Editing Menarche (section)

===Timing===
====Chronic illness====
Certain systemic or chronic illness can delay menarche, such as [[diabetes mellitus type 1]], [[cystic fibrosis]], [[asthma]], [[inflammation|inflammatory diseases]],<ref name=UmlawskaKrzyzanowska2009>{{cite journal | vauthors = Umławska W, Krzyzanowska M | title = [Puberty in certain chronic illness] | journal = Pediatric Endocrinology, Diabetes, and Metabolism | volume = 15 | issue = 3 | pages = 216–18 | date = 2009 | pmid = 20384185 | type = Review }}</ref> and untreated [[celiac disease]],<ref name=LefflerGreen2015>{{cite journal | vauthors = Leffler DA, Green PH, Fasano A | title = Extraintestinal manifestations of coeliac disease | journal = Nature Reviews. Gastroenterology & Hepatology | volume = 12 | issue = 10 | pages = 561–71 | date = October 2015 | pmid = 26260366 | doi = 10.1038/nrgastro.2015.131 | s2cid = 15561525 | type = Review }}</ref><ref name=TersigniCastellani>{{cite journal | vauthors = Tersigni C, Castellani R, de Waure C, Fattorossi A, De Spirito M, Gasbarrini A, Scambia G, Di Simone N | display-authors = 6 | title = Celiac disease and reproductive disorders: meta-analysis of epidemiologic associations and potential pathogenic mechanisms | journal = Human Reproduction Update | volume = 20 | issue = 4 | pages = 582–93 | date = 2014 | pmid = 24619876 | doi = 10.1093/humupd/dmu007 | type = Review | doi-access = free | hdl = 10807/56796 | hdl-access = free }}</ref> among others.<ref name=TraggiaiStanhope2003>{{cite journal | vauthors = Traggiai C, Stanhope R | title = Disorders of pubertal development | journal = Best Practice & Research. Clinical Obstetrics & Gynaecology | volume = 17 | issue = 1 | pages = 41–56 | date = February 2003 | pmid = 12758225 | doi = 10.1053/ybeog.2003.0360 | type = Review }}</ref>  Sometimes, [[clinical chemistry|lab tests]] do not return determinative results, so that underlying pathologies are not identified and the girl is diagnosed with [[constitutional growth delay]].<ref name=WeiCrowne2015>{{cite journal | vauthors = Wei C, Crowne EC | title = Recent advances in the understanding and management of delayed puberty | journal = Archives of Disease in Childhood | volume = 101 | issue = 5 | pages = 481–88 | date = May 2016 | pmid = 26353794 | doi = 10.1136/archdischild-2014-307963 | s2cid = 5372175 | type = Review }}</ref>

====Conditions and disease states====
Studies have been conducted to observe the association of the timing of menarche with various conditions and diseases. Some studies have shown that there may be an association between early or late-age menarche and [[cardiovascular disease]], although the mechanism of the association is not well understood.<ref>{{cite journal | vauthors = Luijken J, van der Schouw YT, Mensink D, Onland-Moret NC | title = Association between age at menarche and cardiovascular disease: A systematic review on risk and potential mechanisms | journal = Maturitas | volume = 104 | pages = 96–116 | date = October 2017 | pmid = 28923182 | doi = 10.1016/j.maturitas.2017.07.009 }}</ref> A systematic review has concluded that early onset of menarche is a risk factor for [[insulin resistance]]<ref>{{cite journal | vauthors = Zhang Z, Hu X, Yang C, Chen X | title = Early age at menarche is associated with insulin resistance: a systemic review and meta-analysis | journal = Postgraduate Medicine | volume = 131 | issue = 2 | pages = 144–50 | date = March 2019 | pmid = 30560708 | doi = 10.1080/00325481.2019.1559429 | s2cid = 56178701 }}</ref> and [[breast cancer]] risk.<ref>{{cite journal | vauthors = Kapil U, Bhadoria AS, Sareen N, Singh P, Dwivedi SN | title = Reproductive factors and risk of breast cancer: A Review | journal = Indian Journal of Cancer | volume = 51 | issue = 4 | pages = 571–76 | date = 2014 | pmid = 26842199 | doi = 10.4103/0019-509X.175345 | doi-access = free }}</ref>

There is conflicting evidence regarding the association between [[obesity]] and timing of menarche; a meta-analysis and systematic review has determined that more studies must be conducted to make any definitive conclusions about this association.<ref>{{cite journal | vauthors = Li W, Liu Q, Deng X, Chen Y, Liu S, Story M | title = Association between Obesity and Puberty Timing: A Systematic Review and Meta-Analysis | journal = International Journal of Environmental Research and Public Health | volume = 14 | issue = 10 | pages = 1266 | date = October 2017 | pmid = 29064384 | pmc = 5664767 | doi = 10.3390/ijerph14101266 | doi-access = free }}</ref>

