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Prenatal Mercury Exposure Cancels Out Cognitive Benefits of Exercise


Mercury comes from industrial pollution in the air that falls into the water, where it turns into methylmercury and accumulates in fish. The main exposure of humans to methylmercury is through the consumption of marine fish. Once taken up from food it can be transported by the blood stream, cross the blood-brain-barrier and reach the central nervous system, severely affecting neural development in fetuses.

The new study:
This is one of the first studies to examine how methylmercury exposure in the womb may affect cognitive function in adults. The scientists, based at the Harvard T.H. Chan School ofPublic Health, suspect that prenatal exposure to methylmercury may limit the ability of nervous system tissues to grow and develop in response to increased aerobic fitness.

“We know that neurodevelopment is a delicate process that is especially sensitive to methylmercury and other environmental toxins, but we are still discovering the lifelong ripple effects of these exposures,” said Gwen Collman, Ph.D., director of the NIEHS Division of Extramural Research and Training. “This research points to adult cognitive function as a new area of concern.”.

The 197 study participants are from the Faroe Islands, 200 miles north of England,  where map showing the position of the Faroe islands between the Norwegian Sea and the North Atlantic Oceanfish is a major component of the diet. Their health has been followed since they were in the womb in the late 1980s. At age 22, this subset of the original 1,022 participants took part in a follow-up exam that included estimating the participants’ VO2 max, or the rate at which they can use oxygen, which increases with aerobic fitness.

Figure: position of the Faroe islands between the Norwegian Sea and the North Atlantic Ocean

Also, a range of cognitive tests were performed related to short-term memory, verbal comprehension and knowledge, psychomotor speed, visual processing, long-term storage and retrieval, and cognitive processing speed.

Overall, the researchers found that higher VO2 max values were associated with better neurocognitive function, as expected based on prior research. Cognitive efficiency, which included cognitive processing speed and short term memory, benefitted the most from increased VO2 max.

But when the researchers divided the participants into two groups based on the methylmercury levels in their mothers while they were pregnant, they found that these benefits were confined to the group with the lowest exposure. Participants with prenatal methylmercury levels in the bottom 67 percent, or levels of less than 35 micrograms per liter in umbilical cord blood, still demonstrated better cognitive efficiency with higher VO2 max. However, for participants with higher methylmercury levels, cognitive function did not improve as VO2 max increased.

“We know that aerobic exercise is an important part of a healthy lifestyle, but these findings suggest that early-life exposure to pollutants may reduce the potential benefits,” added Collman. “We need to pay special attention to the environment we create for pregnant moms and babies.”

The U.S. Food and Drug Administration recommends that children and women of childbearing age eat two to three weekly servings of fish low in mercury as part of a healthy diet. Low mercury fish include salmon, shrimp, pollock, canned light tuna, tilapia, catfish, and cod. Four types of fish should be avoided because of typically high mercury levels — tilefish from the Gulf of Mexico, shark, swordfish, and king mackerel.

The findings were published Sept. 9 in the journal Environmental Health Perspectives. In addition to NIH funding, the research was supported by the Danish Council for Strategic Research, Programme Commission on Health, Food, and Welfare.

Source: The above post is reprinted from materials provided by NIH/National Institute of Environmental Health Sciences. Note: Content was edited for style and length

The original study:

Philippe Grandjean, Pal Weihe, Sonja Vestergaard, Frodi Debes, Youssef Oulhote. Aerobic Fitness and Neurocognitive Function Scores in Young Faroese Adults and Potential Modification by Prenatal Methylmercury Exposure. Environ. Health Perspec., 2016; DOI: 10.1289/ehp274

Related studies (newest first):

F. Debes, P. Weihe, P. Grandjean, Cognitive deficits at age 22 years associated with prenatal exposure to methylmercury. Cortex, 74 (2015) 358-369. doi: 10.1016/j.cortex.2015.05.017

P. Grandjean, P.J. Landrigan, Neurobehavioural effects of developmental toxicity. Lancet Neurol., 13 (2014) 330-338. doi: 10.1016/s1474-4422(13)70278-3

P. Grandjean, P. Weihe, F. Debes, A.L. Choi, E. Budtz-Jorgensen, Neurotoxicity from prenatal and postnatal exposure to methylmercury. Neurotox. Teratol., 43 (2014) 39-44. doi: 10.1016/j.ntt.2014.03.004

Katie Sokolowski, Maryann Obiorah, Kelsey Robinson, Elizabeth McCandlish, Brian Buckley, Emanuel DiCicco-Bloom, Neural Stem Cell Apoptosis after Low-Methylmercury Exposures in Postnatal Hippocampus Produce Persistent Cell Loss and Adolescent Memory Deficits, Dev. Neurobiol., 73/12 (2013) 936-949. doi: 10.1002/dneu.22119

M.R. Karagas, A.L. Choi, E. Oken, M. Horvat, R. Schoeny, E. Kamai, W. Cowell, P. Grandjean, S. Koorick, Evidence on the human health effects of low-level methylmercury exposure. Environ Health Perspect 120 (2012) 799-806. doi: 10.1289/ehp.1104494

Anthony Falluel-Morel, Katie Sokolowski, Helene M. Sisti, Xiaofeng Zhou, Tracey J. Shors, Emanuel DiCicco-Bloom, Developmental mercury exposure elicits acute hippocampal cell death, reductions in neurogenesis, and severe learning deficits during puberty, J. Neurochem., 103/5 (2007) 1968–1981. doi:  10.1111/j.1471-4159.2007.04882.x

E. Budtz-Jørgensen, P. Grandjean, P. Weihe, Separation of risks and benefits of seafood intake. Environ. Health Perspect., 115 (2007) 323-327. doi: 10.1289/ehp.9738

F. Debes, E. Budtz-Jorgensen, P. Weihe, R.F. White, P. Grandjean, Impact of prenatal methylmercury exposure on neurobehavioral function at age 14 years. Neurotoxicol. Teratol., 28 (2006) 363-375. doi: 10.1016/j.ntt.2006.02.004

P. Grandjean, P. Weihe, P.J. Jorgensen, T. Clarkson, E. Cernichiari, T. Videro, Impact of maternal seafood diet on fetal exposure to mercury, selenium, and lead. Arch. Environ. Health, 47 (1992) 185-195. doi: 10.1080/00039896.1992.9938348

P. Oudar, L. Caillard, G. Fillion. In Vitro Effect of Organic and Inorganic Mercury on the Serotonergic System, Basic Clin. Pharmacol. Toxicol., 65/4 (1989) 245-248. doi: 10.1111/j.1600-0773.1989.tb01166.x

Related EVISA Resources

Brief summary: Chemical speciation analysis for nutrition and food science
Brief summary: Speciation and Toxicity
Link database: Toxicity of Organic mercury compounds
Link database: Human exposure to methylmercury via the diet

Related EVISA News

August 3, 2016: New study identifies source of methylmercury in Southern Ocean sea ice
September 2, 2014: Man is significantly contaminating oceans with mercury
September 14, 2013: Toxic Methylmercury-Producing Microbes More Widespread Than Realized
August 6, 2013: Bacterial methylation of mercury not only starting from oxidized mercury
February 8, 2013: ORNL scientists solve mystery about mercury methylation
June 17, 2012: Factors Affecting Methylmercury Accumulation in the Food Chain

last time modified: September 17, 2016


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