Table 2.

Study characteristics.

Citation Country	Final sample Gender Mean age (final sample) Ethnicity	Predicting variable	Pain-related health outcome	Follow-up duration	Timing of assessments	Adjusted variables	Results: sleep deterioration	Results: sleep improvement
Agmon & Armon (2014) [51] Israel	N = 2131 66% male 46.20 y not stated	Change in self-reported insomnia symptoms from Athens insomnia scale.	Diagnosis of back pain (confirmed through medical records and medical interview with physician)	3.7 y	Predicting variable and pain-related health outcome assessed at three time points spread over a period of 3.7 y.	Age, gender, education, physical activity, self-rated health, smoking, BMI, levels of high-sensitivity C-reactive protein.	Increase in insomnia symptoms from time 1 to time 2 was associated with increased risk of diagnosis of back pain at Time 3 (OR = 1.40 94% CI 1.10–1.71).	None reported.
Campbell et al. (2013) [52] UK	N = 2622 42.1% male Not stated range 50–80+ y not stated	Change in self-reported sleep quality (Jenkins sleep questionnaire).	Self-reported pain presence, persistence, interference and depressive symptoms.	6 y	Predicting variable and pain-related health outcome assessed at three time points (baseline, 3 y and 6 y).	Age, gender, alcohol consumption, smoking, marital status, employment status, and BMI.	New onset of sleep problems associated with increased pain interference and increased risk of depression at follow-up.	None reported.
Ferrie et al. (2013) [36] UK	N = 5003 71.8% male 49.3 y not stated	Change in self-reported sleep quantity.	Immune marker – CRP and IL-6 levels.	5 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, occupation, systolic blood pressure, BMI, total cholesterol, and diabetes.	Decrease in sleep quantity significantly associated with higher IL-6 levels but not CRP at follow-up.	Increase in sleep quantity not significantly associated with CRP and Il-6 levels at follow-up.
Foley et al. (1999) [53] USA	N = 6899 62% male Not stated aged 65+ y not stated	Change in self-reported insomnia symptoms (difficulty falling asleep or early morning arousal).	Diagnosis of hip fracture by physician.	3 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, community (state of residence), income, and education.	New incidence and persistence of insomnia symptoms significantly associated with newly reported presence of hip fracture at follow-up (OR = 2.08 95% CI 1.18, 3.65).	None reported.
Irish et al. (2013) [37] USA	N = 128 63% male 36.45 y 92% white	Change in self-reported sleep quality (PSQI).	Self-report physical symptoms. Immune marker – natural killer cell number and cytotoxicity (n = 51).	12 mo	Two time points. Predicting variable assessed at baseline and follow-up. Pain-related health outcome assessed only at follow-up.	None stated.	Deterioration of sleep quality not significantly correlated with pain-related health outcomes at follow-up.	Improvement in sleep quality not significantly correlated with pain-related health outcomes at follow-up.
Janson et al. (2001) [54] Sweden	N = 2602 100% male Not stated range 30–69 y not stated	Change in self-reported insomnia symptoms (difficulty falling asleep and difficulty maintaining sleep).	Diagnosis of a medical disorder, including joint or low back disorders by physician.	10 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, BMI smoking, physical inactivity, alcohol dependence, and medical disorders.	Increase in insomnia symptoms associated with newly reported medical disorder at follow-up.	None reported.
Komada et al. (2012) [49] Japan	N = 1577 43% male 58.6 y not stated	Change in self-reported sleep quality (Japanese version of PSQI – cut-off score of 5.5 indicating insomnia).	SF36 – PCS	2 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, disease status, alcohol consumption, smoking habits, living status, sleep medication use, CES-D, MCS, PCS, and PSQI scores at baseline.	New incidence of insomnia symptom associated with a decline in PCS scores at follow-up.	Remission of insomnia symptoms not significantly associated with increase in PCS scores at follow-up.
Parthasarathy et al. (2015) [56] USA	N = 1409 45% male 47 y not stated	Change in self-reported insomnia symptoms derived from ICSD insomnia diagnosis criteria.	Immune marker – CRP levels assessed in 722 participants.	6 y	Two time points. Predicting variable assessed at baseline and follow-up. Pain-related health outcome assessed only at 6-y follow-up.	Age, gender, BMI, smoking, physical activity, use of alcohol and medications to get to sleep, marital status, habitual snoring, diabetes mellitus and hypertension.	Persistence of insomnia symptoms associated with an increase in and higher CRP levels at follow-up compared to those with intermittent or no insomnia.	None reported.
Quan et al. (2005) [55] USA	N = 4667 40.9% male 72.3 y not stated	Change in self-reported insomnia symptoms (trouble falling asleep, frequent awakenings and excessive daytime sleepiness).	Diagnosis of arthritis by physician.	1–4 y (mean 3.55)	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, race, time interval between baseline and follow-up examinations.	New incidence of insomnia symptoms associated with report of arthritis in women.	None reported.
