Poor Sleep Hygiene is Associated with Decreased Discrimination and Inattention on Continuous Performance Task in Doctor of Physical Therapy Students: A Cross-sectional Study

Abstract

Introduction:

Reduced sleep quality impairs learning, memory formation, attention, and executive function ability. Poor sleep quality or sleep hygiene has been shown to impair academic performance of undergraduate and medical students. The purpose of this study was to examine the association between sleep quality, sleep hygiene, and cognitive performance in Doctor of Physical Therapy (DPT) students.

Methods:

Fifty DPT students at the University of Kansas Medical Center completed the Pittsburgh Sleep Quality Index (PSQI) and the Sleep Hygiene Index (SHI). Cognitive performance was assessed using the Continuous Performance Test (CPT) which is a test of sustained attention and the Trail-Making Task (TMT) to assess executive functioning. An actigraph was worn for one week to objectively characterize sleep outcomes. Spearman’s correlations were performed to assess the association between self-report sleep quality, sleep hygiene, and outcomes on the cognitive tasks. Post-hoc Mann-Whitney and Kruskal-Wallis tests were conducted to examine group differences between sleep outcomes and cognitive performance for demographic variable categories.

Results:

Twenty-three students (46%) reported poor sleep quality, and 27 participants (54%) had objectively-reported poor sleep quality. There was a significant positive correlation between SHI and Detectability (r_s= 0.297, p= 0.036) and Omissions (r_s=.343, p=0.015). There were group differences between sex and number of pets on the CPT outcomes, and there was a significant group difference between the number of drinks/week categories on the SHI.

Discussion and Conclusions:

About half of the participants were identified as having poor sleep quality. Poorer sleep hygiene was associated with poorer discrimination and inattention, which could potentially impact the students’ academic and clinical performance as well as their health and wellbeing. Also, certain demographic variables may modulate the results.

Introduction/Review of Literature

Graduate education is often associated with increased stress and academic expectations for students, which can contribute to changes in sleep hygiene.^1,2 Sleep hygiene refers to the behaviors (i.e. maintaining a regular sleep schedule, avoiding naps, avoiding caffeine and screens before bed) and environmental conditions (i.e. maintaining a dark, quiet, comfortable bedroom) that promote sleep quality. As would be expected, poor sleep hygiene and poor sleep quality have been found to be associated.¹ Research shows that less knowledge of appropriate sleep hygiene is associated with poorer sleep quality in medical students.^1,3

Sleep is of particular interest in healthcare education because these students have large volumes of information to learn, need to be able to pay attention for extended periods of time, problem-solve, and maintain responsibility for the care of patients. A decrease in sleep quality may impact the ability to learn material, make sound decisions, and deliver quality patient-care.^4,5

Students in medical education and nursing programs have been found to have a high prevalence of sleep disorders and poor sleep quality.^1,3,6,7 One study that relied on self-reported sleep quality in nursing students found that out of 364 students, 26.7% reported experiencing insomnia, and the prevalence was higher in older students.⁸ In another study that focused on sleep disorders in medical students in Iran, 38.2% reported moderate clinical insomnia and 7.1% had severe insomnia.⁹ In addition, 76% of medical students in Saudi Arabia reported poor sleep quality.¹⁰ One study including five academic medical centers in the U.S. found that 84% of residents reported excessive daytime sleepiness for which a clinical intervention would be indicated.¹¹ This high prevalence of sleep disorders and poor sleep quality may have an impact on the students’ academic performance, learning, memory, cognitive functioning, and their overall health.

Sleep has been shown to be critical for learning and memory consolidation.¹² Memory consolidation occurs “offline” during sleep due to the permissive environment that allows each memory to be integrated into the existing network of long-term memories.¹³ Poor sleep hygiene or sleep quality has been associated with poorer academic performance in undergraduate² and medical students.³ In medical students, poorer sleep quality was significantly correlated with lower GPA.¹⁰ One study found that poor sleep quality and high stress were associated with lower academic performance in medical students.¹⁴ These studies suggest that poor sleep quality, along with stress, possibility contribute to poorer student academic performance.

