Cognitive function improves with aerobic exercise, but not for people exposed to high levels of mercury before birth, according to research funded by the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health (NIH). Adults with high prenatal exposure to methylmercury, which mainly comes from maternal consumption of fish with high mercury levels, did not experience the faster cognitive processing and better short term memory benefits of exercise that were seen in those with low prenatal methylmercury exposures.
Background:
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 of Public 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
fish 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 litre 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 mums
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.
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
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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 24, 2024
