Heavy metallic elements influence AMD progression

By Lucy Piper, Senior medwireNews Reporter

Researchers report associations between age-related macular degeneration (AMD) and five heavy metallic elements, in findings that highlight the detrimental effects of pollution but the possible benefits of essential elements supplementation.

They measured blood concentrations of lead, mercury, cadmium, manganese and zinc, and used logistic regression analyses to assess the association with AMD in 3865 people aged at least 40 years. Of these, 243 had early AMD, with the presence of soft, indistinct drusen or reticular drusen or hard or soft distinct drusen with pigmentary abnormalities, 11 had late AMD including signs of wet AMD or geographic atrophy and the remaining 3611 were free of the condition.

The results, published in Ophthalmology, showed that lead was positively associated with both early and late AMD in all analyses, with odds ratios of 1.12 and 1.25, respectively, while mercury and cadmium were positively associated only with late AMD, at corresponding odds ratios of 1.03 and 2.25. By contrast, manganese and zinc were inversely associated with late AMD, at respective odds ratios of 0.16 and 0.91.

The researchers found a skewed distribution of the five metallic elements in the blood, but despite this the logistic regression analyses gave similar results for nontransformed and logarithmic-transformed blood concentrations for each metallic element.

Commenting on their findings, Kyu Hyung Park (Seoul National University Bundang Hospital, South Korea) and colleagues suggest that because lead was associated with both early and late AMD, its toxic mechanism “may be different from and more extensive than those of other metallic elements”, and call for further investigation of these mechanisms.

They also note that cadmium was associated with late AMD even after adjusting for smoking, which can significantly increase the effects of cadmium on the body, suggesting a causal involvement.

“Cadmium may facilitate development and/or progression of AMD by increasing oxidative stress, promoting lipid peroxidation, and producing inflammatory cytokines”, they explain. It may also interfere with zinc and manganese binding, both of which are involved in decreasing oxidative stress. Indeed, both of these essential heavy metals had a protective effect on late AMD.

“The results suggest that the toxic heavy metals (lead, mercury, and cadmium) may negatively influence AMD, whereas essential heavy metals (manganese and zinc) may favorably influence AMD”, the researchers conclude.

As such, “[e]nvironmental and industrial pollution should be highlighted in view of public health and eye diseases”, they say. “In addition, biomedical researchers should pay more attention to deficiencies of and supplementation with these essential elements.”

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