Miyuki Shimada

Neurobehavioral effects of prenatal exposure to methylmercury and PCBs, and seafood intake: Neonatal behavioral assessment scale results of Tohoku study of child development

As factors affecting neonatal neurodevelopment, methylmercury, polychlorinated biphenyls (PCBs), and maternal seafood intake reflecting n-3 polyunsaturated fatty acids (PUFAs) are believed to have adverse or beneficial effects, but there are a few reports addressing such factors simultaneously. We carried out a birth cohort study to clarify the effects of these three factors on the Neonatal Behavioral Assessment Scale (NBAS), administered 3 days after birth. In a total of 498 mother-neonate pairs, the total mercury level (median, 1.96microg/g) in maternal hair at parturition and the summation operatorPCB level (45.5ng/g-lipid) in cord blood were analyzed, and maternal seafood intake was estimated using a semi-quantitative food frequency questionnaire. A negative relationship between the hair mercury level and the motor cluster of NBAS was observed, even after adjusting for PCBs, maternal seafood intake, and possible confounders such as maternal age, birth weight, and parity. The summation operatorPCB level was negatively correlated with the motor cluster, but this association was attenuated after adjusting for mercury and the confounders. There was seen to be a positive association between maternal seafood intake and the motor cluster when considering the effects of mercury and PCBs. In conclusion, our data suggest that prenatal exposure to methylmercury adversely affects neonatal neurobehavioral function; in contrast, maternal seafood intake appears to be beneficial. The neurobehavioral effect of prenatal exposure to PCBs remains unclear in our study. Further research is necessary to elucidate interactive effects of methylmercury, PCBs, and n-3 PUFAs, originating from fish, on child neurodevelopment.

Intervention study on cardiac autonomic nervous effects of methylmercury from seafood.

To scrutinize whether the provisional tolerable weekly intake (PTWI, 3.4 microg/kg body weight/week) of methylmercury in Japan is safe for adults, we conducted an intervention study using heart rate variability (HRV) that has been considered to reflect cardiac events. Fifty-four healthy volunteers were recruited and divided into experimental and control groups. The experimental group was exposed to methylmercury at the PTWI level through consumption of bigeye tuna and swordfish for 14 weeks, and HRV parameters were compared between the two groups. In the experimental group, mean hair mercury levels, determined before and after the dietary methylmercury exposure and after 15-week wash-out period following the cessation of exposure, were 2.30, 8.76 and 4.90 microg/g, respectively. The sympathovagal balance index of HRV was significantly elevated after the exposure, and decreased to the baseline level at the end of this study. Still, such changes in HRV parameters were not found in the control group with a mean hair mercury level of around 2.1 microg/g. In conclusion, the PTWI does not appear to be safe for adult health, because methylmercury exposure from fish consumption induced a temporary sympathodominant state. Rather, long-term exposure to methylmercury may pose a potential risk for cardiac events involving sympathovagal imbalance among fish-consuming populations.

Assessment of exposure to methylmercury in pregnant Japanese women by FFQ.

OBJECTIVE To examine whether an FFQ can be used for assessing exposure to methylmercury (MeHg) by estimating MeHg intake from seafood consumption using the FFQ and confirming the accuracy of the estimated value. DESIGN Seafood consumption of pregnant women was assessed using the FFQ. Total mercury (T-Hg) concentrations of maternal red blood cells (RBC) and hair were measured as exposure indices of MeHg. SETTING A prospective birth cohort study, the Tohoku Study of Child Development (TSCD), which has been ongoing since 2001. SUBJECTS The subjects were 609 pregnant Japanese women who were enrolled in the TSCD. RESULTS MeHg intake was estimated from seafood consumption determined using the FFQ and the MeHg concentrations in each type of seafood. The accuracy of the estimated value was confirmed by comparison with T-Hg in RBC and hair. Estimated MeHg intake was 42.3 microg/week, and 43.0 % of that was from large predatory fish. Compared with the Japanese tolerable weekly intake, in total 12.5 % of the subjects exceeded it. T-Hg concentrations in RBC and hair were significantly correlated with estimated MeHg intake: r = 0.325 (P < 0.0001) for RBC and r = 0.305 (P < 0.0001) for hair. CONCLUSIONS Estimated MeHg intake based on the FFQ was significantly associated with T-Hg concentrations in RBC and hair. Although the estimated value involves uncertainties, the FFQ appears to be a useful tool for assessment of exposure to MeHg.

Trends of body mass index distribution in schoolchildren in Sendai, Japan, 1989–2003

SUMMARY Accumulating evidence indicates a strong association between obesity and health problems. Childhood obesity increases the risk of adulthood obesity. Although it is reported that the number of obese children in Japan has increased, it is unclear whether the obesity index distribution pattern has changed. To clarify this distribution pattern, we analyzed the changes in the body mass index (BMI) of primary (6th grade, 12 years old) and junior high (3rd year, 15 years old) schoolchildren in the city of Sendai during the period from 1989 to 2003. Our department has accumulated information on the height and body weight of all the schoolchildren in the city of Sendai. BMI was calculated using both the height and body weight data. The change in median BMI for 15 years had a slightly upward trend every year with both gender and school year. Although the BMI distribution showed that there was little or no change over time in the lower (10th and 25th) percentiles, the increases in the 75th and 90th percentiles were more marked than that in the 50th percentile in primary school children. On the other hand, there was only a small increase in BMI in the 3rd year of junior high school. Our results indicated that the changes in BMI distribution were concentrated at the upper end of the distribution in primary school children. The shifts in the value of high percentiles might be due to effect modification of the corresponding exposure by another environmental exposure or genetic predisposition. It is suggested that the factors causing this change influenced only part of this population, and affected individuals might represent a susceptible subpopulation of the exposed children.: