Table 1. Nutrition/Energy Factors continued...
Psychologic and symptom distress have also been found to be significant predictors of fatigue.[46,47] In a study of 101 women about to undergo surgery for breast cancer, younger age, presurgery distress, and expectations about fatigue significantly predicted fatigue levels 1 week after surgery. In the regression model, age, distress and expectancy each uniquely contributed to fatigue, with distress and expectancy accounting for 25% of the variance.[Level of evidence: III] In a longitudinal study with women who had gynecologic cancer, symptom and psychologic distress significantly predicted fatigue before, during, and after treatment with chemotherapy, explaining up to 80% of the variance in fatigue scores after chemotherapy treatment.
Impairment in cognitive functioning, including decreased attention span and impaired perception and thinking, is commonly associated with fatigue.[48,49] Although fatigue and cognitive impairments are linked, the mechanism underlying this association is unclear. Mental demands inherent in the diagnosis and treatment of cancer have been well documented, but little is known about the concomitant problem of attention fatigue in people with cancer. Attention problems are common during and after cancer treatment. Some of the reported attention problems may be caused by the fatigue of directed attention.[50,51] Attention fatigue may be relieved by activities that promote rest and recovery of directed attention. Although sleep is necessary for relieving attention fatigue and restoring attention, it is insufficient when attention demands are high. Empirical literature suggests that the natural environment contains the properties for restoring directed attention and relieving attention fatigue.
Sleep Disorders and Inactivity
Disrupted sleep, poor sleep hygiene, decreased nighttime sleep or excessive daytime sleep, and inactivity may be causative or contributing factors in CRF. Patients with less daytime activity and more nighttime awakenings were noted to consistently report higher levels of CRF. Those with lower peak-activity scores, as measured by wristwatch activity monitors, experienced higher levels of fatigue.
Sleep disorders clearly contribute to fatigue  and may differentially affect fatigue ratings, depending on the time of the rating. A study evaluating fatigue in women undergoing radiation therapy for breast cancer found that sleep had a greater influence on morning fatigue values than on evening fatigue scores. In a similar study of men undergoing radiation therapy for prostate cancer, sleep contributed to both morning and evening fatigue levels. However, fatigue and sleep can also be distinct problems. One study that resulted in significant improvement in sleep with the use of cognitive behavioral therapy did not significantly affect fatigue.