Rueggeberg et al. (2012) [38] Canada	N = 157 48.40% male 71.71 y not stated	Change in self-reported sleep quantity using items from PSQI.	Immune marker – diurnal cortisol secretion.	4 y	Predicting variable and pain-related health outcome assessed at three time points (baseline, 2 y and 4 y).	Age, gender, partnership status, education, chronic illness, cortisol-related medication usage, BMI and smoking.	Decrease in sleep quantity associated with significant increases in cortisol secretion level at follow-up.	Increase in sleep quantity not significantly associated with changes in cortisol level at follow-up.
Ropponen et al. (2013) [58] Finland	N = 18,979 47% male 45 y not stated	Change in self-reported sleep quality and sleep quantity.	Diagnosis of back pain by physician and included in national register database on disability pension due to low back pain diagnosis.	23 y	Two time points. Predicting variable assessed at baseline and follow-up. Pain-related health outcome assessed only at follow-up.	Age, education, socioeconomic status, marital status, BMI, physical activity, musculoskeletal pain locations, smoking, alcohol, life satisfaction, use of hypnotic agents, diurnal type, and type of work.	Deterioration and persistent of poor sleep quality associated with higher risk of low back pain diagnosis at follow-up (HR = 1.84 95% CI 1.01–3.37). No association with decrease in sleep quantity.	Improvement in sleep quantity and quality not associated with risk of low back pain diagnosis at follow-up.
Shakhar et al. (2007) [39] USA	N = 45 0% male 39.7 y 47% white 40% black	Change in self-reported sleep quantity.	Immune marker – NKCA levels.	1 mo	Two time points. Predicting variable and pain-related health outcome assessed at both baseline and follow-up.	POMS Depression and Tension subscales scores.	Decrease in sleep quantity not associated with NKCA levels at follow-up.	Increase in sleep quantity was significantly related to an increase in NKCA levels at follow-up.
Silva et al. (2009) [40] USA	N = 3078 45% male 67.3 y 75% white	Change in self-reported insomnia symptoms (difficulty initiating and maintaining sleep, daytime sleepiness).	SF36 – PCS.	5 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, BMI, smoking, sleeping pill use, PSG total sleep time, baseline coronary heart disease and respiratory disease.	Deterioration of insomnia symptoms was not associated with PCS scores. Increase in daytime sleepiness was associated with decline in PCS scores at follow-up.	Improvement of insomnia symptoms not significantly associated with PCS scores at follow-up.
Smagula et al. (2016) [57] Singapore	N = 8265 41.05% male 64.59 y 98.6% asian	Change in self-reported sleep quantity.	Diagnosis of arthritis by physician and diagnosis of hip fracture recorded on hospital database.	12.7 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, baseline sleep duration.	No association between change in sleep and arthritis. Increase in sleep quantity from 6 to 8 to >8 h was linked with greater risk of hip fracture at follow-up (OR = 1.52 95% CI 1.16–2.00).	None reported.
Suh et al. (2014) [41] Korea	N = 1247 40.1% male 54.3 y not stated	Change in self-reported insomnia symptoms (difficulty initiating and maintaining sleep, early morning awakenings and unrefreshed in the morning).	SF36 – PCS.	2 y	Predicting variable and pain-related health outcome assessed at three time points spread over 2 y.	Age, gender, marital status, employment, smoking, alcohol, hypertension, diabetes, depression, PSQI and BMI score.	Deterioration and persistence of insomnia symptoms associated with significantly lower PCS scores at follow-up.	None reported.
Zhang et al. (2012) [42] Hong Kong	N = 2291 50% male 46.3 y not stated	Change in self-reported insomnia symptoms (non-restorative sleep).	Subjective physical health status. Diagnosis of arthritis and other chronic pain condition by physician.	5 y	Predicting variable and pain-related health outcome assessed at two time points (baseline and follow-up).	Age, gender, education, family income, medication, and comorbid sleep problems (insomnia subtypes, habitual snoring, short sleep duration).	New incidence of insomnia symptoms significantly associated with higher risk of reporting a chronic pain condition at follow-up (OR = 2.47 95% CI 1.30–4.69)	Remission of insomnia symptoms associated with a relatively lowered risk of developing a chronic pain condition at follow-up (OR = 1.23, 95% CI 0.57–2.59).

BMI: body mass index, CES-D: center for epidemiological studies depression scale, CI: confidence interval, CRP: creatinine reactive protein, HR: hazard ratio, ICSD: international classification of sleep disorders, IL-6: interleukin-6, MCS: mental component summary, NKCA: natural killer cell activities, OR: odds ratio, PCS: physical component summary, POMS: profile of mood states, PSG: polysomnography, PSQI: Pittsburgh sleep quality index.