Focus on Alternative and Complementary Therapies
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Focus Alternat Complement Ther©2005 Pharmaceutical Press
Focus Altern Complement Ther 2008; 13: 05–6
There are two main types of magnets: static or permanent magnets generate the magnetic field by the spin of electrons within the material itself, and electromagnets generate a magnetic field when an electric current is applied. Most magnets sold for health purposes are static magnets of various strengths. They have been incorporated into arm and leg wraps, mattress pads, necklaces, shoe inserts and bracelets1 and are marketed with claims of effectiveness for reducing pain of various origins.2 It has been suggested that about 28% of patients with rheumatoid arthritis, osteoarthritis or fibromyalgia use magnets or copper bracelets for pain relief.3 Our aim was to assess the clinical evidence from RCTs of static magnets for treating pain.
Databases searched from their respective inception to April 2007 were: Medline, Embase, Amed (Allied and Complementary Medicine Database), Cinahl, Scopus, the Cochrane Library and the UK National Research Register. In addition, we hand searched conference proceedings (FACT, 1996–2006), relevant medical journals (specifically Phytomedicine, 1994–2006; Alternative and Complementary Therapies, 1995–2006; and Forschende Komplement㱭edizin Klassische Naturheilkunde, 1994–2006). The bibliographies of all retrieved articles were searched and there were no restrictions on the language of publication. for all relevant trials lacking data, we attempted to contact the corresponding author. We included only trials that were reported as RCTs with a control consisting of non-magnetic placebo or device with weak magnetic field strength and with pain as an outcome measure. There were no restrictions on the condition causing the pain. Methodological quality was evaluated with the Jadad scoring system4 and allocation concealment was assessed using the Cochrane Collaboration’s classification.5 The mean change in pain, as measured on a 100-mm VAS relative to baseline, was defined as the primary endpoint. In the primary analysis, only randomised placebo-controlled trials were assessed on the basis of data from the end of the treatment period. Sensitivity analyses were performed to test the robustness of the overall effect.
Twenty-five trials were included6–30, and all except two RCTs were double-blinded (Tables 1 and 2). Four RCTs assessed patients with peripheral joint osteoarthritis, and three were available for each of low back pain, delayed-onset muscle soreness and foot pain. There was no other condition for which more than two RCTs were available. Four trials6,8,15,29 used weak magnets, below the assumed therapeutic strength (believed to be 30 mT),6 as the control.
Meta-analysis of the nine trials that assessed pain on a 100-mm VAS indicated no significant difference in pain reduction between the magnet and non-magnetic placebo groups [weighted mean difference (WMD) 2.1mm; 95% CI, −1.8 to 5.9; P=0.29, Χ2=9.03, df=8, P=0.34; I2=11.4%].
Differences in the conditions causing the pain and differences in the duration of the intervention contributed to a degree of clinical heterogeneity. A sensitivity analysis, excluding three short-term randomised trials18,26,30 with intervention periods between 45 min and 18 h, suggested no significant difference between the magnet and placebo groups (WMD on a 100-mm VAS 2.9mm; 95% CI, −2.5 to 8.3; P = 0.29; Χ2 = 7.92, df = 5, P = 0.16; I2 = 36.8%). Assessing only musculoskeletal pain conditions with intervention periods between 2 and 4 months6,17,22,27 also suggested no significant difference (WMD 3.5 mm; 95% CI, −5.5 to 12.4; P = 0.45; Χ2 = 7.67; df = 3; P = 0.05; I2 = 60.9%). Across all trials there was evidence of no effect for intervention periods between 30 min and 1 week. Analysis of the 16 trials that assessed pain using various scales suggested significant statistical heterogeneity and these data were therefore considered unreliable (standardised mean difference 0.23mm; 95% CI, 0.04 to 0.42; P = 0.02; Χ2 = 30.77; df = 15; P = 0.009; I2 = 51.2%).
Osteoarthritis was assessed in four double-blind RCTs.6,8,11,12 Two small trials (n = 26 and 43, respectively) reported some positive effects of static magnets relative to placebo and weak magnets.8,11 This finding was confirmed in a larger trial,6 which reported pain reductions (relative to placebo) on the WOMAC and a VAS. In these three trials,6,8,11 treatments lasting 2 to 12 weeks were associated with positive effects, whereas a small study of continuous 24-h magnet treatment12 did not report such effects. Low back pain was assessed in three double-blind RCTs.12,15,26 One suggested beneficial effects relative to a weak magnet,15 whereas the two smaller trials12,26 showed no significant differences relative to placebo. For each of delayed-onset muscle soreness and foot pain, three RCTs could be included. All of these trials reported no significant differences on VASs for pain (relative to placebo) for magnet field strengths between 50 and 245 mT.
