Study finds teen girls' fatigue tied to heavy periods and skipped meals, not iron deficiency

A study of teenage girls in Sweden has found that persistent fatigue is linked to heavy menstrual bleeding, skipped meals and daily nicotine use — but not to iron deficiency, despite iron deficiency being common in the group and widely assumed to be a leading cause of tiredness in adolescent girls. The research, conducted by scientists at Lund University and published in the journal Acta Psychologica, surveyed 485 girls aged 15 to 19 at upper secondary schools in Lund and Malmö, pairing questionnaires on fatigue, diet, menstruation and nicotine use with blood tests for ferritin and hemoglobin.

The findings complicate a common clinical assumption: that low iron is the default explanation for why teenage girls report feeling drained. Instead, the researchers found that everyday, modifiable habits carried a stronger statistical relationship to self-reported exhaustion than blood iron markers did.

The numbers

Nearly 40 percent of the girls in the study had ferritin levels below the World Health Organization's threshold for iron deficiency, and roughly 8 percent met the criteria for anemia — rates in line with prior estimates of iron deficiency among adolescent girls, a population the Office on Women's Health has long flagged as being at elevated risk because of menstruation and growth demands. Yet iron status showed no meaningful correlation with how tired the girls said they felt.

What did correlate: girls who reported heavy menstrual bleeding scored four to five points higher on the study's 100-point fatigue scale than those who did not. Girls who skipped breakfast, lunch or both on one or more days a week reported significantly greater tiredness and lower overall well-being, as did the roughly 46 participants who said they used nicotine daily, whether through smoking or oral nicotine pouches such as snus. In an adjusted statistical model, higher ferritin and hemoglobin were even associated with slightly more fatigue rather than less — a counterintuitive result the authors attribute to reverse causation, since girls already struggling with tiredness may have started iron supplements before enrolling in the study, muddying the underlying relationship.

How researchers got here

Fatigue is one of the most common complaints adolescent girls bring to primary care, and iron-deficiency anemia has for decades been the default diagnostic suspect, given how closely the two symptoms overlap and how frequently menstruating teenagers run low on iron. Standard practice in many clinics is to check ferritin and, if it is low, treat with supplements and expect fatigue to improve. The Lund team set out to test that assumption directly by measuring fatigue and iron status side by side in a general adolescent population, rather than in a clinical sample already selected for anemia.

The researchers used a cross-sectional design, meaning all measurements were taken at a single point in time, which the authors themselves note as a limitation: it can identify associations but not prove that skipped meals or nicotine use directly cause fatigue rather than simply accompanying it. The study also did not measure sleep duration, mental health, physical activity or socioeconomic status, all of which are independently linked to tiredness in teenagers and could be confounding the results.

Who is affected

The study's authors say the practical stakes are significant for the roughly half of American and European teenage girls who menstruate through adolescence while also juggling school schedules that often crowd out regular meals. Heavy menstrual bleeding alone affects about one in five women and girls in any given year, according to federal guidance from the Office on Women's Health, and it frequently goes unmentioned in routine pediatric visits unless a patient is specifically asked about it. Daily nicotine use, meanwhile, remains common among American teenagers: the Centers for Disease Control and Prevention has reported that e-cigarettes remain the most commonly used tobacco product among U.S. youth, with nicotine pouches and other oral products increasingly popular alongside vaping.

Clinicians who treat teenagers say the findings, if replicated, argue for broadening the standard fatigue workup beyond a ferritin blood draw to include direct questions about menstrual flow, meal patterns and nicotine use — questions that can be asked without laboratory equipment and that point toward interventions a primary-care doctor or school nurse can act on immediately.

Reaction

Moa Wolff, an associate professor at Lund University and one of the study's lead researchers, said the team had expected the opposite result. "We had expected iron deficiency to be a major cause of fatigue but did not find this to be the case," Wolff said in comments released alongside the study.

"There is no single, simple explanation for fatigue in teenage girls," said Anna Stubbendorff, a nutrition epidemiologist at Lund University and a co-author of the study.

Stubbendorff added that the factors driving low iron levels appear to be distinct from the factors driving how tired a person actually feels, which is why treating a low ferritin reading in isolation may not resolve a patient's fatigue. The authors were careful to note that iron deficiency still matters for other reasons — untreated, it can affect concentration, immune function and long-term health — even if it turned out not to explain fatigue scores in this particular sample.

What happens next

The research team is calling for longitudinal studies that track the same girls over time and incorporate sleep, mental health and activity data, which would allow researchers to test whether heavy periods, skipped meals and nicotine use actually cause fatigue or simply travel alongside it. In the meantime, the authors say pediatricians and school health staff can act on the associational findings by screening for menstrual bleeding patterns, eating habits and nicotine use as part of a routine fatigue evaluation, rather than relying on an iron panel alone. The study was funded by Sweden's Southern Health Care Region, the Lions Research Fund Skåne and regional clinical research funding, and the full results were published in Acta Psychologica in August 2026.