortality, a general loss in energy, and concerns about virility, career, and relationships. This triad of conditions have been termed “the male menopause” but many researches consider this to be a very broad and ill-defined term (Swerdloff and Wang, 1993).
Sexual interest and activity persist but decline through adulthood and older age. The peak of sexual activity occurs before the age of 30 and gradually diminish. Changes in sexual desire or drive becomes most noticeable Between 46 and 55 years of age. The extent depends on earlier levels of sexual interests and activity (Tsitouras et al, 1982; Hseuh, 1988).
Emotional intimacy, touching, caressing, and hugging are all very important to the well-being of the elderly. Although the libido and the capacity for sexual function decreases with age, sexuality continues to be important (Kaplan, 1983).
EPIDEMIOLOGY OF GERIATRIC EFFECTS
Sexual activity changes with age but it doesn't necessary stop. Two thirds of men maintain a good level of libido into their sixties, But erectile dysfunction may be the real problem (Verwoedt, 1969; Weitzman and Heart, 1987). Women generally report more substantial decline in sexual interest than men in these later years (Frank et al, 1978). This decrease in libido in women consistently correlates to impaired vaginal lubrication. Ovarian involution in postmenopausal women will result in depressed estrogen levels and consequently impaired libido as well as decreased vaginal lubrication (Osborn et al, 1988).
In an interesting study of sexuality in 427 aging veterans researches documented that libido is preserved, although less intense up to the age of 99. Most men in the age group of 30 -39 years rated themselves as very interested or extremely interested in sex. The mean frequency of sexual activity was once per week according to this study in this age group. Vaginal intercourse was consistently the preferred sexual activity. Most men in the age group of 90 - 99 years rated themselves as slightly interested in sex. However the mean frequency of sexual intercourse fell to once per year in this age group. The investigators concluded that based upon these findings, further research is needed to resolve this gap between intact libido and diminished potency in elderly men (Mulligan and Moss, 1991). Interestingly, Masters and Johnson (1970), reported a higher mean coital frequency of 2 times per week at the age group of 30-40 years that declined gradually to reach once per month above the age of 75 years. This difference might be related to a difference in the population sampled or perhaps a different or busier lifestyle since these studies were conducted about 20 years apart.
In a large scale population study of 1290 men - The Massachusetts Male Aging Study - investigators found that all degrees of desire phase disorders and sexual dysfunctions were more prevalent with increasing age. As expected, such disorders were increased in frequency in the presence of certain diseases. Diabetes was the most significant disorder impairing sexual activity (50%). Other significant factors decreasing sexual capacity include; heart disease, hypertension, peptic ulcer, arthritis, and cigarette smoking. It was also estimated that in the USA, 18 million men in the age group 40 - 70 are sexually dysfunctional, with the majority hesitant to seek medical advice or uninformed about the availability of treatment (Feldman et al, 1994).
NORMAL PHYSIOLOGY AND AGING
CENTRAL NERVOUS SYSTEM CONTROL ON LIBIDO
Central nervous system control on sexual function arises from both cortical and subcortical centers. Much of the knowledge about these centers is derived from the study of primates, which have presumed parallels in the mechanisms of human sexual behaviour (Rivard, 1982).
The limbic system appears to be the primary center regulating the sexual drive. It consists of portions of the cortex surrounding the upper brain stem (the hippocampus, cingulate and parahipocampal gyri) and several subcortical nuclei including the amygdala, and parts of the thalamus and basal ganglia. In addition to regulating the sexual drive and function, the limbic system is also concerned with basic physiologic drives, emotion, and the integration of sensory and visual functions (Siroky, 1979; Gibbons ,1991).
The limbic system receives external sexual stimuli in the form of tactile, visual, auditory, and olfactory afferents. Internal stimuli in the form of psychic cortical input are also integrated here. Following processing of relevant stimuli, erectile centers, located mainly in the preoptic hypothalamic area send efferent signals to the penis via the autonomic nervous system (Gibbons ,1991).
The efferent pathways courses via the median forebrain bundle to the substantia nigra through the ventrolateral pons and descends in the lateral columns of the spinal cord to sympathetic and parasympathetic effector neurons in the thoracolumber and sacral segments of the spinal cord (Saper et al, 1976).
