Recently published findings from Lund University in Sweden challenge a common assumption about the causes of fatigue in teenage girls. The researchers found no link between iron deficiency and fatigue, even though iron deficiency was very common in the group. By contrast, heavy periods, skipping meals and daily nicotine use were linked to higher levels of self-reported tiredness in the group.
We had expected iron deficiency to be a major cause of fatigue in this group, but we did not find this to be the case," says Moa Wolff, a researcher and associate professor at Lund University who led the study. She is also a general practitioner within Region Skåne.
The study, published in Acta Psychologica, involved 485 girls aged 15-19 from upper secondary schools in Lund and Malmö. The participants answered questions on topics including fatigue, quality of life, menstruation, eating habits and nicotine use - and provided blood samples for analysis of ferritin and haemoglobin levels. Just over half of the participants met the criteria for heavy menstruation.
Iron deficiency was common: almost four in ten participants had ferritin levels below the WHO threshold (15 µg/L). However, when the researchers compared girls with and without iron deficiency, they found no clear difference in self-reported tiredness.
"Our findings do not suggest that iron deficiency is unimportant. Iron deficiency is very common in this group and may affect health in other ways; it may therefore require treatment. However, in this study, iron deficiency could not explain why some girls are more tired than others," says Anna Stubbendorff, PhD, a nutrition epidemiologist and researcher at Lund University who helped carry out the study.
Heavy periods and iron deficiency often occurred at the same time, but it was the heavy periods, not iron status, that were linked to fatigue. The difference between those who had heavy periods and those who did not was around 4-5 points on the 100-point fatigue scale.
"When a teenage girl presents with fatigue, doctors often ask about periods in order to identify risk factors for iron deficiency and anaemia. Our findings show that there is reason to pay attention to heavy periods as well, even when iron deficiency does not appear to explain the fatigue," says Moa Wolff.
So how do you know if you have a heavy period? Previously, the focus was on blood loss measured in millilitres, whereas today greater consideration is given to how the bleeding affects everyday life and quality of life.
"If your period is so heavy that it becomes a recurring problem in your everyday life, it's something you should seek help for - and treatment is available," says Moa Wolff.
Tiredness was also linked to lifestyle habits. Girls who used snus or smoked daily (38 used nicotine products daily, 8 smoked daily) reported feeling more tired, as did those who skipped breakfast or school lunch at least once a week (225 did not eat breakfast every day, and 97 did not eat school lunch every day).
"The connections are likely to run in several directions. Someone who is tired may skip breakfast more often, whilst irregular meals can affect energy levels and well-being. A cross-sectional study cannot determine cause and effect. Above all, the study's findings show that there is no single, simple explanation for fatigue in teenage girls," says Anna Stubbendorff.
The study also looked at dietary habits. Eating a vegetarian diet or otherwise limiting meat consumption was not linked to increased fatigue, even though the researchers had previously shown that iron deficiency was more common in these very groups.
"This illustrates rather well what we see in the study: factors that affect iron levels are not necessarily the same as those that determine how tired you feel," says Anna Stubbendorff.
At the same time, the researchers emphasise that the study did not examine several other factors that may influence fatigue, such as sleep, mental health, physical activity and socio-economic circumstances.
