Fatigue is a common issue among teenage girls and can significantly affect their daily lives, including school attendance and social interactions. While iron deficiency and anaemia are often seen as the main causes of fatigue, recent research suggests that the situation is more complex than previously thought. A study involving 485 Swedish high school girls found that 38% had iron deficiency, and many experienced heavy menstrual periods (54%) or followed a diet with little or no meat (27%). Despite these factors, the study found that iron deficiency or anaemia was not linked to higher fatigue levels or worse quality of life. In fact, lower levels of ferritin (a protein that stores iron) and haemoglobin (a protein in red blood cells that carries oxygen) were associated with less fatigue, even after adjusting for other factors. Instead, the study found that heavy periods were strongly linked to increased fatigue and poorer quality of life, even when iron levels were taken into account. Other factors related to heavy periods—like menstrual pain, poor sleep, or missing school and social activities—may play a larger role in causing fatigue than iron deficiency itself. Similarly, skipping meals or using nicotine products like snus or cigarettes was also associated with higher fatigue and lower wellbeing. These findings are important because heavy periods, skipped meals, and nicotine use are factors that can be addressed if they are recognized as potential causes of fatigue. However, the study had limitations. It did not consider other possible influences on fatigue, such as socioeconomic status, physical activity, mental health, or sleep quality. Also, it could not determine whether these factors cause fatigue or are simply related to it. For example, a girl might skip breakfast because she is tired, or nicotine use could be a sign of other lifestyle factors that contribute to fatigue. Iron deficiency remains a significant health concern, as it is the leading cause of anaemia worldwide. Iron is crucial for transporting oxygen to the body’s organs, supporting muscle function, and maintaining brain health. Teenage girls are especially at risk due to increased iron needs during growth, combined with blood loss from menstruation and dietary choices that may lack sufficient iron. Researchers are now working to develop a simple five-question screening tool to help identify iron deficiency more effectively. They are also exploring which symptoms and treatment strategies are most helpful for this group.