The role of fantasy in sexual arousal makes it clear that psychic phenomena play important roles in libido and sexual behavior. Patients with damage to the sacral parasympathetic centers controlling erection can still develop erections in response to cortical imaginative stimuli as well as auditory, olfactory, and visual stimuli (MacLean and Ploog, 1962; Gibbons ,1991).
Physical and mental distractions as well as decreased testosterone levels can also play an inhibitory role on the limbic system. In aging individuals decreased hormonal levels and the presence of physical ailments can decrease libido (Pirke and Kockett, 1982).
Stimuli For Sexual Arousal
Arousal is usually initiated by means of erotic central cortical stimulation through thinking, seeing, hearing, smelling or touching sexually stimulating objects. However, the sexual response and the erection are maintained through a reflex mechanism. The sensory (afferent) limb of this reflex is through stimulating the dorsal nerve of the penis and other sensory divisions of the pudendal nerve. The motor (efferent) limb is a parasympathetic response involving sacral segments S2,3,4. Efferent neurons pass along the pelvic nerves to relay in the parasympathetic ganglia within the walls of the pelvic viscera, and reach the corpora cavernosa and cavernosal arteries through the cavernosal nerves (Horn and Zasler, 1990; Gibbons, 1991).
Ejaculation on the other hand is a combined response consisting of: Emission into the posterior urethra, bladder neck closure (sympathetic T12,L1,2,3), and ejaculation proper (sympathetic + somatic) (Strasberg and Brady, 1988).
The vascular response to parasympathetic nerve stimulation include: Cavernosal artery dilatation; sinusoidal relaxation in the corpora cavernosa; and passive venous occlusion due to compression of intersinusoidal, subtunical and emissary veins between the expanding blood sinusoids and the tunica albuginea, the tough covering of the corpora cavernosa (Lue, 1986)
It should be noted that drastic vascular changes occur also in the female during sexual excitation. Blood flow increases in the female genital organs. Increased vaginal blood flow leads to a transudate lubricating the sexual act (Hoon et al, 1981).
HORMONAL CHANGES WITH AGE
Female
The Libido in the females is not strongly tied to the testosterone production as in males. However, the sex drive decreases gradually with aging. The rate of testosterone secretion in postmenopausal women is only slightly decreased than that evident in premenopausal women, but this androgen appears to be secreted in the ovarian stroma rather then in the follicle, in response to elevated lutenizing hormone levels. The production of adrenal androgens decreases with age. The production of testosterone from all sources in postmenopausal women is about half that seen in the premenopausal women, but the drop in estrogen production is much more substantial. Consequently, the estrogen to androgen ratio declines in the postmenopausal women, and androgen effects may become more evident (Verwoerdt, 1969, Mulligan and Katz, 1988).
male
The testicular production of hormones decreases gradually with age. Total and free plasma testosterone levels fall progressively, although not necessary substantially, and gonadotropin production by the hypothalamic-pituitary axis increases. Compounding the falling levels of serum testosterone levels is the increased binding of testosterone by plasma proteins , leading to reduced androgen availability (Morley et al, 1987; Swerdolf and Wang, 1993).
These changes in hormone levels occur in parallel with decreasing sexual activity, erectile function, and libido. Plasma prolactin levels often increases slightly with age. Some correlation between the falling testosterone levels, rising prolactin levels, and decreasing sexual function has been observed elderly men (Morley et al, 1987; Swerdolf and Wang, 1993).
Hypogonadism does not usually occur in elderly men but there is a gradual decline in serum testosterone after the third decade of life. Libido is at some point of life testosterone related, and so falling androgen levels is expected to decrease libido. It is not yet settled whether dihydrotestosterone or free testosterone itself is responsible for maintaining libido (Cunningham and Hirshkowitz, 1995; Mantzoros et al, 1995).
