Early exposure to natural elements that are toxic – cadmium, mercury, and lead – can have long-term adverse health consequences. Children exposed to these elements while still in the uterus and while breast-feeding may suffer lasting damage to the brain and nervous system and to the kidneys and liver. The question is: to what extent can selenium supplementation reduce the risk of toxic damage?
Given the dangerous nature of these poisonous heavy metals – cadmium, mercury, and lead – both for the mother and for the fetus and the neonate, it is difficult to carry out randomized controlled studies. Instead, the best evidence we have for the beneficial effects of selenium supplementation comes from studies that relate the degree of exposure and the selenium status of the mother and the child.
Does higher selenium status reduce the risk of toxic poisoning by cadmium, mercury, and lead? I review some of the available studies.
Placental transfer of heavy metals
Dr. Chen and a team of researchers examined the data from samples of mothers’ blood, umbilical cord blood, and postnatal blood from participants in the Boston Birth Cohort. The researchers reported the following findings:
- The Boston Birth Cohort mothers’ exposure to these toxic elements – cadmium, mercury, and lead – was more extensive than imagined.
- There was a high degree of transfer of these poisonous elements from the mothers to the fetuses.
- There was a significantly higher level of mercury in maternal and cord plasma and red blood cells of the mothers who gave birth to preterm or low birth weight babies as compared with the mercury levels in the mothers who carried their babies to term and whose babies had normal birth weights [Chen].
These results indicate a need for pre-screening of women who are planning a pregnancy for higher concentrations of cadmium, mercury, and lead. Then, depending on the results of the screening, an intervention with a high-selenium yeast preparation may well be indicated.
Cadmium and selenium and birth characteristics
Dr. Al-Saleh and a team of researchers measured the cadmium and selenium levels in the umbilical-cord blood and in the placentas of 250 healthy mothers. Their results showed a negative association between in utero exposure to cadmium and the birth characteristics of the fetuses.
- Higher levels of cadmium in the umbilical cord were negatively associated with the following indicators of birth health:
- five-minute Apgar scores
- birth height
- birth weight
- placental thickness
- Higher levels of cadmium in the mothers’ blood samples were associated with an increased risk of low-weight babies (babies that were small for their gestational ages).
- Higher placental cadmium levels were associated with lower placenta weight.
Note: The Apgar score is the result of a quick assessment of the baby’s health at birth and at five minutes following birth. It assesses the baby’s Appearance, Pulse, Grimace, Activity, and Respiration.
In the Al-Saleh study, higher umbilical cord selenium levels were associated with higher placenta weight and greater placental thickness.
The researchers concluded that the mechanisms by which selenium can reduce the extent of the negative effects of cadmium poisoning on newborn babies are not yet known. They suggested that the beneficial effect of selenium supplementation may depend not just on the increase in selenium status but also on the forms of the selenium used in the supplementation.
They called for further speciation of selenium in studies of the effect of cadmium, mercury, and lead poisoning [Al-Saleh]. Which forms of selenium are likely to be most effective against heavy metal intoxication? That is what we need to know with greater certainty. At present, it seems that high-selenium yeast preparations are most effective.
Cadmium and selenium and kidney function
Dr. Skröder and a team of researchers investigated the kidney function of children aged 4.5 years. The children had been exposed to various levels of cadmium and arsenic and selenium in their food and drinking water.
The team’s findings indicated a relationship among cadmium exposure, and selenium status, and kidney function:
- The extent of the children’s exposure to cadmium was seen to have had an adverse effect on kidney function.
- Better selenium status was seen to have a protective effect against the harmful effects of cadmium exposure [Skröder].
Cadmium and selenium and birth weights
Dr. Sun and a team of researchers investigated selenium status and the extent of exposure to cadmium and lead in mothers and fetuses. Their investigations led to the following findings:
- The mothers’ blood cadmium, lead, and selenium status was reflected in the cadmium, lead, and selenium status in the umbilical cord.
- The extent of exposure to cadmium was seen to affect the newborn children’s birth weight.
- Higher selenium intakes seemed to reduce the umbilical cord blood cadmium concentration.
- Higher selenium intakes seemed to promote fetal growth [Sun].
Selenium and mercury and amalgam-based dental treatment
Dr. Razagui and a team of researchers measured the mercury and selenium concentrations in the scalp hair samples of new mothers and their neonates.
- The data from their study showed that amalgam-based dental treatment during pregnancy is associated with higher prenatal exposure to mercury.
- The association between mothers’ higher mercury concentrations and neonates’ higher mercury concentrations was especially strong in cases of the mothers who had had amalgam fillings removed and/or replaced during pregnancy.
- Better selenium status alleviated the risk of harmful effects from high mercury exposure [Razagui].
Smoking and selenium and cadmium levels
Dr. Kosanovic and a team of researchers investigated the extent of cadmium and selenium status in mothers and fetuses during the pregnancies of women with normal blood pressure and with high blood pressure.
- Pregnant women who smoked had significantly higher cadmium and significantly lower selenium concentrations in blood than was the case for nonsmokers.
- The selenium concentrations in the umbilical cord blood of smokers, as compared with nonsmokers, were also significantly lower, meaning that the fetus was getting less protective selenium.
- Selenium concentrations in the amniotic fluid of smokers were also significantly lower than in the amniotic fluid of nonsmokers.
- The study data show that high blood pressure in pregnant women smokers is significantly associated with higher blood cadmium concentrations [Kosanovic].
Planning a pregnancy?
The above studies indicate that women planning a pregnancy need to have their blood tested for the levels of harmful heavy metals and to have their blood tested for the levels of protective selenium.
Adequate supplies of selenium before and during pregnancy can protect not only against the worst effects of heavy metal intoxication but also against the risk of pre-eclampsia, a serious disorder in pregnancy.
Al-Saleh, I., Al-Rouqi, R., Obsum, C. A., Shinwari, N., Mashhour, A., Billedo, G., & Rabbah, A. (2015). Interaction between cadmium (Cd), selenium (Se) and oxidative stress biomarkers in healthy mothers and its impact on birth anthropometric measures. International Journal Of Hygiene And Environmental Health, 218(1), 66-90.
Chen, Z., Myers, R., Wei, T., Bind, E., Kassim, P., Wang, G., & Wang, X. (2014). Placental transfer and concentrations of cadmium, mercury, lead, and selenium in mothers, newborns, and young children. Journal Of Exposure Science & Environmental Epidemiology, 24(5), 537-544.
Kosanovic, M., Jokanovic, M., Jevremovic, M., Dobric, S., & Bokonjic, D. (2002). Maternal and fetal cadmium and selenium status in normotensive and hypertensive pregnancy. Biological Trace Element Research, 89(2), 97-103.
Razagui, I. B., & Haswell, S. J. (2001). Mercury and selenium concentrations in maternal and neonatal scalp hair: relationship to amalgam-based dental treatment received during pregnancy. Biological Trace Element Research, 81(1), 1-19.
Skröder, H., Hawkesworth, S., Kippler, M., El Arifeen, S., Wagatsuma, Y., Moore, S. E., & Vahter, M. (2015). Kidney function and blood pressure in preschool-aged children exposed to cadmium and arsenic–potential alleviation by selenium. Environmental Research, 140,205-213.
Sun, H., Chen, W., Wang, D., Jin, Y., Chen, X., & Xu, Y. (2014). The effects of prenatal exposure to low-level cadmium, lead and selenium on birth outcomes. Chemosphere, 10,833-39.
Disclaimer: The information presented in this review article is not intended as medical advice and should not be construed as such.