Menarche

Onset

• From the 19th century through the mid-20th century, average age at menarche declined steadily in the United States and Europe, possibly due to improved nutrition and a reduction in strenuous physical activity. In the United States, average age at menarche declined from older than 14 years in 1877 to 12.8 years in 1947. Read more »
• In the United States, the age at menarche (AAM) varies from 11.96 to 12.93 years. About 10% of girls reach the AAM at 11 years old or younger, while 90% of girls reach AAM at 13.75 years with a median age of 12.43 years. Read more »
• African American (12.2 years) and Hispanic (12.3) girls tend to have a significant earlier AAM. The AAM for Asian girls is 13.00 ± 1.26 years. Read more »

Determininants of AAM

• Age at menarche is determined in part by hereditary and non-hereditary factors. The contribution of genetic factors is about 57-82%. Non-hereditary factors like a childhood diet that is high in animal protein and low in vegetable protein may also be linked with earlier menarche. Menarche tends to be earlier in girls with more body fat and later in girls who exercise. Read more »
• Higher body mass index (BMI) in girls as young as 36 months of age is associated to early menarche. A strong association between large waist circumference and early AAM has more predictive value than body weight for possible adverse outcomes in adulthood. Read more »
• Consuming animal protein (cow milk and meat) and soy-containing products promote early AAM through excessive energy intake and subsequent overweight. On the other hand, vegetable protein, fiber and vitamin D protect against rapid AAM. Read more »
• Girls exposed to regular high intensive physical exercises in childhood and adolescence delay AAM. Physical activity and nutritional deficiency influences AAM and lead to, an average, 1-year delay in AAM. Read more »
• Adverse childhood experience, such as sexual abuse, alcohol addicted or nervous troubled parents are strongly associated with early AAM. Read more »

Breast cancer risk associated to AAM

• AAM is a well-established breast cancer risk factor. Early AAM ≤12 vs ≥ 14 is associated with increased risk of young-onset breast cancer and invasive breast cancer. Breast cancer risk increased by a factor of 1.050 for every year younger at menarche. Read more »
• The longer the interval between menarche and first pregnancy the greater is a woman’s breast cancer risk. Therefore, menarche-to-first pregnancy represents a window of time when breast tissue is particularly vulnerable to carcinogenic stimuli. Read more »
• In a 2011 review by Lynch et al, the average reduction in breast cancer risk associated with physical activity at different ages was 16% for adolescence, 8% for early adulthood, 15% for middle adulthood, and 17% for age 50 and older. Read more »

Menopause

• Most estimates of age at natural menopause are based on samples of Caucasian women in western societies, although one international study of 18,997 women from 11 countries found the median age at natural menopause to be 50 years (range, 49–52 years).
• African-American women experience menopause 6–12 months earlier than Caucasians, with a median age of 49.3 years for African Americans.
• For Mexican women, median ages at menopause have been reported to be 48.2 years.
• Japanese women reported a median age at menopause of 50.4 years. Malaysian women reported a similar median age at menopause of 50.7 years. Thai women reported a median age at menopause of 49.5 years. Filipino Malay women were reported to be an average age of 47–48 years at menopause.

Read more on these statistics »

• About 85% of men report that their partner had an orgasm at the most recent sexual event; this compares to the 64% of women who report having had an orgasm at their most recent sexual event. (National Survey of Sexual Health and Behavior, 2010.)
• Men are more likely to orgasm when sex includes vaginal intercourse; women are more likely to orgasm when they engage in a variety of sex acts and when oral sex or vaginal intercourse is included. (National Survey of Sexual Health and Behavior, 2010.)
• Among ages 18-59, older age for men is associated with lower likelihood of his own orgasm; for women it is associated with a higher likelihood of her own orgasm. Age is not associated with the partner's orgasm for either men or women. (National Survey of Sexual Health and Behavior, 2010).
• Women are much more likely to be nearly always or always orgasmic when alone than with a partner. However, among women currently in a partnered relationship, 62% say they are very satisfied with the frequency/consistency of orgasm. Read more »
• It is possible to experience both genital and non-genital orgasm, even for some individuals with spinal cord injuries. (Functional MRI of the brain during orgasm in women, 2005).

There is wide variability in what people consider included in "having sex." According to the study, considerations of "sex" also varied depending on whether or not a condom was used, female or male orgasm, and if the respondent was performing or receiving the stimulation. Read more »

• 45% of participants considered performing manual-genital stimulation to be "having sex"
• 71% considered performing oral sex to be "sex"
• 80.8% considered anal-genital intercourse to be "sex"

• In a survey of adolescent (10-17 y/o) internet users found 42% had been exposed to internet pornography in the past year, with 66% of those exposures reported as unwanted. Read more »
• In a national study, 14% of people reported having used a sexually explicit website ever. Additionally, 25% of men reported visiting a pornographic site in the previous 30 days; 4% of women reported visiting pornographic sites in the same timeframe. Read more »

15% of men are estimated to have had sex with a prostitute. Read more »