Overall, the data suggested no significant effects of static magnets for pain relief relative to non-magnetic placebo. Peripheral joint osteoarthritis was the one condition for which the evidence appeared encouraging. For all other conditions, there was no convincing evidence to suggest that static magnets might be effective for pain relief.
The limitations of our study pertain to the lack of rigour of the original studies, and (although the forest plot indicates overlap of CIs for all studies) to the heterogeneity of the trials. Clinical heterogeneity was evident in differences in the conditions causing pain and in the duration of the interventions. Two post hoc sensitivity analyses exploring these issues confirmed the results of the overall analysis. Another reason for clinical heterogeneity as the variation in magnet strength in the original studies, from 4 to 395mT. Across all trials there was no convincing indication that high-strength magnets performed any better than low-strength magnets.
The success of blinding in magnet and placebo groups was not assessed in 18 of the RCTs. Non-specific effects may have contributed to the observed effects and may even have been the main factor contributing to the findings in some trials. Six trials6,8,9,17,25,27 established that equal proportions of the magnet and placebo groups believed they had been given magnetic devices; the two groups could thus be assumed to have similar expectations of pain relief. In three of 11 trials indicating a beneficial effect,6,8,9 blinding was demonstrated to have been adequate throughout the study. Among the trials of peripheral joint osteoarthritis, two trials6,8 reported adequate blinding. Also, the trials suffered from a lack of adequate allocation concealment. Most of the sample sizes were small, with 17 of the RCTs assessing 50 or fewer patients (Tables 1 and 2). Therefore, the possibility of a type 2 error cannot be excluded. Across all trials with sample sizes above 100 there was no evidence of a convincing effect in favour of magnets.
Static magnets are generally considered safe. Adverse effects are rare, but reddening of the skin on the area of application has been observed.1 Pacemakers, insulin pumps and other devices adversely affected by magnetic fields are considered contraindications for the use of static magnets.1 In conclusion, the evidence does not support the use of static magnets for pain relief, and such magnets therefore cannot be recommended as an effective treatment. For osteoarthritis, the evidence suggests an opportunity for further investigation.
Table 1. Trials included in the meta-analyses
| Authors (year) | Design (quality score), allocation concealment | Condition/syndrome Sample size | Intervention exposure | Control | Pain outcome (quantification method) | Comparison | Results |
|---|---|---|---|---|---|---|---|
| Winemiller et al. (2005)27 | RCT, double-blind, two parallel groups (5), unclear | Foot pain n = 83 | Magnetic insoles (245 mT) | Placebo | Evening foot pain VAS at 4, 8 weeks | Magnet vs. placebo | No significant differences at 4, 8 weeks |
| At least 4 h daily on 4 days per week for 8 weeks | |||||||
| Reeser et al. (2005)30 | RCT, double-blind, two parallel groups (3), unclear | Delayed-onset muscle soreness n = 23 | Magnetic bands to one of each person’s arm (35mT) | Placebo to one of each person’s arm | Muscle pain VAS at day 5 | Magnet vs. placebo | No significant differences |
| 45 min daily for 5 days | |||||||
| Mikesky and Hayden (2005)28 | RCT, double-blind, two parallel groups (2), unclear | Delayed-onset muscle soreness n = 20 | Magnetic bands to one of each person’s arm (75mT) | Placebo to one of each person’s arm | Muscle pain VAS at day 7 | Magnet vs. placebo | No significant differences |
| 7 days continuously | |||||||
| Harlow et al. (2004)6 | RCT, double-blind, three parallel groups (4), unclear | Osteoarthritis n = 193 | Magnetic wrist bracelet (170–200mT) | Placebo | Hip/knee pain | 1a. Magnet vs. placebo | 1a. Significant differences (P < 0.03) |