In addition to impairing learning, poor sleep quality and sleep disturbances have been shown to interfere with optimal cognitive functioning. A recent meta-analysis of 24 studies found that attention, information processing, memory, and complex decision-making are all components of cognitive function that are negatively impacted by insufficient sleep.¹⁵ One study suggested that insufficient sleep can contribute to a notable decline in attention and working memory because both are processed by the frontal lobe, which is particularly vulnerable to the effects of excessive wakefulness and sleep deprivation.¹⁶ Poor executive functioning, including impaired problem-solving abilities, has been shown to contribute to medical errors.^17,18

Entry-level physical therapy education in the United States typically consists of 2–3 years of graduate education and culminates with a doctoral degree. Considering that sleep insufficiency and poor sleep quality have been reported in other graduate-level healthcare education fields (namely medical education),^6,19,20 it is likely that sleep issues would be common in entry-level Doctor of Physical Therapy (DPT) students. However, the prevalence of poor sleep quality has never been examined in this population. Also, the relationship between sleep quality, sleep hygiene, and cognitive performance in physical therapy students has yet to be examined. Therefore, the purpose of this study is to assess the prevalence of poor sleep quality in DPT students and to explore the association between sleep quality, sleep hygiene, and cognitive performance in DPT students.

Subjects

Fifty individuals enrolled in the entry-level DPT program at the University of Kansas Medical Center participated in this study. The study was approved by and conducted in accordance with the (removed for blinding) institutional review board. Individuals were invited to participate if they had completed at least one semester of course work in the DPT program. Individuals were excluded if they reported having been diagnosed with a sleep disorder by a physician or if they reported any medical condition prohibiting them from wearing an actigraph for one week.

Methods

To assess self-report sleep quality and sleep hygiene practices, participants completed the Pittsburgh Sleep Quality Index (PSQI)²¹ and the Sleep Hygiene Index (SHI).²² The PSQI is a validated and reliable measure of self-report sleep quality. A global score of 5 or more reflects poor sleep quality. The SHI consists of a 13-item questionnaire answered on a 5-point Likert scale indicating likelihood of performing the behaviour with 0 being “never” and 4 being “always”. A higher score indicates poorer sleep hygiene. Participants were instructed to wear an actigraph (wGT3X-BT®, ActiGraph corp. Pensacola, FL) on their non-dominant wrist for seven consecutive days to assess sleep characteristics. The outcomes from the actigraph used to assess sleep characteristics were: total sleep time (sleep duration), sleep efficiency, wake after sleep onset (WASO), and number of awakenings (NOA). A score of ≤ 90% sleep efficiency assessed using actigraphy indicates poor sleep quality.²³

Cognitive performance was assessed using the Continuous Performance Test (CPT) (Conners CPT 3™)²⁴ which is a test of sustained attention and the Trail-Making Task (TMT) from Delis-Kaplan Executive Function System (D-KEFS)²⁵ which is a test to assess executive functioning. For the CPT, participants were seated in front of a computer screen and instructed to press the space bar when any letter of the alphabet except the letter X appeared on the monitor. Participants were instructed to “respond as quickly as possible but also as accurately as possible.” The test takes 14 minutes to complete with no rest provided. The main outcomes were hit reaction time (measured in milliseconds), detectability (the ability to discriminate between targets and non-targets), omissions (missed targets), and commissions (incorrect responses to non-targets). Omissions are an indicator of inattentiveness, and commissions can indicate inattentiveness (if coupled with slow reaction times) or impulsivity (if coupled with fast reaction times).

Participants were instructed to perform the TMT as quickly and as accurately as possible. They used a paper and pencil to “connect the dots” for three conditions: number sequences (1-2-3-4…16; Condition 1), letter sequences (A-B-C-D…P; Condition 2), and number-letter sequences (1-A-2-B-3-C..16-P; Condition 3). Conditions 1 and 2 were used to ensure the participant understood the directions. Only Condition 3 was used for data analysis.

Participants also provided demographic information including sex, age, number of hours of work/week, number of roommates, number of pets, and number of alcoholic drinks/week (Table 1).

Table 1.

