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Methylmercury in colostrum and milk of Japanese mothers
Chemosphere 137 (2015) 221
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Letter to the editor Methylmercury in colostrum and milk of Japanese mothers
Iwai-Shimada et al. (2015)’s paper on the transfer of maternal methylmercury (MeHg) through milk lipids is a significant contribution to health and environmental sciences. This team gathered unique data related to Hg chemical species and human milk; however, a few conceptual and methodological questions need addressing. Although fish is the main MeHg carrier, the Japanese diet is also rich in rice that in China has been shown to contain MeHg (Rothenberg et al., 2013). There are few papers reporting MeHg concentrations in breast milk, especially in populations with elevated fish consumption; therefore, it is important to reference and discuss studies of high fish-consumption mothers. Iwai-Shimada et al. cited only European studies, missing a high fish-consumption study in the Amazon (Vieira et al., 2013). Vieira et al. (2013) investigated MeHg in breast milk of urban and rural mothers who, like Japanese women, consume fish as ‘‘staple foods’’. Although urban mothers showed a comparatively lower hair-Hg (1.32 lg/g) concentration, subsistence mothers had more than double the hair-Hg concentrations (8.24 lg/g) reported by Iwai-Shimada et al.’s study (3.43 lg/g). Fish consumption (reflected by hair-Hg) is an important point of comparison because the proportion of MeHg:THg in breast milk was respectively 37% and 12% for riverine and urban mothers (Vieira et al., 2013); these variations are comparable to those discussed by Iwai-Shimada et al. in Mediterranean mothers, indicating unaccounted factors associated with maternal MeHg transfer. Furthermore, in agreement with the study by IwaiShimada et al., Vieira et al. (2013) did not find a significant correlation between THg concentrations in milk and either maternal amalgam filling or daily fish consumption; nor did they find any statistically significant correlation between total hair-Hg concentration and total milk-Hg concentration or between MeHg in hair and in milk samples (Vieira et al., 2013). The unique feature of Iwai-Shimada et al.’s paper (MeHg and lipids) does not address issues central to understanding total lipids in human lactation, such as stage of lactation and type of sampling. Iwai-Shimada et al. inform us that ‘‘maternal hair and breast milk were collected two days and one month after delivery’’, yet they did not differentiate ‘colostrum’ (two-day sample) when reporting ‘breast milk’ in tables, graphs, and statistical analysis. The early post-natal mammary secretion has special physical–chemical and functional characteristics, and for that is called colostrum; this early secretion changes substantially in lipids and protein concentrations as it matures into ‘milk’ (Macias and Schweigert, 2001). Not only that, but milk fat also changes significantly between fore- and hind-milk (Dórea et al., 1982). Iwai-Shimada referenced Bjornberg et al. (2005) showing that total Hg decreases from colostrum to mature milk, but they http://dx.doi.org/10.1016/j.chemosphere.2015.06.100 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.
