Academic journal article Journal of Health Population and Nutrition

Association between Chronic Exposure to Arsenic and Slow Nerve Conduction Velocity among Adolescents in Taiwan

Academic journal article Journal of Health Population and Nutrition

Association between Chronic Exposure to Arsenic and Slow Nerve Conduction Velocity among Adolescents in Taiwan

Article excerpt

INTRODUCTION

Arsenic is a widely-distributed element in the environment. It is mainly transported into the human body through the intake of seafood or well-water (1). Chronic exposure to arsenic has been associated with various health effects, including internal cancers (2), skin hyperpigmentation and hyperkeratosis (3-4), hypertension (5), diabetes mellitus (6), ischaemic heart disease (7,8), cerebrovascular disease (9), and peripheral vascular occlusive disease (10).

Peripheral neuropathies--acute or chronic--are affected by many factors and are easily induced by occupational injuries (11) and chronic diseases (12,13). Previous reports have found that acute exposure to arsenic is associated with peripheral neuropathy with both axonopathy and demyelination (14-16). Chronic arsenic exposure, in contrast, was not found to be consistently associated with peripheral neuropathy. The different results obtained in previous studies for chronic exposure to arsenic might be due to a small sample size, a lack of consideration regarding the potential influences of chronic diseases and occupational injuries, or an absence of a correlation between peripheral neuropathy and arsenic exposure dosage. Positive (17-19), slightly-positive (20), and negative (21) results have been reported. Results usually appear as a polyneuropathy with symptoms of distal axonopathy and predominant sensory involvement.

Histologic reports for chronic neuropathy relating to arsenic exposure are rare. A study exploring histologic changes on sural nerve biopsy of chronic arsenic neuropathy reported a reduction of both myelinated and unmyelinated fibres associated with axonal degeneration (22). No demyelination of nerve fibres was noted in this study. The histologic discrepancy between acute and chronic arsenic peripheral neuropathy might suggest different mechanisms in their pathogenesis.

Arsenic neuropathy can be detected by the slowing of the nerve conduction velocity (NCV) in an electrophysiological examination. The NCV results may be affected by age, sex, body height (23), body mass index (BMI) (24), body surface temperature (25), occupational injuries, and chronic diseases. In our present study, we chose teenagers, who had similar age distribution and had low possibility of chronic diseases or injuries, as our study subjects. The male gender and taller body height were taken into consideration as these factors may make the NCV slower. After adjusting for sex and height, a dose-response relationship between peripheral neuropathy and inorganic arsenic exposure indices through drinking well-water was investigated among the residents of Lanyang Basin in Taiwan.

MATERIALS AND METHODS

Subjects

Residents living in the Lanyang Basin, a region in northeastern Taiwan, who have been drinking well-water for decades, were used as subjects. Although a tap-water system exists, some residents still use well-water for economic reasons. In our previous study, 8,102 residents (4,056 men and 4,046 women), who were more than 40 years old and who agreed to participate in the study, were interviewed in their homes during October 1991-September 1994 (9). All residents lived in four townships, namely Chiaohsi, Chuangwei, Wuchieh, and Tungshan.

The junior high school located in Chungwei was randomly sampled, where 162 students from Grades 1 and 2, aged 12-14 years, were selected. A detailed illustration of the study and an informed consent paper were given to every student. After obtaining consents from students and their parents, the students were included in the study. The illustrator did not know the arsenic exposure indices of invited students, and the involvement of participants was totally dependent on the agreement they and their parents made on the informed consent paper. One hundred thirty students and their parents agreed to participate in the study and completed the questionnaire, which included requesting information on personal basic data, history of well-water usage, residential and disease history. …

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