Demographic information

Variable	N
Sex
Male	10
Female	40
Number of Roommates
0	4
1	23
2–3	20
4–5	3
Number of Pets
0	33
1	11
2	4
3	1
6	1
Number of Hours of Work/Week
0	12
1–10	19
11–20	14
21–30	5
30+	0
Number of Alcohol Drinks/Week
0	4
1–2	25
3–4	11
5–6	5
7–8	5

Data analysis was performed by using SPSS 22 software (SPSS Inc., Chicago, IL, USA), and the significance level was set at 0.05. Spearman’s correlations were used to examine associations between SHI, PSQI, CPT outcomes, and TMT. Post-hoc Mann-Whitney and Kruskal-Wallis tests were conducted to examine group differences between sleep outcomes (PSQI, SHI) and cognitive performance (CPT outcomes and TMT) for demographic variable categories including sex (male, female), number of roommates (0, 1, ≥2 roommates), number of pets (0, 1, ≥2 pets), number of hours of work/week (0, 1–10, 11–20, 21–30 hrs/week), and number of alcoholic drinks/week (0, 1–2, ≥3).

Results

Forty females and 10 males participated in this study (average age 24.18 years old, SD 1.6; Table 1). The majority of participants reported having a roommate (n = 46; 92%) and did not have a pet (n= 33; 66%). Most reported working part-time (n = 38; 76%) with the most common number of hours of work/week being 1–10 hours/week (n = 19; 38%) followed by 11–20 hours/week (n = 14; 28%). The majority reported consuming alcohol (n = 46; 92%) with the most common amount being 1–2 drinks/week (n = 27; 54%).

Twenty-three participants (46%) scored >5 (range 6–17) on the PSQI, and 27 participants (54%) had ≤ 90% sleep efficiency as assessed using actigraphy indicating poor self-report and objectively assessed sleep quality for nearly half of the participants (Table 2). The average total sleep time (sleep duration) was 479.9 minutes (7.99 hours) with the most common total sleep time being 7–8 hours (n=27; 54%; Table 2).

Table 2.

Sleep characteristics. Data is reported as (Mean±SD) or frequency (n).

Variable	N	Mean ± SD
PSQI		5.6 ± 3.2
≤ 5	27
> 5	23
Sleep Hygiene Index		20.6 ± 6.0
Sleep Efficiency (%)		89.1% ± 4.1%
≥ 90%	23
< 90%	27
Total Sleep Time (min)		479.9 ± 43.3
>8 hrs	2
7–8 hrs	27
6–7 hrs	18
5–6 hrs	3
WASO (min)		47.5 ± 18.9
Number of Awakenings (n)		17.6± 6.9

PSQI: Pittsburgh Sleep Quality Index. WASO: Wake After Sleep

PSQI was not significantly correlated with any of the CPT outcomes or with the TMT (Table 3). SHI was significantly correlated with the CPT outcome detectability (r_s = 0.297, p = 0.036) indicating poorer sleep hygiene is associated with increased errors in discriminating between targets and non-targets. SHI was also significantly correlated with the CPT outcome omissions (r_s = 0.343, p = 0.015) indicating poorer sleep hygiene is associated with an increased inattentiveness. SHI was not significantly correlated with the CPT outcomes of commissions or HRT or with the TMT (Table 3).

Table 3.

Correlation results.

	CPT Detectability	CPT Omissions	CPT Commissions	CPT HRT	TMT
PSQI
rs	0.029	−0.054	0.084	0.108	0.124
p	0.842	0.708	0.562	0.456	0.392
SHI
rs	0.297	0.343	0.162	−0.037	0.162
p	0.036*	0.015*	0.262	0.798	0.261

PSQI: Pittsburgh Sleep Quality Index. SHI: Sleep Hygiene Index; CPT: Continuous Performance Test; HRT: Hit Reaction Time; TMT: Trail-Making Task;

^*indicates p < 0.05

There were no group differences in self-report sleep quality or sleep hygiene between women and men, but women had significantly more omissions on the CPT than men (p = 0.048) indicating greater inattentiveness. There were no group difference in self-report sleep quality or sleep hygiene between the number of pets categories, but there was a significant group difference in CPT detectability (p = 0.029) and CPT commissions (p = 0.038) with the group with one pet having poorer discrimination (detectability) and greater inattentiveness (commissions) than the group with no pets (p = 0.007) and the group with ≥ 2 pets (p = 0.011). There was a significant group difference in number of drinks/week categories on the sleep hygiene index (p = .0.10) with the group that reported consuming 1–2 drinks/week having significantly worse sleep hygiene than the group that reported not drinking (p = 0.031) and the group that reported consuming >2 drinks/week (p = 0.011). There were no group differences on the sleep or cognitive outcomes for the number of roommates categories or the number of hours worked/week categories.

