Scientists may be able to predict who gets tired, and when, according to a new study from Yale that examined over 500 cancer patients.

The researchers sought to identify risk factors among cancer patients in the hopes of better understanding, preventing and alleviating fatigue. In the process, they discovered that morning and evening fatigue are distinct phenomena. The study, which is the first to demonstrate a difference between the two, will be published in the multidisciplinary Journal of Pain and Symptom Management.

“We looked at how the severity of fatigue is different based on [different] potential predictors,” said study lead author Fay Wright, who conducted the research for her dissertation at the College of Nursing at New York University.

Researchers were able to identify several risk factors for both morning and evening fatigue. For example, body mass index, anxiety and exercise habits displayed in reaction to stressful events and exercise habits were associated with morning — but not evening — fatigue. Those who had lower BMIs, displayed less anxiety or exercised more were less likely to be tired in the morning. Other factors, like sleep disturbance and depressive symptoms, contributed to both types of fatigue.

The team enrolled 586 patients, all of whom were over 18 years of age, had undergone at least one round of chemotherapy and had at least two more cycles of chemotherapy planned. They examined patients’ fatigue with two surveys — one which the patients took within 30 minutes of waking up and the other just before going to bed — using the highly reliable Lee Fatigue Scale to track fatigue severity in patients.

Additionally, they gathered demographic and clinical data from patients, looking at traits ranging from the mundane, such as BMI, to the complex, like family situation and childcare responsibilities, Wright said. The researchers then used a statistical method, which looked at fatigue over the course of the day and differences in specific predictors or characteristics that are directly associated with fatigue severity scores.

Wright noted that the study is particularly exciting because it is part of a larger, multi-site study, which means the data are more reliable. She said she thinks the findings are very close to being implemented on a clinical level.

According to Lingeng Lu, a researcher at the Yale Cancer Center, there is no doubt that the study could improve quality of life for cancer patients. In an email, Lu stressed the effects of fatigue on patients’ lives, calling it, “one of the most frequent side effects of cancer and its treatment.”

“Fatigue has been recognized as the number one symptom experienced universally by cancer patients,” said Ruth McCorkle, professor of epidemiology at the Yale School of Nursing.

The study, he said, could be influential in helping clinicians identify patients at high risk of fatigue and help individual patients take action to reduce the severity of the symptom. McCorkle said that being able to differentiate between contributing factors was exciting and could help give fatigued patients a sense of control over their situation.

Wright gave an example of the more personalized approach that could come from these findings. A clinician treating an overweight patient experiencing morning fatigue could recommend that the patient begin a regular exercise routine. Helping such a patient find a way to incorporate as much physical activity as comfortable into his or her daily life would address two of the study’s risk factors: decreasing BMI and increasing the amount of exercise in that patient’s life.

The study could contribute to the medical community’s wider movement towards personalized medicine, according to both Wright and Lu. Because Wright and her team sequenced participants’ DNA markers related to inflammation and fatigue, they will be able to conduct preliminary research into different genetic factors that affect patients’ differing responses to treatment.

The authors are considering publishing a separate paper looking at the researchers’ findings through a clinical lens, explaining how physicians, nurses and nurse practitioners can use the information to more effectively treat their fatigued patients.

The study was funded by the National Cancer Institute and the American Cancer Society.