====Effects of stress and social environment====
Some of the aspects of family structure and function reported to be independently associated with earlier menarche [antenatal and early childhood]
* Being non-white (in the [[United Kingdom|UK]])<ref name="D.H. Morris, M.E. Jones 2010">{{cite journal | vauthors = Morris DH, Jones ME, Schoemaker MJ, Ashworth A, Swerdlow AJ | title = Determinants of age at menarche in the UK: analyses from the Breakthrough Generations Study | journal = British Journal of Cancer | volume = 103 | issue = 11 | pages = 1760–64 | date = November 2010 | pmid = 21045834 | pmc = 2994234 | doi = 10.1038/sj.bjc.6605978 }}</ref>
* Having experienced pre-eclampsia in the womb<ref name="D.H. Morris, M.E. Jones 2010"/>
* Being a singleton, i.e. not a twin or triplet<ref name="D.H. Morris, M.E. Jones 2010"/>
* Low birthweight<ref name="D.H. Morris, M.E. Jones 2010"/>
* Not having been breast-fed<ref name="D.H. Morris, M.E. Jones 2010"/>
* Exposure to smoking<ref name="D.H. Morris, M.E. Jones 2010"/>
* High-conflict family relationships<ref>{{cite journal | vauthors = Belsky J, Steinberg L, Houts RM, Halpern-Felsher BL | title = The development of reproductive strategy in females: early maternal harshness --> earlier menarche --> increased sexual risk taking | journal = Developmental Psychology | volume = 46 | issue = 1 | pages = 120–28 | date = January 2010 | pmid = 20053011 | doi = 10.1037/a0015549 }}</ref>
* Lack of exercise in childhood<ref name="D.H. Morris, M.E. Jones 2010"/>

Other research has focused on the effect of childhood [[Stress (biology)|stress]] on timing of puberty, especially female. Stress is a vague term and studies have examined conditions ranging from family tensions or conflict to wartime refugee status with threat to physical survival. The more dire social conditions have been found to be associated with delay of maturation, an effect that is compounded by inadequate diet and nutrition. There is mixed evidence if milder degrees of stress can accelerate puberty in girls as would be predicted by [[life history theory]] and demonstrated in non-human mammals.<ref>{{cite journal | vauthors = Mishra GD, Cooper R, Tom SE, Kuh D | title = Early life circumstances and their impact on menarche and menopause | journal = Women's Health | volume = 5 | issue = 2 | pages = 175–190 | date = March 2009 | pmid = 19245355 | pmc = 3287288 | doi = 10.2217/17455057.5.2.175 }}</ref>

The understanding of these environmental effects is incomplete and the following cautions are relevant:
* Most of these "effects" are statistical associations revealed by [[epidemiology|epidemiologic]] surveys. Statistical associations are not necessarily causal, and secondary variables and alternative explanations can be possible instead. Effects of small size studies can never be confirmed or refuted for any individual child.
* Despite the small magnitude of effect, interpretations of the studies are politically controversial because this type of research is often be used for political advocacy. Accusations of bias based on political agenda sometimes accompany scientific criticism.
* [[Correlation does not imply causation]]. While correlation can be objectively measured, causation is statistically inferred. For example, some suggest that childhood stress is caused by precocious puberty recognized later, rather than being the cause of it.<ref>[[The Australian]], 3 April 2013. [http://www.theaustralian.com.au/news/health-science/early-onset-puberty-causes-emotional-issues-at-preschool-age/story-e6frg8y6-1226611493370 Early onset puberty causes emotional issues at preschool age] {{webarchive |url=https://web.archive.org/web/20130416032021/http://www.theaustralian.com.au/news/health-science/early-onset-puberty-causes-emotional-issues-at-preschool-age/story-e6frg8y6-1226611493370 |date=April 16, 2013 }}</ref>

====Changes in time of average age====
[[File:Acceleration1.jpg|thumb|upright=1.8|Secular trend in decrease in age of menarche in Western European and North American girls; Boaz (1999)<ref>Boaz, N.T. (1999). ''Essentials of biological anthropology.'' Prentice Hall, New Jersey, {{ISBN|0-13-080793-1}}.</ref>]]

There were few systematic studies of timing of menarche before the second half of the 20th century. Most older estimates of average onset of menarche were based on observation of a small, homogeneous, non-representative sample of the larger population, or based on recall by adult women, which is susceptible to error. Most sources agree that the average age of menarche in girls in modern societies has declined, though the reasons and the degree remain subjects of study. 

