Epidemiology of FSD
The epidemiology of female sexual dysfunction is not well understood for many reasons. Unbiased prevalence estimates from population-based samples have been rare, and incidence estimates have been nonexistent. Most published prevalence estimates have been based on selected clinical or volunteer samples. Until the recently convened “International Consensus Development Conference on Female Sexual Dysfunction” (1), where an interdisciplinary consensus conference panel, consisting of 19 experts in female sexual dysfunction selected from 5 countries expanded female sexual dysfunctions to include both psychogenic and organic causes of desire, arousal, orgasm and sexual pain disorders, there has been a contemporary lack of standard uniformly applied definitions of FSD. Thus, there has been difficulty in measuring FSD in non-clinical samples.
Accurate estimates of prevalence and incidence are important in understanding the burden of female sexual dysfunction in the community and in identifying risk factors for prevention efforts. Recognizing the distinction between prevalence and incidence is important, as each measure contains different information. Incidence is defined as the number of new cases of a condition or disease that occur during a specific time period in a population that is at risk for developing the condition. Because incidence measures the transition from a non-affected (or non-diseased) to an affected state, it is a measure of risk. Prevalence measures the number of persons affected with the condition in the population at a given point in time, but does not determine when the condition developed. Because the prevalence estimate contains persons who have had the condition for different lengths of time, it is not a measure of risk. Incidence estimates are useful for the identification of etiologic, or causal factors and for monitoring the efficacy of prevention programs. Prevalence measures are useful for estimating the burden of a particular condition on a community. Such information is valuable for planning appropriate health services for treatment and prevention efforts. Although suspected risk factors are often evaluated in relation to the prevalence of a condition, cause can only be determined using incidence.
Most published studies of the prevalence of sexual dysfunctions in women were performed in clinic or other selected samples. An excellent review of earlier studies published prior to 1988 was written by Spector and Carey. From this review it is apparent that the prevalence of most sexual dysfunctions is higher in clinical than in community samples. For instance, inhibited female orgasm ranged from 18% to 76% in clinics, but only 5% to 20% in community samples. Similarly up to 62% of females seeking sex therapy experience arousal disorder, while community estimates are closer to 11%.
There are recent studies of general or specialty clinics or selected community samples. Use of different measures and time frames for symptoms makes comparison of outcomes difficult among studies. Sample sizes varied widely from 43 women in a premenstrual syndrome clinic to 887 consecutive gynecology outpatients. Those studies less likely to suffer from selection bias are the studies by Schien with a wide age range, racial minority representation, and a detailed questonniare; Rosen with a wide age range of healthy women recruited from a wellness center; and Read with patients recruited from a general practice in the UK where 98% of the population is registered with a GP. The overall prevalence of dysfunction was reported by three studies, and ranged from 19% to 42%. The lower estimate is based on a study that asked only two brief questions about sexual functioning without probing further as to the specific type of problem. Dyspareunia was experienced by about 12% of women in two studies, and 33% in a third. The higher estimate was from a study with a high non-response rate and subjects were prior participants in a study of sexually transmitted diseases, so may be an unrepresentative sample. Problems with orgasm ranged from 5% to 23%.
There are studies regarding the prevalence of FSD from published population-based studies throughout the world. Although most studies included samples of men and women, only the results for women are presented here. Some strengths and limitations of each study are discussed below. The best information is from the large, well-designed National Health and Social Life Survey (NHSLS). This was a true population-based study of a representative sample of US adults ages 18-59. Particular strengths of the study are its large sample size, minority representation (African Americans and Hispanics), excellent response rates, inclusion of a number of detailed measures of sexuality, and many other variables pertaining to demographic, health, social, and psychological characteristics. A few limitations of the study should also be noted. These include the cross-sectional design preventing measurement of incidence, inability to measure cause and effect of related factors, or risk, the inability to examine sexual dysfunction in women aged 60 and older, and the lack of adjustment for menopause status. The NHSLS found a high overall prevalence of FSD (43%) in US women ages 18-59. Low desire was reported by 22%, arousal problems by 14% and sexual pain by 7% using categories similar to the DSM-IV defined by latent class analysis. A prior publication from the same study reported unadjusted frequencies of individual sexual dysfunction variables. About a third of women ages 18-59 reported a lack of interest in sex during the past 12 months, and a quarter of women with a partner were unable to achieve orgasm. The prevalence of dyspareunia among women with partners was 15.5%, and trouble lubricating was experienced by about 21%. In general sexual dysfunction was more common among younger women; the one exception was trouble with lubrication.
Estimates of dysfunction from an older population (> 60 years) is provided by a probability sample of adults in Michigan. Two thirds of 448 women were sexually inactive, 12% of married women had difficulty with intercourse and about 13% experienced pain with intercourse. Activity was strongly related to marital status, with only 5.3% of non-married women being sexually active. Additional limited information from women 60 years and older is reported by Marsiglio and Donnelly. In cross-sectional study of a representative sample of the US population, 49 percent of women reported no sexual activity in the past month. Women were less likely to have sex if they were older, if their partner was of poor health, and if they had low feelings of self-worth. It should be pointed out that lack of activity does not imply sexual dysfunction for older women. As shown by these two studies and others, lack of a partner or limitations of a partner are important reasons for lack of activity. Neither of these studies of older women included specific measures sexual dysfunction.
