Your Ethnicity Could Actually Impact the Length of Your Period, Study Says

One surprising factor could affect the length of your menstrual cycle: your ethnicity.

A new report from researchers at the Harvard T.H. Chan School of Public Health is shedding light on how menstrual cycles vary among people who menstruate. The research team analyzed data from 12,608 volunteer participants via a period tracking app. In total, they investigated more than 165,000 unique cycles.

Researchers also intentionally recruited participants based on whether they menstruate, not their gender identity. “This is important because most of our landmark studies on menstrual cycles are from the 1960s and they’re largely homogenous,” lead author Huichu Li, a doctoral student at the T.H. Chan School of Public Health, told NewScientist.

Consider this your periodic reminder that cisgender women aren’t the only people with periods! Transgender men, some intersex people, and nonbinary people who were assigned female at birth can also menstruate.

Their findings were fascinating: On average, menstrual cycles were 1.6 days longer among Asian people and .7 days longer among Hispanic people versus their white, non-Hispanic counterparts. (The team’s statistical analysis suggests this wasn’t a coincidence, either.) Asian and Hispanic people were also more likely to experience “cycle variability,” meaning their periods lasted for different amounts of time month over month.

Interestingly enough, researchers didn’t observe any significant differences in cycle length among other ethnic groups within the dataset, including Black, American Indian, Alaska Native, Middle Eastern, or North African people.

Researchers aren’t totally sure why these variations occur, but they have some theories. It’s likely due to a combination of factors, such as stress levels, cultural norms, and environmental exposures.

“Some possible factors may include systemic racial disparity, e.g. inequity in socioeconomic status, access to healthcare and exposure to the environment, such as endocrine-disrupting chemicals in personal care products,” Li added.

This report comes on the heels of some other interesting research into cycle trends among people who menstruate. A research brief from late September confirmed a link between the COVID-19 vaccine and “small, within the normal range of variation, and temporary” changes to the length of peoples’ periods. It’s an area of study worth further exploration considering roughly half the world’s population experiences menstrual periods.

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