Repetitive Strain Injury (RSI) and Magnesium and Fluoride Intake

by G.E. Smith (New Zealand Medical Journal, 98:556-557, 1985)


Repetitive strain injury (RSI), a "new" clinical syndrome, is characterized chiefly by a severe pain in wrists, forearms, hands and fingers. Although to date, the cause and pathogenesis of RSI is obscure, it is clearly related to frequent physical stresses; it seems to involve, mainly, musculoskeletal structures.

In 12 RSI subjects fluoride (F-) levels in bone were appreciably higher than 12 appropriate controls. Estimate of dietary intake of RSI subjects, revealed a Mg2+ deficit and an excessive F- intake. Fluorotic bone has an increased Mg2+ content possibly due to some deposition of MgF2. The amorphous phase in bone may act as a "reservoir" of ions available to regulate plasma Ca, PO4 and Mg2+ levels. Fluoride accumulates in bone with age, especially in areas of active ossification. A locally raised F- concentration in an osteocyte lacunae (during resorption) could interfere with normal functioning of the cell, or trigger the precipitation of crystalline apatite, or lead to the formation of MgF2. Any one of these reactions might interfere with the passage of Mg2+ ions from the bone "reservoir" into circulating extracellular fluid. A localized Mg2+ deficiency could disturb pyrophosphate metabolism and lead to deposition of Ca salts in sensitive areas.

Through adjustment of dietary intake of the previously mentioned 12 RSI subjects which included more Mg2+ and less F-, eight of the subjects experienced market relief from previously painful RSI symptoms after a six week test period.

In a letter to the editor Dr. Smith stated (New Zealand Medical Journal, 28 August, 1985, page 710):

Chronic fluoride intoxication may play a role in the aetiology of at least some cases of so-called repetitive strain injury. Data obtained in a recent pilot study in Melbourne, where the very soft water has been fluoridated for sever years, support the hypothesis. In the study, specimens were obtained from alveolar bone after tooth extraction. The mean fluoride concentration of bone in subjects with RSI (2737 ppm F) was greater (p=0.0001) than the mean (1687 ppm F) in those who did not complain of that condition.

While it has been known for many years that an excessive daily intake of fluoride may lead to deleterious effects on musculoskeletal structures, the question of the lower toxic fluoride content of bone has yet to be answered. Roholm suggested that normal bone contains 900 ppm fluoride (range 600-2100 ppm F).

Early bone flurosis is not clinically obvious, and cases often involve young adults whose only complaints are vague pains in the small joints of the hands and feet, and lower back. Such cases may be misdiagnosed as rheumatoid arthritis or ankylosing spondylitis. As fluoride continues to accumulate in bone radiologically detectable changes may be diagnostic and these include: calcification along tendons, fascial and muscular attachments, particularly the interosseous membranes of the forearms and legs. It seems reasonable to assume that before x-ray detectable deposits build-up in these tissues, microcrystals or hydroxyapatite must be present. Tendinitis and bursitis are occasionally associated with periarticular deposits of hydroxyapatite. The condition has been called, "calcific periarthritis" and often mimicks acute arthritis.

Schumacher et all have suggested that apatite crystals, present in joint effusions in a variety of situations, should be considered as possibly responsible for several clinical syndromes. They have also shown that apatite crystals can trigger an acute inflammatory response. Therefore, it is conceivable that some cases of RSI might result from deposition of apatite crystals in and around synovial sheaths and tendons passing through the carpal tunnel.

The posibility that some individuals are now receiving too much fluoride merits serious attention. The US National Research Council has tenatively recommended as safe for adults an intake of 1.5-4.0 mg fluoride per day. However, people are now exposed to fluoride in a multiplicity of everyday sources, and Marier, of the Canadian National Research Council, believes that fluoride intake in fluoridated areas is now 5 mg or more fluoride per day.