標準BMIを保つことは月経周期の安定につながる～月経管理アプリ『ルナルナ』大規模データで明らかに～

2026-07-08 国立成育医療研究センター

【図1：標準BMI 付近で月経周期は最も安定（模式図）】

＜関連情報＞

• https://www.ncchd.go.jp/press/2026/0708.html
• https://www.nature.com/articles/s44294-025-00065-z

スマートフォンアプリユーザーを対象とした前向きコホート研究における体格指数と月経不順の関係 Body mass index and menstrual irregularity in a prospective cohort study of smartphone application users

Shiori Itoi,Makiko Sampei,Takayuki Tatsumi,Yutaka Osuga,Kaori Koga,Satoshi Narumi & Naho Morisaki
npj Women’s Health  Published:27 February 2025
DOI:https://doi.org/10.1038/s44294-025-00065-z

Abstract

Those in the extremities of the body mass index (BMI) spectrum are associated with an increased risk of menstrual irregularities, though previous large-scale studies show inconsistent findings. This study evaluated the relationship between BMI and menstrual cycle irregularity using data from 8745 individuals and 191,426 menstrual cycles collected from a smartphone application. Cubic spline models demonstrated a J-shaped curve for the average cycle length(CL), variability of CL, and absent/infrequent menstrual bleeding, indicating that both higher and lower BMI than normal were associated with longer, irregular cycles. An inverted J-shaped curve was found for the proportion of biphasic cycles, suggesting a higher risk of anovulatory cycles for both higher and lower BMI than normal. These findings highlight the benefits of maintaining a normal BMI for reproductive health.