did not discuss this opposite trend in relation to milk lipids. Therefore, it is crucial to describe how colostrum and milk were collected and accounted for in relation to MeHg concentrations. There is need for adjustments related to the estimated ‘‘lactational exposure to MeHg in one-month-old infants’’; a ‘‘body weight of 4.0 kg’’ was assumed along with ‘‘an average daily milk consumption of 800 mL’’, which may overestimate milk intake. Grandjean et al. (1994) recommend 125 mL/kg body weight/day, which would give a daily milk intake of 600 mL. Additionally, it is not clear if the ‘lactational exposure’ MeHg represents one or two samples (colostrum or mature milk). Thus, differences in milk lipids between colostrum and mature milk, as well as daily colostrum (first 10 days) based on milk consumption rate per body weight may result in less MeHg transfer during the first month of breastfeeding. Another issue deserving attention is related to ‘‘repeated measurement’’ of the samples from the same mother taken on two occasions – two days and one month as stated in the footnotes of Tables 1 and 2 (‘‘Maternal blood and breast milk were collected one day postpartum and one month after delivery, respectively’’); what does ‘‘Breast milk’’ represent? Is it a pooled analysis of two samples? If so, how was it dealt with in the correlation and regression analysis? Because only ‘‘milk’’ sample is referred to, we are not informed if the colostrum (one- or two-day sample) was included in the one-month milk reported. References Bjornberg, K.A., Vahter, M., Berglund, B., Niklasson, B., Blennow, M., SandborghEnglund, G., 2005. Transport of methylmercury and inorganic mercury to the fetus and breast-fed infant. Environ. Health Perspect. 113, 1381–1385. Dórea, J.G., Horner, M.R., Bezerra, V.L., 1982. Correlation between changeable human milk constituents and milk intake in breast-fed babies. J. Pediatr. 101, 80–83. Grandjean, P., Jorgensen, P.J., Weihe, P., 1994. Human milk as a source of methylmercury exposure in infants. Environ. Health Perspect. 102, 74–77. Iwai-Shimada, M., Satoh, H., Nakai, K., Tatsuta, N., Murata, K., Akagi, H., 2015. Methylmercury in the breast milk of Japanese mothers and lactational exposure of their infants. Chemosphere 126, 67–72. Macias, C., Schweigert, F.J., 2001. Changes in the concentration of carotenoids, vitamin A, alpha-tocopherol and total lipids in human milk throughout early lactation. Ann. Nutr. Metab. 45, 82–85. Rothenberg, S.E., Yu, X., Zhang, Y., 2013. Prenatal methylmercury exposure through maternal rice ingestion: insights from a feasibility pilot in Guizhou Province, China. Environ. Pollut. 180, e291e–e298e. Vieira, S.M., de Almeida, R., Holanda, I.B., Mussy, M.H., Galvão, R.C., Crispim, P.T., Dórea, J.G., Bastos, W.R., 2013. Total and methyl-mercury in hair and milk of mothers living in the city of Porto Velho and in villages along the Rio Madeira, Amazon, Brazil. Int. J. Hyg. Environ. Health 216, 682–689.
José G. Dórea Faculty of Health Sciences, University of Brasília, 70919-970 Brasília, DF, Brazil E-mail address: [email protected] Available online 17 July 2015
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Letter to the editor Methylmercury in colostrum and milk of Japanese mothers
Iwai-Shimada et al. (2015)’s paper on the transfer of maternal methylmercury (MeHg) through milk lipids is a significant contribution to health and environmental sciences. This team gathered unique data related to Hg chemical species and human milk; however, a few conceptual and methodological questions need addressing. Although fish is the main MeHg carrier, the Japanese diet is also rich in rice that in China has been shown to contain MeHg (Rothenberg et al., 2013). There are few papers reporting MeHg concentrations in breast milk, especially in populations with elevated fish consumption; therefore, it is important to reference and discuss studies of high fish-consumption mothers. Iwai-Shimada et al. cited only European studies, missing a high fish-consumption study in the Amazon (Vieira et al., 2013). Vieira et al. (2013) investigated MeHg in breast milk of urban and rural mothers who, like Japanese women, consume fish as ‘‘staple foods’’. Although urban mothers showed a comparatively lower hair-Hg (1.32 lg/g) concentration, subsistence mothers had more than double the hair-Hg concentrations (8.24 lg/g) reported by Iwai-Shimada et al.’s study (3.43 lg/g). Fish consumption (reflected by hair-Hg) is an important point of comparison because the proportion of MeHg:THg in breast milk was respectively 37% and 12% for riverine and urban mothers (Vieira et al., 2013); these variations are comparable to those discussed by Iwai-Shimada et al. in Mediterranean mothers, indicating unaccounted factors associated with maternal MeHg transfer. Furthermore, in agreement with the study by IwaiShimada et al., Vieira et al. (2013) did not find a significant correlation between THg concentrations in milk and either maternal amalgam filling or daily fish consumption; nor did they find any statistically significant correlation between total hair-Hg concentration and total milk-Hg concentration or between MeHg in hair and in milk samples (Vieira et al., 2013). The unique feature of Iwai-Shimada et al.’s paper (MeHg and lipids) does not address issues central to understanding total lipids in human lactation, such as stage of lactation and type of sampling. Iwai-Shimada et al. inform us that ‘‘maternal hair and breast milk were collected two days and one month after delivery’’, yet they did not differentiate ‘colostrum’ (two-day sample) when reporting ‘breast milk’ in tables, graphs, and statistical analysis. The early post-natal mammary secretion has special physical–chemical and functional characteristics, and for that is called colostrum; this early secretion changes substantially in lipids and protein concentrations as it matures into ‘milk’ (Macias and Schweigert, 2001). Not only that, but milk fat also changes significantly between fore- and hind-milk (Dórea et al., 1982). Iwai-Shimada referenced Bjornberg et al. (2005) showing that total Hg decreases from colostrum to mature milk, but they http://dx.doi.org/10.1016/j.chemosphere.2015.06.100 0045-6535/Ó 2015 Elsevier Ltd. All rights reserved.