| During waking hours for 12 weeks | Weak magnet (21–30mT) | 1. WOMAC at 12 weeks | 1b. Magnet vs. weak magnet | 1b. No significant differences | |||
| 2. VAS at 12 weeks | 2a. Magnet vs. placebo | 2a. Significant differences (95% CI, 3.0 to 19.8) | |||||
| 2b. Magnet vs. weak magnet | 2b. No significant differences | ||||||
| Wolsko et al. (2004)8 | RCT, double-blind, two parallel groups (4), adequate | Osteoarthritis n = 26 | Magnetic knee sleeve (4–85mT) | Placebo (0.065 mT) | Knee pain 1. WOMAC at 6 weeks | Magnet vs. placebo | 1. No significant differences |
| 6 h daily for 6 weeks | 2. 5-item combined VAS at 4 h | 2. Significant differences (P = 0.03) | |||||
| Winemiller et al. (2003)17 | RCT, double-blind, two parallel groups (5), unclear | Plantar heel pain n = 101 | Magnetic insoles (245 mT) | Placebo | Foot pain VAS at 4, 8 weeks | Magnet vs. placebo | No significant differences at 4, 8 weeks |
| 16 h weekly for 8 weeks | |||||||
| Weintraub et al. (2003)9 | RCT, double-blind, two parallel groups (5), unclear | Diabetic peripheral neuropathy n = 259 | Magnetic insoles (45mT) | Placebo | Foot pain VAS at baseline, 1, 2, 3, 4 months | Magnet vs. placebo | No significant differences at 4 months |
| 4 months continuously | |||||||
| Brown et al. (2002)10 | RCT, double-blind, two parallel groups (4), adequate | Chronic pelvic pain n = 32 | Magnets secured to pain sites (50mT) | Placebo | Pain at trigger points following abdominal palpation | Magnet vs. placebo | No significant differences |
| Carter et al. (2002)18 | RCT, double-blind, two parallel groups (5), adequate | Carpal tunnel syndrome n = 30 | Magnetic pads (100 mT) 45 min in a monitored setting | Placebo | Wrist pain VAS at 15, 30, 45 min and 2 weeks posttreatment | Magnet vs. placebo | No significant differences |
| Pope and McNally (2002)19 | RCT, double-blind, three parallel groups (3), adequate | Repetitive strain injury n = 45 | Magnetic wrist bracelet (245 mT) | 1. Placebo | Wrist pain Likert scale at 30 min | Magnet vs. placebo | No significant differences |
| 30 min in a monitored setting | 2. No treatment | ||||||
| Segal et al. (2001)20 | RCT, double-blind, two parallel groups (4), adequate | Rheumatoid arthritis n = 64 | MagnaBloc (190mT) | Weak magnet (72mT) | Knee pain VAS at 1 h, 1 day, 1 week | Magnet vs. weak magnet | No significant differences |
| 1 week continuously | |||||||
| Alfano et al. (2001)13 | RCT, double-blind, five parallel groups (5), unclear | Fibromyalgia (n = 119) | 1. Magnetic mattress pad (395 mT) | 1. Placebo | 18 defined pain sites assessed by dolorimetry | Magnet (395 mT) vs. placebo | Significant differences (P = 0.03) |
| 2. Magnetic mattress pad (75mT) | 2. Usual care | FIQ at 6 months | |||||
| 6 months at night | |||||||
| Collacott et al. (2000)26 | RCT, double-blind, crossover (5), unclear | Low back pain n = 20 | Flexible magnet (30mT) 6 h daily for 3 days | Placebo | Lower back pain | Magnet vs. placebo | 1. No significant differences |
| 1. VAS at 18 h | 2. No significant differences | ||||||
| 2. MPQ at 18 h | |||||||
| Colbert et al. (1999)22 | RCT, double-blind, two parallel groups (4), adequate | Fibromyalgia syndrome n = 30 | Magnetic mattress pads (20–60 mT) | Placebo | Body pain VAS at 16 weeks | Within group comparisons (inter-group comparison not provided) | Significant reduction in magnet group (P = 0.04) |
| 16 weeks at night | No significant reduction in placebo group | ||||||
| Vallbona et al. (1997)16 | RCT, double-blind, two parallel groups (4), unclear | Post-polio syndrome (n = 50) | Magnets secured to pain sites (30–50mT) | Placebo | Muscular or arthritic-like pain MPQ at 45 min | Magnet vs. placebo | Significant differences (P < 0.0001) |
| 45 min in monitored setting | |||||||
| Hong et al. (1982)25 | RCT, double-blind, four parallel groups (2), unclear | Neck and shoulder pain (n = 101) | Magnetic necklace (130 mT) | Placebo | Intensity/frequency of pain and stiffness | Magnet vs. placebo | No significant differences |
| 3 weeks continuously | 5-point verbal scale at 3 weeks |
FIQ, Fibromyalgia Impact Questionnaire; MPQ, McGill Pain Questionnaire.
