Background: Sleep quality is a key determinant of physical and mental health, with important implications for immune regulation, psychological well-being, and overall quality of life. In systemic lupus erythematosus (SLE), sleep disturbances are highly prevalent and have been associated with poorer clinical and psychosocial outcomes. However, the specific contribution of potentially modifiable behavioral and environmental factors to sleep quality in this population has been insufficiently investigated.
Objectives: To analyze the association between modifiable lifestyle, behavioral, and environmental factors and sleep quality in adults with systemic lupus erythematosus.
Methods: A multicenter cross-sectional observational study will be conducted. Approximately 250 adults with systemic lupus erythematosus from different regions of Spain will be included. The primary outcome will be sleep quality, assessed using the Pittsburgh Sleep Quality Index (PSQI). Independent variables will include physical activity (International Physical Activity Questionnaire-Short Form), substance use, sleep timing and regularity, napping habits, screen exposure, and bedroom environmental conditions. Secondary variables will include risk of obstructive sleep apnea (STOP-Bang questionnaire), daytime sleepiness (Epworth Sleepiness Scale), perceived stress (Perceived Stress Scale-10), as well as clinical, sociodemographic, and anthropometric variables.
Expected results: To identify behavioral and environmental factors independently associated with poor sleep quality in individuals with systemic lupus erythematosus and to estimate the prevalence of poor sleep quality in the study sample.
Adults aged ≥18 years;
A medical diagnosis of systemic lupus erythematosus (according to current clinical classification criteria);
Both sexes;
Clinically stable condition during the previous 3 months; and
Individuals whose usual occupation involves night or rotating shift work;
A previous diagnosis of a primary sleep disorder receiving specific treatment (e.g., severe obstructive sleep apnea treated with CPAP, narcolepsy, or other central sleep disorders); and
Psychiatric or cognitive impairment that may prevent or substantially limit the accurate completion of the questionnaires
Adults with systemic lupus erythematosus
Cohort
Cross-sectional
Adults with systemic lupus erythematosus
Other interventionPatients with systemic lupus erythematosus included in the study will complete validated questionnaires to address the study objectives.
Measurement of sleep quality
The primary variable will be sleep quality assessed using the Pittsburgh Sleep Quality Index (PSQI), a self-administered questionnaire composed of 19 items grouped into seven components. The global score ranges from 0 to 21 points, with scores \>5 indicating poor sleep quality. This instrument has demonstrated adequate psychometric properties in patients with systemic lupus erythematosus.
Measurement of physical activity
The independent variable will be physical activity assessed using the International Physical Activity Questionnaire-Short Form (IPAQ-SF), an instrument that records the frequency, duration, and intensity of physical activity performed during the previous week and allows results to be expressed in MET·minutes/week. According to the criteria established by the World Health Organization, participants will be classified into low, moderate, or high levels of physical activity.
Measurement of caffeine consumption
The independent variable will be caffeine consumption, assessed by recording the average number of daily servings of caffeinated beverages, including coffee, tea, energy drinks, and caffeinated soft drinks. Participants will report the average number of servings consumed per day according to beverage type, as well as the usual time of the last caffeine intake, given that the effect of caffeine on sleep may depend on the timing of consumption. Caffeine intake will be categorized into low, moderate, or high consumption according to standard epidemiological criteria (e.g., \<1 unit/day, 1-2 units/day, ≥3 units/day). For measurement purposes, participants will be asked questions such as: "How many caffeine units do you consume per day? (1 cup of coffee = 1 unit; 1 energy drink = 2 units)" and "At what time do you usually consume your last caffeinated beverage?"
Measurement of alcohol consumption
The independent variable will be alcohol consumption, assessed by recording both the frequency and quantity of alcohol intake. Frequency will be categorized as never, monthly, weekly, or daily. Quantity will be measured in standard drink units (1 drink = 10 g of alcohol), and participants will report the number of units consumed during a typical week. Additionally, participants will be asked about evening or nighttime alcohol consumption, specifically whether alcohol is consumed within the 3-4 hours prior to bedtime, as this timing may influence sleep quality. Example questions include: "How many units of alcohol do you consume in a typical week?" and "Do you usually consume alcohol in the evening or at night?"
Measurement of tobacco consumption
The independent variable will be tobacco consumption, assessed by recording the number of cigarettes smoked per day. Alternatively, smoking status will be categorized as non-smoker, former smoker, occasional smoker, or daily smoker. Participants will also be asked whether they smoke during the hour before going to bed, given the potential stimulating effects of nicotine on sleep. Example questions include: "How many cigarettes do you smoke per day?" and "Do you smoke during the hour before going to sleep?"
Measurement of risk of obstructive sleep apnea
The secondary variable will be the risk of obstructive sleep apnea, assessed using the STOP-Bang questionnaire, a brief self-administered screening tool composed of eight dichotomous items (yes/no). The questionnaire evaluates snoring, daytime sleepiness, observed apneas, hypertension, elevated body mass index, age, neck circumference, and sex. The STOP-Bang has demonstrated high sensitivity for the detection of obstructive sleep apnea across different clinical and population settings and has previously been used in studies involving individuals with systemic lupus erythematosus to estimate the risk of sleep-disordered breathing.
Measurement of relevant comorbidities
The secondary variable will be the presence of relevant comorbidities, including fibromyalgia, depression, and sleep-related breathing disorders. These conditions will be recorded as dichotomous clinical variables (presence/absence) based on information obtained from the patient's medical history and self-report.
Measurement of daytime sleepiness
The secondary variable will be daytime sleepiness assessed using the Epworth Sleepiness Scale (ESS), a self-administered questionnaire designed to estimate the general level of daytime sleepiness. The instrument consists of eight items that evaluate the likelihood of falling asleep in different common daily situations, generating a total score ranging from 0 to 24, with higher scores indicating greater daytime sleepiness. The ESS has demonstrated the ability to discriminate between healthy individuals and patients with different sleep disorders and has shown correlations with objective measures of sleepiness and sleep-disordered breathing.
Measurement of perceived stress
The secondary variable will be perceived stress assessed using the 10-item Perceived Stress Scale (PSS-10), a self-administered questionnaire designed to measure the degree to which situations in one's life are appraised as stressful during the previous month. Each item is scored on a Likert-type scale from 0 to 4, yielding a total score ranging from 0 to 40, with higher scores indicating greater levels of perceived stress. The PSS has demonstrated adequate psychometric properties, including good reliability and validity, and has been shown to correlate with depressive and physical symptoms, life events, and health-related behaviors, supporting its use as a valid measure of perceived stress as an independent construct. Moreover, it has been recently used in studies involving individuals with systemic lupus erythematosus, supporting its applicability in this population.
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