Recent studies of androgen replacement therapy have provided some answers to the apparent contradiction between data suggesting that erection is androgen dependent and claims of erectile capacity in castrates. Hypogonadal men receiving androgen replacement therapy experienced a return of libido, mood elevation, and restored ejaculation. It appears that the physiologic decrease in androgen production with aging effects sexual desire much more than it affects potency. Although the importance of androgens for the maintenance of sexual desire and activity has been established, the amount required for basal and optimum function is not yet well defined and appears to be quite variable from one person to another (Cunningham and Hirshkowitz, 1995; Mantzoros et al, 1995).
The primary site of testosterone action in controlling sexual activity appears to be the anterior hypothalamic and preoptic area in the brain. The primary effect of this area is exerted on libido, as the erectile and ejaculatory reflex mechanisms remain intact after this area is damaged (Siroky, 1979; Gibbons ,1991).
The decreased androgen levels characteristic of old age have been related to a primary testicular defect. Evidence of this includes a decrease in Leydig cell mass and number, an increase in plasma gonadotropin levels and a decrease in Leydig cell response to human chorionic gonadotropin stimulation. These primary testicular changes may be due to impaired testicular perfusion (McClure, 1988).
There also appears to be secondary defect at the hypothalamic-pituitary level. The circadian rhythm of plasma testosterone largely disappears in elderly men. The sensitivity to sex hormone feedback also decreases. There is a significant decrease in LH and FSH response to GnRH testing. This decreased pituitary function with aging may be related to the relatively increased levels of estrogens, which would tend to inhibit gonadotropin secretion despite decreased levels of testosterone. There may also be changes in the central ‘gonadostat’ mechanism mediating hypothalamic sensitivity to estradiol feedback that alter the response to lowered testosterone levels (McClure, 1988).
NEUROTRANSMITTER CHANGES WITH AGE
Neurotransmitters and their receptors undergo a variety of changes with aging. These include generally increased serum levels of norepinephrine and decreasing sensitivity of beta adrenergic receptors in a variety of tissues. Alpha- adrenergic receptors become dominant as a consequence of this decline in beta receptor function, an alteration that interferes with vascular response of the penis that is necessary for effective tumescence (Mulligan and Katz, 1988).
VASCULAR CHANGES WITH AGE
Compounding the changes in receptor sensitivity are structural changes in the penile vasculature that make it less complaint and more occluded. Hypertension, Diabetes mellitus, smoking and hyperlipedemias may lead to accelerated atherosclerosis and arteriogenic impotence (Virag et al, 1985, Shabsigh et al, 1991; Azadozi and Goldstein, 1992). Venous function changes with age as well, partly because the rigidity of the tunica albuginea decreases thus decreasing the compression of the emissary veins passing through them. Decreased elasticity of cavenous tissue sinusoids leads to less expansion and less compression on the intersinusoidal, subtunical and emissary veins (Fournier, 1987).
BIOLOGIC FACTORS OF AGING
Puberty encompasses the biologic changes that occur in early adolescence. These changes include genital enlargement and growth pubic of pubic and axillary hair. Girls also experience breast development and menarche. Semen production begins in boys. Puberty usually occurs between 10 and 12 years of age in girls and between 12 and 14 years of age in boys. Although they are biologically based, these changes have profound psychological consequences (Greydanus et al, 1985).
Early or young adulthood is the period from 20 to 30 years. During this period the body reaches its physical, reproductive, and cognitive peaks. Adult development is less concerned with the acquisition of new capacities than with the application of these available capacities (Kaplan, 1983, Greydanus et al 1985).
Middle adulthood describes the period from 30 to 65 years of age. The aging process shapes the psychological development of middle adulthood. Aspects of illness and death emerge as inescapable facets of life during this phase of the life cycle (Osborn et al, 1988; Mulligan and Moss, 1991).
Menopause occurs between 40 and 53 years, marking the end of the reproductive years. Ovarian function is lost and menstruation ceases. Symptoms include irregular bleeding, vasomotor imbalances (hot flushes), and sweats, with decreases in estrogen secretion and changes in organic and metabolic functions. Menopause is a biologic event but the most common events are psychological. Women confronted with the end of their reproductive lives, may experience anxiety, depression, and decrease in libido as they appraise their lives and examine their choices (Osborn et al, 1988; Mulligan and Moss, 1991).
