Possible Effects of the Dietary Supplement Magnesium Compared to Placebo

The questionnaire HealthWatch-11 (HW-11) was utilized with all 11 items: self-rated health, sleep, concentration ability, stress, energy level, control, social support, work efficiency, job satisfaction, workload and work atmosphere. Scale type is verbal rating scale (VRS) for all items (stress and work efficiency use visual analogue scale). The minimum value is 0 and the maximum value is 100 for all items. Higher values mean better outcomes for all variables except for stress and workload, where lower values are better and higher values are worse.

Compliance in the intervention was assessed by counting the number of pills left in the jar. Each jar contained 100 pills at baseline.

Compliance in the intervention was assessed by counting the number of marked days in the compliance calendar.

The questionnaire Oldenburg Burnout Inventory (OLBI) was utilized with 10 items to assess signs of emotional exhaustion and disengagement. Scale type is Likert with 4 steps where the minimum value is 1 and the highest 4. Higher values are worse than lower values (4 items are reversed in coding).

The questionnaire Karolinska Sleep Questionnaire (KSQ) was utilized with 13 items to assess 3 aspects of sleeping problems. Scale type is Likert with 5 steps (minimum value 0 and maximum value 5) where lower values are better and higher values are worse.

The hearing test Pure tone audiogram (PTA) was conducted to establish thresholds for hearing in the frequencies 125 hertz (Hz), 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 3000 Hz, 4000 Hz, 6000 Hz and 8000 Hz. The tests were conducted on each ear separately.

This test was conducted in order to assess hearing in noisy environments. The participant was first asked to establish the Most Comfortable Loudness level (MCL), this was done on one ear only. MCL was established by the participant listening to a recorded male voice saying monosyllabic words in Swedish. The examiner adjusted the loudness level based on the participants' instructions in 5 decibel (dB) steps. Once MCL was established, the speech in noise test was started. The examiner played at set of 25 words per ear with a background noise that was 10 dB lower than the volume of the words. The participant was asked to repeat the words as they heard them. The examiner marked the answers as correct or incorrectly repeated. More correctly repeated words were considered better and more incorrectly repeated words worse. The participant's age is also taken into account since the ability to hear words in a noisy environment declines with age.

Uncomfortable loudness level (UCL) is a test to assess possible sensitivity to sound (hyperacusis). The participant was instructed that they would be hearing a man's voice saying words and that the examiner would increase the volume until the participant experienced the loudness level to start being uncomfortably loud. The maximum sound level was 110 decibel (dB).

The single item "About how many days have you been on sick leave or reported in sick during the past 12 months?" was utilized to assess sick leave. Responses were given on a 5 point Likert scale ranging from 1 to 5, where 1 was better (no sick leave) and 5 was worse (91 days or more of sick leave).

The single item "How many times during the past 12 months have you gone to work despite that you thought you should have been on sick-leave considering your health status?" was utilized to assess sickness presenteeism. Responses were given on a 4 point Likert scale ranging from 1 to 4 where 1 was better (None) and 4 was worse (4 times or more).

Prevalence of pain was assessed using a Likert scale (1=Yes and 0=No). The following 8 body areas were assessed: head, neck, shoulder, arm/hand, upper back, lower back, legs and general pain.

The frequency of pain was assessed utilizing a 4 point Likert scale ranging from 1 to 4 where lower values were better than higher values.

Pain discomfort was assessed utilizing a Visual Analogue Scale (VAS) ranging from 1 to 100 where lower values were better (less discomfort) than higher values (more discomfort).

Pain intensity was assessed utilizing a Visual Analogue Scale (VAS) ranging from 1 to 100 where lower values were better (lower intensity) than higher values (higher intensity).

Functional impairment due to pain was assessed using a Likert scale (1 = Yes and 0 = No) where higher values are worse. Functional impairment was assessed in the following 3 areas: difficulties to carry out your everyday chores due to pain, difficulties to sleep due to pain and difficulties to carry out your work due to pain.