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Table 1 Descriptions and definitions of variables

From: Vitamin D levels appear to be normal in Danish patients attending secondary care for low back pain and a weak positive correlation between serum level Vitamin D and Modic changes was demonstrated: a cross-sectional cohort study of consecutive patients with non-specific low back pain

Variable Provision of data and definition
The variables markedahave been extracted from the SpineData database at The Spine Centre of Southern Denmark
Vitamin D level Measured by blood sample: Serum 25-Hydroxyvitamin-D specified in nmol/L
Results divided into 3 groups: (1) normal Vitamin D level > 50 nmol/L, (2) mild Vitamin D deficiency between 25–50 nmol/L, and (3) severe/moderate Vitamin D deficiency < 25 nmol/L [14]
Levels were measured in March, April and May 2011
Body mass index, BMI a Calculated from self-reported height (h) and weight from the database.
Formula: BMI = mass (kg)/height2 (m)
Low Back Pain, LBP a Pain intensity, (0–10 numerical rating scales). Self-reported from the database.
Patients were asked to enter: (1) back pain now, (2) worst back pain last two weeks and (3) average back pain last two weeks.
LBP intensity is an average of the three entered scores [25]
Leg paina Pain intensity, (0–10 numerical rating scales). Self-reported from the database.
Patients were asked to enter: (1) leg pain now, (2) worst leg pain last two weeks and (3) average leg pain last two weeks.
  Leg pain intensity is an average of the three entered scores [25].
Modic changes Defined as signal changes in the vertebral end plates diagnosed on MRI [26] (Jensen, 2007). Data obtained from MRI descriptions.
Modic changes were divided into groups: (1) No modic, (2) Modic Type 1, (3)
Modic Type 2 and (4) Modic Types 1 and 2
Weakness in legs a Patients were asked about any weakness in the legs. Self-reported from the database (yes/no)
Paresthesia in legs a Patients were asked about any paresthesia in the legs. Self -reported from the database (yes/no)
Widespread pain a Patients reported their pain on a pain chart. In the database, the chart is divided into 46 different pain sites, which enables the database to calculate the number of pain regions
  1. a Patients completed an electronic version of the SpineData questionnaire which included a number of questions relevant to the current LBP episode: Pain (now, worst and average) the last two weeks, pain days per week, symptoms in the legs, previous back/neck pain, date of onset and the triggering factor of present pain, function (Roland Morris Disability Questionnaire), quality of life (EuroQOL-5D), general health (0–100 EuroQOL health thermometer, work situation and the use of medication). All data are self-reported.