Low dose mercury and heart rate variability among community residents nearby to an industrial complex in Korea.
BACKGROUND
The effect of mercury on the cardiovascular system has been recently reported, but the mechanisms and its nature, especially in low dose ranges, still need to be confirmed. In this cross-sectional study, the hair mercury was analyzed in relation to the cardiac autonomic activity among community residents nearby to an industrial complex in Korea.


METHODS
A hair sample was obtained from the occiput and was analyzed using a DMA-80 (Milestone, Italy) mercury analyzer. We measured cardiovascular risk factors, including serum total cholesterol, serum triglyceride, HDL cholesterol, systolic and diastolic blood pressure, body mass index (BMI), past history of hypertension, diabetes, and dyslipidemia as potential confounders. As an end point, heart rate variability was assessed for 5 min, in time and frequency domains, using SA-3000P (Medi-core, Korea). For the time domain, standard deviation of the NN intervals (SDNN) was measured. For the frequency domains, very low frequency (VLF, <or=0.04 Hz), low frequency (LF, 0.04-0.15 Hz), high frequency (HF, 0.15-0.4 Hz), total power (TP, approximately <or=0.4 Hz), LF/HF ratio, LF norm (LF/LF+HF), and HF norm (HF/LF+HF) were measured. The association between hair mercury concentration and heart rate variability was assessed after controlling for covariates, including age, gender, socioeconomic status, and other relevant cardiovascular risk factors.


RESULTS
In total, 1589 subjects with a mean age of 33 years (range: 5-83) were included in the final analysis. Hair mercury concentration ranged from 0.01 to 13.36 ppm with a geometric mean of 0.83 microg/g. The hair mercury level was elevated for males, adults, and fish (especially sashimi) consumers, and higher household income group. When age was categorized into decades and analyzed separately, mercury significantly reduced HF measure in the second decade of age in Siwha area (beta=-0.193, p=0.0469) and in the first decade of age in Banwol area (beta=-0.520, p=0.0129). HF parameter decreased by 8.4% [95% confidence interval: 2.2-15.1%] with an 1 ppm increase in hair mercury concentration after adjusting for other selected variables in the multiple linear regression analysis.


CONCLUSIONS
The results suggest that mercury may affect the cardiac autonomic activity through parasympathetic dysfunction even at low exposure levels.
Lim
Sinye
S
Department of Occupational and Environmental Medicine, College of Medicine, Kyunghee University, Seoul, Republic of Korea.
Chung
Hee-Ung
HU
Paek
Domyung
D
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001794:Blood Pressure; D002318:Cardiovascular Diseases / Q000209:etiology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D004562:Electrocardiography; D005260:Female; D006197:Hair / Q000378:metabolism*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D007221:Industry; D007723:Korea; D008297:Male; D008628:Mercury / Q000378:metabolism*; D008875:Middle Aged; D012044:Regression Analysis; D012111:Residence Characteristics; D012307:Risk Factors; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
D008628:Mercury