Table 2. RCTs lacking adequate data for meta-analyses*
| Authors (year) | Design (quality score), allocation concealment | Condition/syndrome Sample size | Intervention exposure | Control | Outcome measures | Comparison | Results |
|---|---|---|---|---|---|---|---|
| Eccles (2004)29 | RCT, double-blind, two parallel groups (5), adequate | Dysmenorrhoea n = 35 | Magnetic underwear device (270mT) | Weak magnet (14mT) | Pain MPQ | Magnet vs. weak magnet | Significant differences (P < 0.02) |
| 2 days before to after menses | |||||||
| Kanai et al. (2004)7 | RCT, double-blind, two parallel groups (2), unclear | Frozen shoulder n = 40 | Magnets pasted on pain sites (130 mT) | Placebo | Composite score from spontaneous pain, range of movement, pain to palpation and night pain at 1, 2, 3, 4 weeks | Magnet vs. placebo | Significant differences (P < 0.05) |
| 3 weeks continuously | |||||||
| Hinman et al. (2002)11 | RCT, double-blind, two parallel groups (4), adequate | Osteoarthritis n = 43 | Magnetic discs (40–56mT) | Placebo | Knee pain Sum of VAS ratings at 2 weeks | Magnet vs. placebo | Significant differences (P = 0.002) |
| 2 weeks, worn when pain felt | |||||||
| Holcomb et al. (2002)12 | RCT, double-blind, crossover (2), unclear | Low back pain n = 41, knee osteoarthritis n = 13 | MagnaBloc (200 mT) | Placebo | Back, knee pain VAS at 1, 3 and 24 h | Magnet vs. placebo | No significant differences at 24 h for back or knee pain |
| 24 h continuously | |||||||
| Weintraub (1999)21 | RCT, double-blind, crossover (4), unclear | DPN and N-DPN n = 24 | Magnetic insole (47.5mT) | Placebo | Burning/numbness and tingling 5-point scale at 4 months | DPN vs. N-DPN | No comparison between magnet and placebo magnet |
| 4 months daily | |||||||
| Man et al. (1999)14 | RCT, double-blind, two parallel groups (3), unclear | Suction lipectomy n = 20 | Magnets secured to suctioned areas (15–40mT) | Placebo | Post-operative pain VAS at 1, 2, 3, 4, 7 and 14 days | Magnet vs. placebo | Significant differences (P < 0.05) days 1–7 |
| 14 days continuously | |||||||
| No significant differences at 14 days | |||||||
| Kanai et al. (1998)15 | RCT, double-blind, two parallel groups (3), unclear | Low back pain n = 85 | Magnets pasted on pain sites (180 mT) | Weak magnet (10mT) | Composite score of spontaneous pain, pain in motion, numbness, limitation of range of motion, tenderness and palpable hardenings in the muscles at 1, 2, 3, 4 weeks | Magnet vs. weak magnet | Significant differences at 1, 2, 3, 4 weeks (P < 0.01) |
| 3 weeks continuously | |||||||
| Borsa and Liggett (1998)23 | RCT, single-blind, three parallel groups (1), unclear | Delayed-onset muscle soreness n = 45 | Flexible magnets secured to pain sites (70mT) | 1. Placebo | Muscle pain VAS at 24, 48, 72 h | Magnet vs. placebo vs. no treatment | No significant differences |
| 72 h continuously | 2. No treatment | ||||||
| Caselli et al. (1997)24 | RCT, open, two parallel groups (2), unclear | Plantar heel pain n = 40 | Magnetic insoles (50mT) | Placebo | Heel pain VAS at 4 weeks | Magnet vs. placebo | No significant differences |
| 4 weeks daily |
*adequate data meaning data allowing statistical pooling
DPN, diabetic peripheral neuropathy; N-DPN, non-diabetic peripheral neuropathy
MPQ, McGill Pain Questionnaire; PDI, pain disability index.
