Environmental risk factors for amyotrophic lateral sclerosis: methodological issues in epidemiologic studies.

The exact role of environmental risk factors in the etiology of the neurodegenerative disease amyotrophic lateral sclerosis (ALS) is still unknown. Their hypothetical contribution ranges from a minimal impact to a major role. Among the environmental factors strictu sensu (i.e., not life-style factors) suspected to play a role in ALS etiology, we consider pesticides, the metalloid selenium, some heavy metals, magnetic fields and cyanobacteria. However, the possibility exists that these factors exert their activity only in genetically susceptible persons and only after long-term exposures, thus further hampering epidemiologic studies. The recent availability of powerful tools such as population-based ALS registries for case ascertainment and clustering detection, and of environmental modeling techniques and of geographical information systems, may yield unique opportunities for offering insight into the etiology of the disease.

Food intake and risk of cutaneous melanoma in an Italian population.

We investigated the association of melanoma risk with food consumption in a northern Italian population in which disease risk was shown to correlate with linoleic acid and soluble carbohydrates intake. We collected information regarding the habitual consumption of 188 food items in 59 patients with newly diagnosed cutaneous melanoma and 59 sex- and age-matched population controls. In the unadjusted analyses, the intake of several foodstuffs directly or inversely correlated with melanoma risk. In multivariate analysis adjusting for several potential confounders, risk correlated directly with vegetable oil intake and inversely with consumption of crispbreads and rusks. Overall, most of the food items rich in linoleic acid and soluble carbohydrates were unrelated to disease risk. Despite the limited statistical precision of the point estimates, these findings seem to indicate that consumption of specific foods may influence melanoma risk.

Adverse health effects of selenium in humans.

Epidemiologic studies and case reports have shown that chronic exposure to selenium compounds is associated with several adverse health effects in humans. An early toxic effect of selenium is on endocrine function, particularly on the synthesis of thyroid hormones following dietary exposure of around 300 micrograms Se/d, and on the metabolism of growth hormone and insulin-like growth factor-1. Other adverse effects of selenium exposure can be the impairment of natural killer cells activity and at higher levels, hepatotoxicity and gastrointestinal disturbances. Dermatologic effects, such as nail and hair loss and dermatitis, occur after exposure to high levels of environmental selenium. Assessing the toxicity and morbidity after long-term exposure to environmental selenium is difficult: neurotoxicity, particularly the degeneration of motor neurons leading to increased risk of amyotrophic lateral sclerosis, might occur after chronic exposure to both organic and inorganic selenium compounds. The results of laboratory investigations and cohort studies suggest that selenium species exhibit a bivalent effect in cancer, either increasing or decreasing risk. Current environmental selenium exposure limits appear to be inadequate for averting adverse health effects.