Identification of Modifiable Sleep-related Factors in Patients With Systemic Lupus Erythematosus.

• Adults with systemic lupus erythematosus (Other): Patients with systemic lupus erythematosus included in the study will complete validated questionnaires to address the study objectives.

Primary outcomes

• Measurement of sleep quality [Screening visit]: 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.

Secondary outcomes

• Measurement of physical activity [Screening visit]: 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 [Screening visit]: 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 [Screening visit]: 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 [Screening visit]: 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 medications affecting sleep [Screening visit]: The independent variable will be the use of medications that may affect sleep, including hypnotics, anxiolytics, antidepressants, and stimulants. Participants will be asked whether they take any of these medications, which specific drugs they use, and the timing of administration. This variable will be primarily categorized as dichotomous (yes/no), and additional information may be collected regarding the pharmacological class and whether the medication is taken under medical prescription or through self-medication. Example questions include: "Do you take any medication to help you sleep, for anxiety, depression, or to stay awake? Please indicate which ones." and "Do you usually take these medications at night?"
• Measurement of sleep schedule (sleep-wake rhythm) [Screening visit]: The independent variable will be sleep schedule, assessed by recording participants' usual bedtime and wake-up time. Information will also be collected regarding potential variability between weekdays and weekends to evaluate the regularity of the sleep-wake rhythm. Example questions include: "What time do you usually go to bed on weekdays?" and "What time do you usually wake up on weekends?"
• Measurement of sleep regularity (variability in sleep schedule) [Screening visit]: The independent variable will be sleep regularity, assessed by evaluating the variability in habitual sleep schedules across different days of the week. Participants will be asked whether their usual bedtime varies by more than one hour between days, a criterion commonly used in circadian rhythm research. This variable will be recorded as a dichotomous measure (yes/no). Example question: "Does the time at which you usually go to bed vary by more than one hour across different days of the week?"
• Measurement of napping habits [Screening visit]: The independent variable will be napping habits, assessed by recording the weekly frequency and typical duration of daytime naps. Nap duration will be categorized into standard intervals commonly used in sleep research: <30 minutes, 30-60 minutes, and >60 minutes. Participants will be asked questions such as: "Do you take naps? If yes, how often per week?" and "How long do your naps usually last?"
• Measurement of screen use before bedtime [Screening visit]: The independent variable will be screen use during the hour before bedtime, assessed by recording the frequency, type of device, and duration of exposure. Frequency will be categorized as never, less than 2 days per week, several days per week, or daily. Participants will also report the type of device used (e.g., smartphone, computer, television, or tablet) and the typical duration of screen exposure (<30 minutes, 30-60 minutes, or >60 minutes). Example question: "During the hour before going to sleep, do you use screens? Please indicate the frequency and duration of use."
• Measurement of bedroom environment [Screening visit]: The independent variable will be bedroom environment, assessed through self-reported evaluation of environmental conditions during sleep, including light, noise, temperature, and comfort. These factors will be measured using a Likert scale ranging from 1 to 5. Participants will also be asked about the presence of potentially disruptive stimuli in the bedroom, such as the presence of a mobile phone, television, or pets in the bed. Example questions include: "Rate from 1 to 5 how much light is present in your bedroom while sleeping." and "Are there frequent noises during the night?"
• Measurement of pre-sleep stress or cognitive arousal [Screening visit]: The independent variable will be pre-sleep stress or cognitive arousal, assessed by asking participants about the presence of stress, worry, or intrusive thoughts during the period before bedtime. This variable will be measured using a Likert scale ranging from 1 to 5, where higher scores indicate greater levels of stress or cognitive activation prior to sleep. Example question: "During the hour before going to sleep, how often do you experience stress, worry, or mental rumination?"
• Measurement of pre-sleep activities [Screening visit]: The independent variable will be pre-sleep activities, assessed by recording the frequency of behaviors performed before bedtime that may negatively or positively influence sleep. Participants will report the frequency (never, rarely, sometimes, often, always) of specific activities, including heavy evening meals, vigorous nighttime physical exercise, hot showers or relaxation rituals, and relaxing activities such as reading, meditation, or listening to soft music.

Other outcomes

• Measurement of risk of obstructive sleep apnea [Screening visit]: 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 [Screening visit]: 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 [Screening visit]: 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 [Screening visit]: 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.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* 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
* Provision of written informed consent.

Exclusion Criteria:

* 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