did not discuss this opposite trend in relation to milk lipids. Therefore, it is crucial to describe how colostrum and milk were collected and accounted for in relation to MeHg concentrations. There is need for adjustments related to the estimated ‘‘lactational exposure to MeHg in one-month-old infants’’; a ‘‘body weight of 4.0 kg’’ was assumed along with ‘‘an average daily milk consumption of 800 mL’’, which may overestimate milk intake. Grandjean et al. (1994) recommend 125 mL/kg body weight/day, which would give a daily milk intake of 600 mL. Additionally, it is not clear if the ‘lactational exposure’ MeHg represents one or two samples (colostrum or mature milk). Thus, differences in milk lipids between colostrum and mature milk, as well as daily colostrum (first 10 days) based on milk consumption rate per body weight may result in less MeHg transfer during the first month of breastfeeding. Another issue deserving attention is related to ‘‘repeated measurement’’ of the samples from the same mother taken on two occasions – two days and one month as stated in the footnotes of Tables 1 and 2 (‘‘Maternal blood and breast milk were collected one day postpartum and one month after delivery, respectively’’); what does ‘‘Breast milk’’ represent? Is it a pooled analysis of two samples? If so, how was it dealt with in the correlation and regression analysis? Because only ‘‘milk’’ sample is referred to, we are not informed if the colostrum (one- or two-day sample) was included in the one-month milk reported. References Bjornberg, K.A., Vahter, M., Berglund, B., Niklasson, B., Blennow, M., SandborghEnglund, G., 2005. Transport of methylmercury and inorganic mercury to the fetus and breast-fed infant. Environ. Health Perspect. 113, 1381–1385. Dórea, J.G., Horner, M.R., Bezerra, V.L., 1982. Correlation between changeable human milk constituents and milk intake in breast-fed babies. J. Pediatr. 101, 80–83. Grandjean, P., Jorgensen, P.J., Weihe, P., 1994. Human milk as a source of methylmercury exposure in infants. Environ. Health Perspect. 102, 74–77. Iwai-Shimada, M., Satoh, H., Nakai, K., Tatsuta, N., Murata, K., Akagi, H., 2015. Methylmercury in the breast milk of Japanese mothers and lactational exposure of their infants. Chemosphere 126, 67–72. Macias, C., Schweigert, F.J., 2001. Changes in the concentration of carotenoids, vitamin A, alpha-tocopherol and total lipids in human milk throughout early lactation. Ann. Nutr. Metab. 45, 82–85. Rothenberg, S.E., Yu, X., Zhang, Y., 2013. Prenatal methylmercury exposure through maternal rice ingestion: insights from a feasibility pilot in Guizhou Province, China. Environ. Pollut. 180, e291e–e298e. Vieira, S.M., de Almeida, R., Holanda, I.B., Mussy, M.H., Galvão, R.C., Crispim, P.T., Dórea, J.G., Bastos, W.R., 2013. Total and methyl-mercury in hair and milk of mothers living in the city of Porto Velho and in villages along the Rio Madeira, Amazon, Brazil. Int. J. Hyg. Environ. Health 216, 682–689.
José G. Dórea Faculty of Health Sciences, University of Brasília, 70919-970 Brasília, DF, Brazil E-mail address: [email protected] Available online 17 July 2015