Some authors have used the terms ‘Andropause’ or ‘Male Climacteric’ but men have no specific biologic equivalent to menopause. Hormone levels in men decrease only slightly during middle adulthood. Muscle strength and endurance can be preserved with regular exercise (Swerdloff and Wang, 1993).
Later adulthood and old age begin at the age of 65 years. Gradually diminishing physical and cognitive capacities combine with the increased likelihood of acute and chronic illness as individuals enter late adulthood. The rate of decline varies significantly (Osborn et al, 1988; Mulligan and Moss, 1991; Swerdloff and Wang, 1993).
Physical changes occurring with aging are influenced by many factors (e.g., genetics, nutrition, environmental conditions). Loss of tissue elasticity is most commonly manifested by wrinkling of the skin. Postural changes are also related to loss of tissue elasticity and bone mass. Deficits in auditory and visual capacities are common because of neural and non-neural changes. Individuals compensate to these losses to various degrees(Cohen, 1981; Eisdorfer, 1981).
Cognitive capacities (e.g., recall, learning new information) may be diminished. However, Individuals with high levels of intelligence who maintain their social and intellectual activities may not experience an appreciable loss in mental capacity. Cognitive decline may be effected by level of intelligence, lack of motivation, disuse, or disease, but not necessary by diminished brain function (Cohen, 1981; Eisdorfer, 1981).
During this period a general decline in physical function occurs, but physical incapacitation is not an inevitable consequence of aging (Kaiser et al, 1988; Feldman et al, 1994).
THE SEXUAL RESPONSE CYCLE AND AGING
Masters and Johnson (1970), described four phases of physiologic changes that occur in the sexual response cycle. Helen Kaplan (1983), stressed that these phases are preceded by an appetitive or desire phase before physiologic changes are observed.
· The desire phase is characterized by the biologic need for sexual activity (the sex drive), the interest expressed in sexual activity and sex seeking and sex facilitating behavior. The intensity of sexual desire is variable among individuals and within the same individual across time and age (Helen Kaplan, 1983).
· The excitement phase is characterized by penile erection and testes elevation in the males, and clitoral enlargement, ballooning of vaginal vault and vaginal lubrication (transudate) in the females. Nipples become erect and more sensitive in both sexes.
· Plateau is full sexual excitement during intercourse. This is indicated by retraction of the clitoris against the symphysis pubis, Bartholin’s gland secretion, and formation of the orgasmic platform in females; Increase in penile circumference, increase in testicular size, and cowper’s gland secretion in males. The sexual flush could be noted during this stage in either sex.
· Orgasm is highly pleasurable sensation associated with ejaculation in the male and rhythmic contraction of pelvic floor muscles in the female. The clitoris is the most important sensory organ for female orgasm.
· Resolution: Relief of sexual excitement & relaxation after orgasm. Resolution is rapid in males and gradual in females.
· The sexual response cycle is followed by a refractory period where the person can not respond to further sexual stimuli. A full erection or a repeat orgasm is not possible during this period.
With aging, sexual responsiveness is affected by both biologic and emotional factors. Physiologic changes include delay in attaining an erection and decline in the rigidity or fullness of the erection. Men in their forties need a longer period of stimulation as well as direct stimulation to the genitals to obtain a full erection. The force of the ejaculation and the volume of the ejaculate decrease. This could be related to the altered function of various male genital glands, pelvic floor and sphincteric muscles or hypoactive sexual desire. Ejaculatory control frequently improves, but the desire for ejaculation may decrease. Resolution is quick and the erection is lost more rapidly with age. The refractory period prolongs from a few minutes in the twenties to a few days in the seventies. (Masters and Johnson, 1970; Mulligan and Katz, 1988).
In women, the onset of menopause with the associated decrease in estrogen levels results in various changes in the estrogen dependent tissues in the breast, vagina, uterus, the labia majora and minora, and the clitoris. Women may also have emotional symptoms such as mood lability and depression resulting in a hypoactive sexual desire. Vaginal lubrication usually decreases, and the vaginal vault expands less with sexual arousal. The orgasmic phase becomes shorter. Uterine contractions may become spastic and sometimes painful. The resolution phase is also more rapid (Masters and Johnson, 1970; Mulligan and Katz, 1988).