Imagine having a hangover that never went away, or feeling exhausted even after the simplest errand. Chronic fatigue syndrome has been described as an "incapacitating tiredness" and afflicts more than half a million Americans. Still, little is known about what causes the disease–doctors usually diagnose it only when other conditions are ruled out. Now, scientists from the Royal Free and University College Medical School in London say there might be a link between childhood activity level and chronic fatigue syndrome as an adult.

What the researchers wanted to know: What childhood habits might cause adult chronic fatigue syndrome?

What they did: The researchers used data from a large, multisubject survey that is currently following more than 10,000 British people born at the beginning of April 1970. When the participants were 5, 10, 16, and 29 years old, the researchers checked in on them with a variety of surveys about their healthand physical and educational development. When the children were 10 years old, parents and teachers were interviewed about things including parental illnesses, parents' mental health, students' educational achievement, and the amount of physical activity children had in school. At 29, the participants were asked whether or not they had chronic fatigue syndrome.

What they found: The people who told the researchers they had chronic fatigue syndrome were more likely to be from a high socioeconomic background and not to have regularly played a sport when they were 10 years old. This result is at odds with an earlier study, which concluded that children who exercised a lot had a higher risk of developing chronic fatigue. Previous research has shown that children whose parents have had a long illness or a mental illness are more likely to develop chronic fatigue; this study found no link between to those parental issues. Overall, fewer than 1 percent of the study participants reported having chronic fatigue syndrome.

What it means to you: Chronic fatigue syndrome remains a mystery, but each study that chips away at the causes and mechanisms of the disease helps. This study, in contrast to others, supports the idea that having an active lifestyle, even as a child, helps to prevent later health problems–including chronic fatigue.

Caveats: Chronic fatigue syndrome is notoriously hard to diagnose, and many people go for years without knowing that they have it. This study asked people if they had chronic fatigue syndrome but not if they had been medically diagnosed with it. The study likely missed some people that do actually have it but aren't aware that they do, and may have picked up a few people who are often tired (either from stress or from another condition) but do not have chronic fatigue syndrome.

Find out more: Several organizations support chronic fatigue syndrome research and patients. One is the American Association for Chronic Fatigue Syndrome and another is The CFIDS Association of America. There is also a good description of the condition on the National Institutes of Health website.

If you want to learn more about the study that is giving researchers this trove of information, check it out at: www.cls.ioe.ac.uk

Read the article: Viner, R. and Hotopf, M. "Childhood Predictors of Self Reported Chronic Fatigue Syndrome/Myalgic Encephalomyelitis in Adults: National Birth Cohort Study." British Medical Journal. Oct. 23, 2004, Vol. 329, No. 7472.

Abstract online: http://bmj.bmjjournals.com