Studies were performed in middle-aged women. The overall prevalence of sexual dysfunction was estimated at 33% in the UK and 22% in Iceland. Interestingly, although a third of the women in the UK had at least one operationally defined sexual dysfunction, only 10% of them thought that they had a sexual problem. If few women perceive sexual dysfunction to be a problem, it may explain in part only a portion of women seek medical attention for these conditions.
Population estimates of inhibited desire are 22% in the US and 16% in Iceland. Almost a third of mid-life women in Australia reported decreased sexual interest, related in part to the menopausal transition, and 17% of women ages 35-59 in the UK reported impaired interest. The prevalence of dyspareunia was fairly consistent across studies, ranging from 7% to 13%, except for the Icelandic study that reported a 3.1% prevalence of functional dyspareunia. Orgasmic difficulties were reported by 3.5% of Icelandic women, 10% of Massachusetts women and 16% of women in the UK. A rigorous comparison of outcomes is difficult because of the different outcomes studied and the different ways in which they were measured.
Risk Factors for Female Sexual Dysfunction
Limited published information is available concerning risk factors for sexual dysfunction in women. The most thorough information is from the NHSLF study, although due to the cross-sectional nature of the data, the factors identified cannot be expressed truly as risk, but as correlates of dysfunction. In contrast to men, age is inversely associated with dysfunction in women. Younger age was a significant predictor for pain during sex, lack of pleasure, and anxiety about performance. Women with a lower level of education were also more likely to experience pain during sex. Low desire was more likely among women who had ever experienced a sexually transmitted disease, those reporting emotional problems or stress, women with more than a 20% drop in household income from 1988-1991, and those with infrequent thoughts about sex. Arousal disorder was higher among women with a urinary tract symptom, emotional problems or stress, infrequent thoughts about sex, and a history of being sexually touched before puberty and sexually forced by a man ever. Sexual pain was increased in women with a urinary tract symptom, and emotional problems or stress, and among those reporting poor to fair health, and a 20% decrease in household income. Low physical and emotional satisfaction and low general happiness were significant correlates of all three sexual dysfunction categories: low desire, arousal disorder and sexual pain. The Melbourne Women’s Midlife Health Study reported that a decline in sexual interest among mid-aged women was significantly related to the natural menopause transition, decreased wellbeing, decreasing employment, and increased vasomotor, cardio-pulmonary and skeletal symptoms and hormone therapy use. Unpublished cross-sectional results from the Massachusetts Women’s Health Study II indicate decreased sexual desire among married women, those with psychological symptoms, current cigarette smokers, and perimenopause status. Frequency of sexual intercourse was inversely related to depression, physical limitations of a partner, and smoking, but unrelated to menopause status. Pain during intercourse was related to recent vaginal dryness and recent urinary tract infection. No statistically significant correlates were found for difficulty reaching orgasm. Preliminary longitudinal results from the MWHS II examining a change in sexual functioning over about a six-year time period, in which women transitioned from pre- or perimenopause to postmenopause, indicate that decreased desire is related to increased age, increased body mass and poorer self-perceived health and higher desire to starting hormone therapy use.
The study of groups of women with chronic medical conditions can also provide some clues as to etiology for various sexual dysfunctions. Studies of sexual dysfunction in women with diabetes, although far from being conclusive, suggest an increased prevalence of problems such as decreased lubrication and libido that may be related to duration of diabetes and presence of neuropathy. Although treatment with antihypertensive agents has been associated with sexual dysfunction in men, there is little comparable research in women. One study has shown a disproportionate frequency of sexual dysfunction among black and Mexican-American women who had both diabetes and hypertension. There is some evidence that decreased libido and difficulties with orgasm may be related to antidepressant use in women. More research is needed concerning the relation of medications and comorbidities on the occurrence of sexual dysfunction in women.
In conclusion, female sexual dysfunction is common condition, with population estimates ranging from 22% to 43%. Population estimates of the prevalence of dyspareunia, a sexual dysfunction that causes many women to seek medical attention, ranges from 3% to 15%; estimates from clinic or other selected samples are generally higher (12% to 33%). Epidemiologists, clinicians, therapists, and physiologists should work together to formulate standard definitions that can be applied to large population groups to obtain reliable and valid estimates of the prevalence and incidence of various types of female sexual dysfunction in the community. In this way, the true burden of these disorders can be established.
Little is known about risk factors for female sexual dysfunction or changes over the life span (natural history). Longitudinal data from representative samples are needed for this. A thorough epidemiologic examination of suspected risk factors for well-defined categories of sexual dysfunction can provide help determine in identifying etiologic factors, an important first step in planning treatment and prevention efforts.