From the sixth to the 15th centuries in Europe, most women reached menarche at about 14, between the ages of 12 and 15.<ref>{{cite journal |author1=Amundsen Darrel |author2=Dreis Carol Jean | year = 1973 | title = The Age of Menarche in Medieval Europe | journal = Human Biology | volume = 45 | issue = 3| pages = 363–68 |pmid=4584336 }}</ref> The average age of menarche dropped from 14-15 years in the early 20th century to 12-13 years in the present, but girls in the 19th century had a later age of menarche (16 to 18 years) compared to girls in earlier centuries.<ref>{{cite web |title=Average age of Menarche in History |work=British Medical Journal |url=https://www.bmj.com/content/322/7294/1095.full}}</ref> A large North American survey reported a 2–3 month decline from the mid-1970s to the mid-1990s.<ref name=AndersonEtAl2003>{{cite journal |vauthors = Anderson SE, Dallal GE, Must A |title = Relative weight and race influence average age at menarche: results from two nationally representative surveys of US girls studied 25 years apart |journal = Pediatrics | volume = 111 |issue = 4 Pt 1 | pages = 844–50 | date = April 2003 | pmid = 12671122 | doi = 10.1542/peds.111.4.844 }}</ref> A 2011 study found that each 1&nbsp;kg/m<sup>2</sup> increase in childhood [[body-mass index]] (BMI) can be expected to result in a 6.5% higher absolute risk of early menarche (before age 12 years).<ref>{{cite journal | vauthors = Mumby HS, Elks CE, Li S, Sharp SJ, Khaw KT, Luben RN, Wareham NJ, Loos RJ, Ong KK | display-authors = 6 | title = Mendelian Randomisation Study of Childhood BMI and Early Menarche | journal = Journal of Obesity | volume = 2011 | page = 180729 | year = 2011 | pmid = 21773002 | pmc = 3136158 | doi = 10.1155/2011/180729 | doi-access = free }}</ref> This is called the '''secular trend'''.<ref name="Strickland2001">{{cite book|editor-first1=Bonnie B.|editor-last1=Strickland|title=The Gale Encyclopedia of Psychology|url=https://books.google.com/books?id=kSoZAQAAIAAJ&pg=PA528 |year=2001 |chapter=Puberty |chapter-url=<!-- not a Google Books -->|publisher=Gale Group|isbn=978-0-7876-4786-5|page=528 |edition=Second |quote=The sequence and age range of the developmental changes associated with puberty can vary widely. Although most children begin puberty between the ages of 10 and 12, it can start at any age from 8 to 16. The most obvious determining factor is gender; on average, puberty arrives earlier for girls than boys. Heredity also appears to play an important role. Compared to an overall age range of nine to 18 for menarche, the age difference for sisters averages only 13 months and for identical twins, less than three months. Body weight is a factor as well: puberty often begins earlier in heavier children of both sexes and later in thinner ones. The onset of menstruation, in particular, appears to be related to amounts of body fat. Girls with little body fat, especially athletes, often start menstruating at a later than-average age. Over the past 100 years, puberty has tended to begin increasingly early in both sexes (a phenomenon called the ''secular trend'').}}</ref><ref>{{cite book |first=Laurence |last=Steinberg|editor-first1=Bonnie B.|editor-last1=Strickland  |title=The Gale Encyclopedia of Psychology |year=2000 |chapter=Adolescence |chapter-url=|publisher=Gale Group|isbn=0-7876-4786-1 |page=11 |edition=Second |quote=The timing of physical maturation varies widely. In the United States today, menarche, the first menstrual period, typically occurs around age 12, although some youngsters start puberty when they are only eight or nine, others when they are well into their teens. The duration of puberty also varies greatly: eighteen months to six years in girls and two to five years in boys.}}</ref>

In 2002, fewer than 10% of U.S. girls started to menstruate before 11 years of age, and 90% of all U.S. girls were menstruating by 13.75 years of age, with a median age of 12.43 years. This age at menarche is not much different (0.3 years earlier) than that reported for U.S. girls in 1973. Age at menarche for non-Hispanic black girls was significantly earlier than that of white girls, whereas non-white Mexican American girls were only slightly earlier than white girls.<ref name=Chumlea>{{cite journal | vauthors = Chumlea WC, Schubert CM, Roche AF, Kulin HE, Lee PA, Himes JH, Sun SS |title = Age at menarche and racial comparisons in US girls | journal = Pediatrics | volume = 111 | issue = 1 | pages = 110–13 | date = January 2003 | pmid = 12509562 | doi = 10.1542/peds.111.1.110 }}</ref>