A recently published study in the American Journal of Psychiatry took a look at the relationship between fatigue and depression in teenagers. Though fatigue is often thought to be a symptom of depression, the study showed that may not always be the case.
However, one of the authors of the study, Dr. Kathleen Merikangas, notes that fatigue — especially prolonged fatigue — can be a sign of other unhealthy behavior. We spoke to Merikangas, chief of the genetic epidemiology branch at the National Institute of Mental Health. Here is an edited version of our interview:
Q: What causes fatigue?
A: Fatigue can be multifactorial. Fatigue can be caused by acute illness such as a viral illness. People with cancer can get fatigued. The most common reason in adolescents is they don't get enough sleep.
Q: In the group you studied, what was the average amount of sleep?
A; We didn't present that in this paper. We're looking at that more carefully now. We're very interested in school start times and kids' activities to get a sense of sleep patterns.
Data from other sources shows that adolescents in America get an average of 1½ hours less of sleep (than is recommended in) guidelines from the National Sleep Foundation. For (each year of) high school it goes down at least half an hour (a night) on average. Americans in general do not get the recommended amount of sleep, and that goes across the age span.
Q: Are our children more fatigued than in the past? If so, why?
A: That we don't know. But there's an impression that children now are getting less sleep than they used to because of school activities. A lot of the school activities require the children to be at school earlier.
Q: Besides being tired, how did fatigue affect children in your study?
A: We were interested in kids who reported fatigue that was prolonged. We considered fatigue if they reported being tired for three months or more. (Study subjects reported) extreme tiredness or weakness. One of the criteria is that they become tired even after minor physical effort with muscular aches and pains, headaches and inability to relax. Any of us who miss sleep will, of course, feel tired the next day but oftentimes (fatigue also leads to) irritability, dizziness and so forth.
A lot of researchers and pediatricians believe that fatigue is a manifestation of depression or anxiety. We were interested in seeing what was the nature of the relationship.
Q: What were your findings as it relates to fatigue and depression?
A: We found a substantial number of youths who had both. But we also found an equal number of people who had fatigue only. Fatigue alone is not always a manifestation of some other psychological or emotional problem. Therefore, fatigue is not always associated with depression or anxiety.
Q: So which comes first — fatigue or depression?
A: Even though there are a substantial number of youths who have fatigue alone, there is a strong association between fatigue with depression and anxiety disorders. Among those adolescents who have both fatigue and depression, follow-up studies show that there is no specific pattern of onset of the two conditions. The onset of depression can occur after that of fatigue or fatigue can occur after the onset of depression.
Q: Why did you focus on young children?
A: We wanted to extend our national study of adults, and we have studied people over 18. (But there is) no data for children on a national level.
Q: What are the trends?
A: What we found in these studies is that these mental disorders — particularly anxiety — are very common in adolescents. We found that all of these (mental) disorders, when you look at the aggregate, are more common than the physical such as asthma, etc. We were able to share that mental disorders are fairly prevalent in adolescents. Most of (these mental disorders) begin to emerge in adolescence, and there are a number of children who don't get treatment.
Q: What's the solution?
A: Fatigue can be a very important symptom of some other illness because it impairs (youths') ability to perform in school and their relationships. Kids who are fatigued may smoke more. Other studies have found that there is more obesity in children who have fatigue. (It) can lead to a number of poor health behaviors that can have a lifelong impact. Obesity was particularly pronounced in kids with fatigue alone, and they also had a lot of physical pains.