Researchers have found links between several heavy metals and scleroderma, a discovery that prompted them to encourage doctors to check whether their patients had occupational exposure to heavy metals.
Interestingly, some metals were associated more with male scleroderma patients and some with females.
The study, “Systemic sclerosis and exposure to heavy metals: A case control study of 100 patients and 300 controls,” was published in the journal Autoimmunity Reviews.
With increasing evidence that environmental factors may contribute to scleroderma, researchers at the Rouen University Hospital and the Institute for Biochemical Research, Rouen in France noted that previous studies had failed to explore whether heavy metals contributed to scleroderma.
The research team measured heavy metals in the hair of 100 scleroderma patients and 300 healthy controls.
To make comparisons more informative, they matched each patient with three controls of the same age, gender, and smoking habits. None of the patients had other autoimmune diseases.
The team gathered information on occupations and recreational activities that might have exposed the participants to heavy metals.
Since patients and controls came from the same geographical area, researchers assumed that any exposure to heavy metals from diet would be the same from person to person.
Hair is better suited for analyses of heavy metals than blood samples. Metal levels in blood can be high, then decrease. Hair stores higher amounts of metal so it’s a better barometer of historical exposure to the substances. To avoid differences caused by hair length, the samples consisted of the 3 centimeters of hair closest to the skin.
The patient group was 78 women and 22 men.
Analyses showed that the scleroderma patients had higher median levels of antimony, cadmium, lead, mercury, molybdenum, palladium, and zinc than controls. Patients had lower levels of germanium and silver.
Women with scleroderma had higher median levels of antimony, cadmium, lead, mercury, palladium, and zinc than female controls. In contrast, male patients had higher levels of only antimony and platinum, compared with male controls.
The differences could likely be traced to the participants’ occupations, the researchers said.
“In the present case-control study, we have . . . shown a marked association between SSc [systemic sclerosis] and antimony exposure. Interestingly, we have found a significant association between SSc and antimony exposure in both male and female patients.” the team wrote. “Antimony is released in: 1) producing of semi-conductors, infrared detectors and diodes, lead storage batteries, solder, sheet and pipe metal bearings, castings, pewter, metal alloys, fire-retardant formulations for plastics, rubbers, textiles, paper and paints, explosives; and 2) manufacturing of electronics.”
The human biological mechanisms through which antimony may contribute to the development of scleroderma remain unclear, however, the research team said.
“Another main finding in our case-control study is that we have shown a marked association between SSc and cadmium exposure. The current study interestingly shows that the association between SSc and cadmium exposure was stronger in females than in males. In our experience, exposure to cadmium was observed in patients producing batteries, pigments, coatings and platings, stabilizers for plastics and nonferrous alloys, photovoltaic devices,” the team wrote. “The pathogenic mechanisms of cadmium remain unknown in the development of SSc.”
Researchers also found an association between female scleroderma patients and exposure to lead, mercury, palladium and zinc. They believe the differences in exposures between male and female patients reflect differences in their occupations.
“The present study shows a marked correlation between SSc and exposure to antimony, cadmium, lead, mercury, molybdenum, palladium and zinc. Thus, occupational exposure should be systematically checked in all SSc patients at diagnosis. Finally, the association between SSc and occupational exposure may be variable according to patients’ gender,” the team concluded.
For the majority of these metals, little is known about how they can trigger autoimmune processes.