• Despite common conceptions of prostitution, only a minority of prostitutes work on the streets (10–30%). While street prostitution receives the majority of legal attention, far more prostitutes work as escorts, call girls, or in massage parlors and brothels. Read more »
• [KI] 69% of white males had at least one experience with a prostitute. (Sexual Behavior in the Human Male, 1948)

• Over 50% of respondents ages 18-24 indicated that their most recent sexual partner was a casual or dating partner. For all other age groups, the majority of study participants indicated that their most recent sexual partner was a relationship partner. (National Survey of Sexual Health and Behavior, 2010).
• Men whose most recent sexual encounter was with a relationship partner reported greater arousal, greater pleasure, fewer problems with erectile function, orgasm, and less pain during the event than men whose last sexual encounter was with a non-relationship partner. (National Survey of Sexual Health and Behavior, 2010).
• Men and women both were likely to report sexual satisfaction if they also reported frequent kissing and cuddling, sexual caressing by the partner, higher sexual functioning, and if they had sex more frequently. On the other hand, for men, having had more sex partners in their lifetime was a predictor of less sexual satisfaction. Read more »
• [KI] Frequent kissing or cuddling predicted happiness in the relationship for men, but not for women. Both men and women reported more happiness the longer they had been together. Read more »
• Sexual dissatisfaction is associated with increased risk of divorce and relationship dissolution. Read more »

Sexual assault & nonconsensual sexual contact

• In 2006, there were 272,350 sexual assaults in the United States. This is one sexual assault every 116 seconds or about one every two minutes. Read more »
• Less than 5% of rapes were reported to law enforcement officials. Read more »
• Rape rates are often drastically high in war-torn nations. In Rwanda in 1994, it is estimated that between 250,000 and 500,000 women and girls were raped in less than 100 days (Human Rights Watch, 1996).
• 11.7% of student respondents across 27 universities reported experiencing nonconsensual sexual contact by physical force, threats of physical force, or incapacitation since they enrolled at their university. Read more »
• The incidence of sexual assault and sexual misconduct due to physical force, threats of physical force, or incapacitation among female undergraduate student respondents was 23.1%, including 10.8% who experienced penetration. Read more »
• One-third (33.1%) of senior females and 39.1% of seniors identifying as transgender/genderqueer or non-conforming/questioning report being a victim of nonconsensual sexual contact at least once. Read more »

Child sexual abuse

• Child sexual abuse is believed to affect 10-25% of girls worldwide (World Health Organization, 2004).
• In studies conducted mostly in developed countries, 5–10% of men report being sexually abused as children (World Health Organization, 2004)
• An estimated 100 million to 400 million women worldwide have been subjected to Female Genital Mutilation (FGM). About three million girls are subjected to the procedure every year (World Health Organization, 2006).

Sexual Orientation

• [KI] Kinsey Heterosexual-Homosexual Rating Scale - also known as "the Kinsey scale".
• An estimated 3.5% of adults in the United States identify as lesbian, gay, or bisexual. Read more »
• .5-1% of the United States population is estimated to be asexual (no attraction to anyone) Read more »
• In an analysis of national survey results from 2006-2008, the percentage reporting their sexual identity as homosexual ranged from 2–4% of males, and about 1–2% of females. Read more »

Sexual attraction & activity:

Opposite sex

• 95.3% of women and 93.5% of men aged 18–44 report ever having any opposite-sex sexual contact. (National Health Statistics Reports, 2016)
• Median number of opposite-sex partners in lifetime among U.S. men and women aged 25-44 years of age is 6.6 for men and 4.3 for women. (National Center for Health Statistics, 2015)
• Percentage of men and women aged 15-44 years of age who have had 15 or more opposite-sex sexual partners in their lifetime is 21.8% for men, and 10.6% for women. (National Center for Health Statistics, 2015)

Same sex

• Almost three times as many women (17.4%) reported any same-sex contact in their lifetime compared with men (6.2%) aged 18–44. (National Health Statistics Reports, 2016), See also: Prevalence of Homosexuality
• About 4%–6% of males ever had same-sex contact. For females, the percentage who have ever had same-sex contact ranges from about 4% to 11–12%. Read more »
• 19 million Americans (8.2%) report that they have engaged in same sex sexual behavior and nearly 25.6 million Americans (11%) report some same sex sexual attraction. Read more »

Bisexual attraction & activity

• In an analysis of national survey results from 2006–2008, the percentage reporting their sexual identity as bisexual is between 1–3% of males, and 2–5% of females. Read more »
• [KI] A 2011 study found that bisexual men exhibited a distinctive arousal pattern separate from heterosexual or homosexual men. Read more »

Transgender

• An estimated 0.3% of adults are transgender. Read more »
• A review of 8 transgender studies found rates for male-to-female between 1 in 11,900 to 1 in 45,000 and female-to-male between 1 in 30,400 to 1 in 200,000. (World Professional Association for Transgender Health, 2011)
• Among male-to-female transgender people (MtF), 27% are attracted to men, 35% are attracted to women, and 38% are attracted to men and women. Read more »
• Among female-to-male transgender people (FtM), 10% are attracted to men, 55% are attracted to women, and 35% are attracted to men and women. Read more »
• 12-27% of children continue to experience gender dysphoria as adults. (World Professional Association for Transgender Health, 2011)