{"doi":"10.1101/2022.09.30.22280382","title":"Variation in menstrual cycle length by age, race/ethnicity, and body mass index in a large digital cohort of women in the US","abstract":"Abstract Background Menstrual characteristics are important signs of women’s health. We examined the variation of menstrual cycle length by age, race and ethnicity, and body weight using data collected from mobile menstrual tracking apps. Understanding how menstrual characteristics vary by these factors can provide important information for further study of environmental and social determinants of menstrual health. Methods We collected self-tracked menstrual cycle data from participants of the Apple Women’s Health Study. Demographic and lifestyle characteristics were self-reported from surveys. Linear mixed effect (LME) models were used to estimate the differences in cycle length associated with age, race/ethnicity, and body mass index (BMI), adjusted for possible confounders or predictors of cycle length. Cycle variability was estimated by the change of within-individual standard deviations of cycle length. Findings A total of 165,668 cycles from 12,608 participants from US were included. After adjusting for all covariates, mean menstrual cycle length was shorter with older age across all age groups until age 50 and then became longer for those age 50 and older. Menstrual cycles were on average 1·6 (95%CI: 1·2, 2·0) days longer for Asian and 0·7 (0·4, 1·0) days longer for Hispanic participants compared to White non-Hispanic participants. Participants with Class 3 obesity (BMI≥40 kg/m 2 ) had 1·5 (1·2, 1·8) days longer cycles compared to those with healthy BMI (18·5≤BMI<25 kg/m 2 ). Cycle variability was smaller among participants in older age groups but became considerably larger for those in the oldest age categories (45-49 and 50+). Asian and Hispanic participants and those who were obese had larger cycle variability. Interpretation This study demonstrated differences in menstrual characteristics by age, race and ethnicity, and obesity using data collected from mobile health apps. Future studies should explore the underlying determinants of the racial and ethnic differences in menstrual characteristics. Funding Apple Inc. Research in context Evidence before this study We searched PubMed for studies on menstrual cycles with age, body weight, and race/ethnicity using the term “((“Menstrual Cycle”[Mesh:NoExp] OR menstrual cycle*[tiab]) AND (“Time Factors”[Mesh] OR cycle length*[tiab] OR variability[tiab] OR variation*[tiab])) OR (“Menstruation”[Mesh] AND (“Time Factors”[Mesh] OR length[tiab] OR variability[tiab] OR variation*[tiab]) AND 1950[pdat]:1986[pdat]) AND (“Age Factors”[Mesh:NoExp] OR “Race Factors”[Mesh] OR “Racial Groups”[Mesh] OR “Ethnicity”[Mesh] OR “ethnology” [Subheading] OR “Body Mass Index”[Mesh] OR “Body Weight”[Mesh:NoExp] OR “Overweight”[Mesh] OR age[tiab] OR ages[tiab] OR race[tiab] OR races[tiab] OR racial[tiab] OR ethnic*[tiab] OR body mass[tiab] OR bmi[tiab] OR weight[tiab] OR overweight[tiab] OR obes*[tiab]) NOT (“Animals”[Mesh] NOT “Humans”[Mesh])” from 1950 to August 3, 2022. This search yielded 2,064 sources and we identified 30 research articles comparing menstrual cycle length and/or variability by age, race/ethnicity, and/or body weight in population. Another 14 research articles were added to the search results by knowledge of existing literature. Of the 44 articles identified, studies on changes of menstrual cycle length and variability with age reported consistent results, although the age range of the participants differed across these studies. In general, menstrual cycles were longer and less regular in the first few years following menarche, but over the subsequent decades cycles tend to become shorter and more regular with older age until age 40-45, after which they can become increasingly longer and irregular until menopause. Obesity was associated with menstrual irregularity. However, the association with menstrual cycle length was less consistently reported. Some studies found obesity was associated with longer menstrual cycles while other studies reported null associations. Compared ","journal":"medRxiv","year":2022,"id":298398,"datarank":0.0,"base_score":0.0,"endowment":0.0,"self_citation_contribution":0.0,"citation_network_contribution":0.0,"self_endowment_contribution":0.0,"citer_contribution":0.0,"corpus_percentile":null,"corpus_rank":null,"citation_count":6,"citer_count":0,"citers_with_citation_signal":0,"citers_with_endowment":0,"datacite_reuse_total":0,"is_dataset":false,"is_dataset_confidence":0.9448,"is_data_producer":false,"deposit_databanks":null,"is_oa":true,"file_count":0,"downloads":0,"has_version_chain":false,"published_date":"2022-01-01","fair_score":null,"fair_percentile":null,"algorithm_id":"datarank_citation_only_1hop_v6","ranking_scope":"data_only","authors":[{"id":875022,"name":"Elizabeth A. Gibson","orcid":"0000-0001-5119-5133","position":1,"is_corresponding":false},{"id":431657,"name":"Anne Marie Z. Jukic","orcid":"0000-0001-8635-9505","position":2,"is_corresponding":false},{"id":294195,"name":"Donna D. Baird","orcid":"0000-0002-5544-2653","position":3,"is_corresponding":false},{"id":433685,"name":"Allen J. Wilcox","orcid":"0000-0002-3376-1311","position":4,"is_corresponding":false},{"id":422882,"name":"Christine L. Curry","orcid":"0000-0003-4783-9623","position":5,"is_corresponding":false},{"id":681999,"name":"Tyler Fischer‐Colbrie","orcid":"0000-0001-5723-800X","position":6,"is_corresponding":false},{"id":305790,"name":"Jukka‐Pekka Onnela","orcid":"0000-0001-6613-8668","position":7,"is_corresponding":false},{"id":364473,"name":"Michelle A. Williams","orcid":"0000-0001-5807-5281","position":8,"is_corresponding":false},{"id":307047,"name":"Russ Hauser","orcid":"0000-0002-1899-3982","position":9,"is_corresponding":false},{"id":94039,"name":"Brent A. Coull","orcid":"0000-0002-1808-4156","position":10,"is_corresponding":false},{"id":987841,"name":"Shruthi Mahaligaiah","orcid":null,"position":11,"is_corresponding":false},{"id":681996,"name":"Huichu Li","orcid":"0000-0002-7425-2775","position":0,"is_corresponding":true}],"reference_count":58,"raw_metadata":null,"created_at":"2026-07-19T00:31:36.269611Z","pmid":null,"pmcid":null,"fwci":null,"citation_percentile":null,"influential_citations":0,"oa_status":null,"license":null,"views":0,"total_file_size_bytes":0,"version_count":0,"fair_f":null,"fair_a":null,"fair_i":null,"fair_r":null,"fair_zscore":null,"fair_rationale":null,"fair_model":null,"fair_agent_version":null,"fair_fulltext_source":null,"fair_has_llm":null,"fair_computed_at":null,"clinical_trials":[],"software_tools":[],"db_accessions":[],"linked_datasets":[],"topics":[]}