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

Measurement of sleep hygiene

The independent variable will be sleep hygiene assessed using the Sleep Hygiene Index (SHI), a self-administered questionnaire composed of 13 items designed to evaluate the presence of behaviors associated with inadequate sleep hygiene. Each item assesses the frequency with which participants engage in specific sleep-related behaviors using five response options (always, frequently, sometimes, rarely, and never). The items of the SHI are derived from the diagnostic criteria for inadequate sleep hygiene described in the International Classification of Sleep Disorders. The total score is calculated by summing all items, providing a global measure of sleep hygiene, with higher scores indicating more maladaptive sleep habits.

Time frame: Screening visit

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.

Time frame: Screening visit

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?"

Time frame: Screening visit

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?"

Time frame: Screening visit

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?"

Time frame: Screening visit

Measurement of medications affecting sleep

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?"

Time frame: Screening visit

Measurement of sleep schedule (sleep-wake rhythm)

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?"

Time frame: Screening visit

Measurement of sleep regularity (variability in sleep schedule)

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?"

Time frame: Screening visit

Measurement of napping habits

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?"

Time frame: Screening visit

Measurement of screen use before bedtime

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."

Time frame: Screening visit

Measurement of bedroom environment

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?"

Time frame: Screening visit

Measurement of pre-sleep stress or cognitive arousal

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?"

Time frame: Screening visit

Measurement of pre-sleep activities

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.

Time frame: Screening visit