Wikipedia states, without a particularly satisfying source, that:
Some sources say that achieving orgasm helps the uterus contract and expel the lining.
It does quote some other opinions there, though quick Googling yields people who buy this theory. What data can we find on the matter? Is this true? Does orgasm really trigger menstruation? If so how close temporally are the two events? How do they know that menstruation wouldn't have started when it did anyway?
That is just a misunderstanding. And one that does not make any sense in terms of human reproductive functions. If orgasm would trigger menstruations way out of the normal cycle than successful implantation of the fertilised egg would very seldom occur and no population would exist to propagate this idea.
How is a menstrual cycle defined, here that, is how long is a cycle:
The average menstrual cycle lasts 28 days. The variability of menstrual cycle lengths is highest for women under 25 years of age and is lowest, that is, most regular, for ages 25 to 39.[21] Subsequently, the variability increases slightly for women aged 40 to 44. […] Each cycle can be divided into three phases based on events in the ovary (ovarian cycle) or in the uterus (uterine cycle). The ovarian cycle consists of the follicular phase, ovulation, and luteal phase whereas the uterine cycle is divided into menstruation, proliferative phase, and secretory phase.
What does the claim say about that:
Ways to Shorten a Menstrual Cycle
For many women, the menstrual cycle can last anywhere from a week to two weeks each month.
That is they mix up the definitions.
Intercourse or Masturbation
Achieving orgasm through sexual intercourse or masturbation may also shorten the length of menstruation. According to Everyday Health, this is due to the additional contractions that the uterus experiences during orgasm, which may help to shed menstrual blood faster. An added bonus is that cramp relief may also occur thanks to the endorphins released during the sexual act.
Orgasm can influence menstruation. It may help in shortening the time of bleeding/menstruation – it does not say it will shorten the length of what is properly defined as a menstrual cycle.
The body text in the claim in question is correct in its own paragraph. The rest of the article and the headline confuse the terms and do not match with this paragraph.
Some references. And a small thought on how this might have caught on on the web: Orgasms, or better intercourse, might sometimes trigger some small irregular blood flow like in spotting or from small injuries. That may be misreported on the web as "menstruating". Since this post has a title with "trigger" different from the actual 'claim': If "the time" is right then an orgasm might make bleeding appear a little sooner than otherwise expected, but only in terms of hours not days. This post hoc ergo propter hoc reasoning is another factor for the internet bubble resulting from this.
The menstrual cycle can be influenced by many factors:
Common reasons for cycle irregularities: - Life stages and pregnancy
After menarche (the years after menstruation begins), Perimenopause (as cycles come to an end), Pregnancy, The postpartum period (after a pregnancy), Miscarriage (known or unknown), Abortion - Contraceptives
Changing or stopping hormonal birth control, IUDs, Emergency contraception, - Sleep/Wake Cycles
Shift work or working night shifts, Sleep disorders, Jet lag/long distance travel - Physical/Emotional Changes
Big emotional changes, such as grief, Quick weight loss, Not getting enough calories, Intensive exercise, Certain medications - a long list of medical conditions
Scientific investigation reveals the following:
Factors Affecting Menstrual Cycle Characteristics: … smoking, physical activity, ethnicity, and alcohol consumption … The length and regularity of menstrual cycles reflect changes in ovarian steroid production … However, self-reported bleeding patterns cannot distinguish ovulatory and anovulatory cycles or timing of ovulation in ovulatory cycles. … Previous epidemiologic studies have examined the effects of psychological stress in the workplace, caffeine consumption, smoking, and occupation on menstrual function by using daily urinary hormone metabolites. … These results suggest that nonmodifiable host factors, such as ethnicity, and potentially modifiable risk factors, such as smoking, physical activity, and alcohol consumption, may affect menstrual cycle outcomes. Therefore, both genetic and environmental factors may influence these characteristics, which in turn are related to long-term disease risk.
S D Silberstein & G R Merriam: "Physiology of the Menstrual Cycle (2000)": The menstrual cycle is the result of a carefully orchestrated sequence of interactions among the hypothalamus, pituitary, ovary, and endometrium, with the sex hormones acting as modulators and effectors at each level. Oestrogen and progestins have potent effects on central serotonergic and opioid neurons, modulating both neuronal activity and receptor density. There are a lot of possible influences on the length of the menstrual cycle. Physical, emotional, you name it. Orgasm hits some of these checkmarks and is also related to many hormonal changes before, during and after. But most relevant to the claim is:
Kenneth Mah & Yitzchak M. Binik: "The Nature of Human Orgasm: A Critical Review of Major Trends" (2001): While some researchers believed that female orgasm facilitates sperm retention (e.g., Baker & Bellis, 1993; Fox & Fox, 1967; Fox, Wolff, & Baker, 1970; Singh, Meyer, Zamborano, & Hurlbert, 1998), the physiological changes seen are generally not ascribed functions other than as a sexual response. Masters and Johnson (1966) noted that the anterior third of the vagina becomes vasocongested during arousal to form the orgasmic platform. Female orgasm consists of contractions of the orgasmic platform and the uterus, though the latter has rarely been measured (cf. Fox et al., 1970).
Naomi M. Morris & J. Richard Udry & Louis E. Underwood: "A Study OF The Relationship Between Coitus and The Luteinizing Hormone Surge" (1977) Our findings suggest that there is no causal relationship in humans between marital coitus and ovulation.
That means that of the many factors implicated in variations of the menstrual cycle, orgasm is not causative. For that to be theoretically possible much longer lasting hormonal changes would be required.