Discussion and Conclusion

This is the first study to describe the sleep duration and sleep quality characteristics of a cohort of DPT students, and these results indicate nearly half of DPT students have poor self-report and objectively assessed sleep quality. This is also the first study to examine the association between self-report sleep quality, sleep hygiene, and cognitive performance. These results suggest poorer sleep hygiene but not self-reported sleep quality is associated with poorer discrimination and inattention. Neither sleep hygiene nor self-reported sleep quality was associated with executive functioning.

Over half (54%) of DPT student reported poor sleep quality and had poor sleep quality assessed by actigraphy. Also, while the majority (n = 29; 58%) obtained on average at least 7 hours of sleep each night which is the recommended amount of sleep for otherwise healthy adults from the American Academy of Sleep Medicine²⁶, 21 participants (42%) obtained less than the recommended hours of sleep. This high prevalence of poor sleep quality and sleep insufficiency is concerning considering the health consequences that are associated with inadequate sleep. Sleep insufficiency has been associated with an increased risk of cardiovascular disease^27,28, obesity^29,30, and Type II Diabetes Mellitus (T2DM).^31,32 Studies have found that both short and long-term sleep durations lead to increased risk for developing depression,^33,34 and increased risk of suicidal behavior.³⁵ Sleeping disorders can also increase an individual’s risk of developing anxiety or other mood disorders.³⁶ Poor sleep quality can also increase an individual’s symptoms of GERD³⁷ and bone diseases such as osteopenia³⁸ and osteoporosis.^39,40

It is interesting that poorer sleep hygiene, but not poorer self-reported sleep quality, was associated with difficulty discriminating and with inattentiveness. This is interesting because other researchers have found that a shorter sleep duration was associated with inattention in elementary school children (ages 7–11) when in the classroom.⁴¹ Another study found that poor sleep quality in undergraduate students was associated with better memory for negative picture recognition and reduced sustained attention for emotionally-neutral pictures.⁴² Perhaps DPT students are less attuned to their sleep quality or perhaps they have more difficulty reporting average sleep quality over the past month due to fluctuations in school assignments, exams and work or school schedules. It is also possible that DPT students can “recover” sleep on the weekends or during lower stress or less demanding times which in turn may affect their perception of sleep quality. A study by Faraut et al.⁴³ found that a 30-minute nap and an extended night of sleep improved alertness in healthy young males after a night of 2 hours of sleep. It is possible that poor sleep quality, or at least the perception of poor sleep quality, is “recovered” in DPT students by using naps or extended nighttime sleep, although future studies are needed to determine this.

Because poorer sleep hygiene was found to be associated with difficulty discriminating and with inattentiveness, it is possible that poorer sleep hygiene could impact academic and clinical performance. Poor sleep hygiene and sleep quality has been associated with poorer academic performance in undergraduate² and medical students.^3,6 Furthermore, poor sleep quality has been associated with increased risk of medical errors.^3,20 Although there are limited studies that have focused specifically on the effects of poor sleep hygiene on academic or clinical performance, these studies do seem to indicate that poor sleep hygiene is associated with lower academic performance^2,3,6 which could potentially impair clinical performance.

It is interesting that neither self-report sleep quality nor sleep hygiene were associated with executive functioning. These results were contrary to our hypothesis that poor sleep quality and sleep hygiene would be associated with poorer executive functioning as a recent meta-analysis indicated that executive function is negatively impacted by impaired sleep.¹⁵ DPT students are generally high-achieving students, both while in the DPT program and also in undergraduate programs, and it is possible that they have learned to compensate for lack of sleep. It is also possible that the TMT test was too short to detect a decrement in executive functioning in this cohort. Future studies should consider determining how sleep is associated with performance during clinical rotations and during clinical decision-making.

The finding that females in this study had greater inattentiveness than males was surprising as prior studies assessing attention in college-age adults failed to find a difference in performance based on sex^44,45. However, the limited number of males in this study makes interpretation of these results difficult. It was interesting that there were no group differences between the number of pets categories for sleep quality or sleep hygiene as pets have been shown to disrupt sleep⁴⁶, although sleep disruption may depend on if the pet sleeps in the bed or not.⁴⁷ Also interesting was that the group with one pet had poorer discrimination and greater inattentiveness than the group with no pets or the group with ≥ 2 pets. It seems likely that pets might impact a person’s ability to maintain attention if the pet is present during testing; however, no pets were present during testing. However, it would seem logical that a larger number of pets might impact attention to a greater extent than a smaller number of pets, which is not what this study found. It should be noted that participants were not asked to provide additional details of the pets, such the type of pet (i.e. dog, cat, fish, etc.), if the pet sleeps in their room or bed, or if the pet belongs to them or their roommate, which could conceivably modulate the impact of the number of pets on sleep or performance on cognitive tests. Also, perhaps there are characteristics of individuals who have a larger number of pets, such as they learn to pay more attention because there are more distractions to attend to. Future studies are needed to investigate these contentions.

It is not surprising that there were group differences on the SHI based on the number of drinks/week categories. The SHI does contain one question concerning consumption of alcohol close to bedtime. However, it would be hypothesized that individuals who reported >2 drinks/week would have the poorest sleep hygiene, which was not the case in this study. Perhaps individuals who report 1–2 drinks/week also engage in other behaviors that interfere with sleep whereas individuals who report >2 drinks/week tend to rely on alcohol to a greater extent than other behaviors, hence a lower score on the SHI. It is plausible that there are other factors that are characteristics to individuals who tend to imbibe in >2 drinks/week which modulate the impact of the number of drinks/week on sleep quality and sleep hygiene as well as performance on cognitive tests. Future studies are needed to investigate these contentions.

It was interesting that there were no group differences on the sleep or cognitive outcomes for the number of roommates categories or the number of hours worked/week categories. It has been shown that an increased household size is associated with insufficient sleep⁴⁸. If there are more people in the house and/or you share a bedroom, there may be more noise or light that interfere with sleep. We did not specifically define “roommate” as sharing a room rather than sharing an apartment or home, so there may have been a difference in interpretation of the definition of “roommate” among participants. It should also be noted that only four participants reported working 21–30 hours/week and no participants reported working more than 30 hours/week. It is likely that the number of hours of work/week was not sufficient to impact sleep or performance on the cognitive tests. However, it seems possible that a greater number of hours/week of work might impact sleep and/or cognitive performance, but additional studies would be needed to assess this hypothesis.

There are several limitations of this study. The sample size was small, which limits the interpretation of the results. Also, all participants attended the same DPT program located in the Midwest, so the results may not generalize to DPT students in other programs. However, this study provides a start to exploring this line of research. Another limitation is caffeine usage was not gathered, which may have influenced level of alertness and, therefore, the results. Only one measure of executive functioning was used in this study, and it may not have been sensitive enough to detect a decrement in performance in this cohort. However, the TMT has also been shown to be a highly sensitive to short term sleep loss.⁴⁹ We also did not assess if testing was done during a more intensive academic week with exams or practicals or if testing was done during a less intensive time. Also, while participants were asked to provide medical histories and a list of medications, it is possible the students were not willing to share sensitive information that may have impacted the results, such as history of depression or anxiety or medication use. Another limitation is that anxiety and depression were not assessed. As prior studies have shown that sleep insufficiency contributes to an increased risk of depression^33,34 and anxiety or other mood disorders,³⁶future studies should consider how depression and anxiety may impact sleep quality, sleep hygiene, and cognitive performance in DPT students.

In conclusion, about half of the participants were identified as having poor sleep quality and poorer sleep hygiene was associated with poorer discrimination and inattention. Also, certain demographic variables may modulate the results. These results could potentially impact the students’ academic and clinical performance as well as their health and wellbeing. Future studies should consider how anxiety, stress, or symptoms of depression may interact with or impact sleep hygiene, sleep quality, and cognitive task performance. Also, additional studies are needed to further assess the influence of demographic variables on sleep quality, sleep hygiene, and cognitive performance.