Effects of maternal fish consumption on children’s cognitive health
Leino, O. 1*, Karjalainen, A.2 and Tuomisto, J.T.1
1* National Institute for Health and Welfare, Department of Environmental Health, P.O. Box 95, FI-70701 Kuopio, Finland. [email protected]
2 University of Jyväskylä, Department of Biological and Environmental Science and Finnish Environment Institute, Jyväskylä Unit, P.O. Box 35, FI-40014 University of Jyväskylä, Finland.
BACKGROUND
Figure 1. Fish consumption of pregnant women (n=3837) in Finland.
Mean and 90% confidence interval.
25
Fish consumption g/day
There are number of studies showing adverse effect of methylmercury (MeHg) on brains that
decrease intelligence quotient (IQ). Several national agencies have recommended reduced fish
consumption for pregnant women and for women in childbearing age in order to avoid adverse
prenatal and postnatal health effects due to MeHg exposure. However, the beneficial effects of
omega-3 fatty acids in fish (more specifically, DHA docosahexaenoic acid) on the brain are also
recognized. Therefore, relationship of fish consumption and the net IQ effects is an interesting
question. Additionally, these two effects share the common metric (IQ change) which simplifies the
question and provides us a less ambiguous result.
20
15
5
IQ is a composite index that averages a child’s performance across many functional domains,
providing an overall picture of cognitive health. Prenatal period is much more sensitive to the toxic
effects of MeHg than adulthood. Similarly, the positive health effects of omega-3 fatty acids relate
to infants.
Some specifications of the model:
Graph 1. A simplified diagram of the model
DHA
concentration
in fish
MeHg
concentration
in fish
Maternal fish
consumption
0
Baltic herring
(Clupea
harengus
membras)
Herring
(Clupea
harengus)
Vendace
(Coregonus
albula)
Maternal
MeHg intake
1.00E-04
DHA
exposureresponse
function on
IQ
A screenshot from the
Analytica™ MonteCarlo programming
software
Maternal
MeHg
exposure
Maternal
DHA
benefits
Maternal
MeHg
risks
MeHg
exposureresponse
function on
IQ
Maternal Net
health effects
on IQ
Lean fish
7.00E-05
Fatty fish
6.00E-05
3.00E-05
2.00E-05
Twice a
month
3) Only fatty fish consumption scenario.
The latter two scenarios are hypothetical as we wanted to study the most extreme effects of different
fish consumption patterns on child’s IQ. We used established exposure-response relationships for
benefits (Cohen et al 2005b) and risks (Axelrad 2007 and Cohen 2005a).
Three times Four times Five times a Six times a
a month
a month
month
month
Seven
times a
month
Highest consumption
frequency in lean fish
consumption scenario
approaches the reference
dose level
Lean fish
800
Fatty fish
700
Pregnant women
Recommended DHA intake
level is achieved on the
high consumption
frequencies
600
500
400
300
Recommended daily DHA intake
Eating lean fish does not
provide enough DHA.
200
100
0
Once a
month
Twice a
month
Three times Four times Five times a Six times a
a month
a month
month
month
Seven
times a
month
Fish consumption frequency
Figure 4. Net IQ effect on children, presented with consumption in hypothetical
fish consumption frequencies, and with three fish consumption scenarios
1
IQ effects are quite
modest on all consumption
frequencies and
consumption scenarios.
However, in fatty fish
scenario the net effect is
positive, whereas in lean
fish it is negative
90% uncertainty intervalls
are wide, suggesting
potentially greater effects
0.5
Net health effect (IQ points)
2) Only lean fish consumption scenario
In Finland 70% of MeHg is
attributable to fish
consumption
Pregnant women
4.00E-05
900
DATA
1) Fish consumption based on a food frequency questionnaire data from year 2007
Tuna
(Thunnus
thynnus)
Fish fat percent 3.0%
divides fish to lean and
fatty subgroups in this
study
5.00E-05
■ Linear exposure-response
relationships
We conducted a quantitative benefit-risk assessment of DHA and MeHg on the total IQ effects of
prenatal fish consumption to children using Monte-Carlo simulation. We also constructed three fish
consumption scenarios by Finnish pregnant women with seven consumption frequencies:
Atlantic
salmon (Salmo
salar)
Figure 3. DHA benefits on IQ at seven hypothetical consumption frequencies,
and with three fish consumption scenarios. Mean and 90% CI
■ Two exposure-response functions for
MeHg with equal weigh.
■ No other sources of exposure than
fish consumption taken into account
Saithe
(Pollachius
virens)
Fish consumption frequency
Daily DHA intake
Maternal
DHA
exposure
Perch (Perca
f luviatilis)
U.S.EPA Reference dose
8.00E-05
0.00E+00
Once a
month
■ Latin Hypercube sampling
■ Log normal distributed pollutant
concentration and fish consumption
distributions
Shrimp
(Pandalus)
1.00E-05
■ single-compartment model in the
MeHg calculations
Bodyweight
Rainbow trout
(Onchorchys
mykiss)
9.00E-05
■ 20000 iterations
Assumptions in the model:
Pike (Esox
lucius)
Figure 2. MeHg exposure on seven hypothetical consumption frequencies, and
with three fish consumption scenarios
■ ≈ 50 variables
Maternal
DHA intake
Whitefish
(Coregonus
lavaretus)
Fish species
MeHg exposure (m g/kg bw)
EXPOSURE TO MeHg
Humans are primarily exposed to MeHg through their diet, in Finland via fish consumption.
Maternal hair mercury concentrations as low as 10-20 µg/g during pregnancy are associated with the
lowest level (5%) risks of first MeHg -caused symptoms to the children (MeHg episode in Iraq).
Fortunately, in Finland population hair mercury concentrations are typically under 1 µg/g, but the
safety of high fish consumers and children are open questions.
Total fish
consumption
= 36.62
g/day =
13.36 kg/a
10
0
-0.5
Lean fish
Fatty fish
-1
Pregnant women
-1.5
Once a
month
Twice a
month
Three times Four times Five times a Six times a Seven times
a month
a month
month
month
a month
Consumption frequency
ACKNOWLEDGEMENTS
RESULTS AND CONCLUSIONS
According to our data, pregnant women are consuming fish approximately once a week (mean 1.13,
90% CI 0.18-3.29, Fig 1). This information is an interesting intermediate result as the current
recommended fish consumption in Finland is twice a week with varying fish species intake. The
recommended daily DHA intake is just about achieved only by pregnant women consuming fatty fish
seven times a week.
In 1995 U.S. Environmental Pollution Agency (EPA) derived a reference dose (RfD) of 1 x 104 mg
per kilogram of bodyweight for MeHg. According to our model, MeHg exposures of the general
population and pregnant women in Finland typically are 3-6 x 105 mg per kilogram of bodyweight.
The net health effects are close to zero, fatty fish consumption having a small beneficial effect and
lean fish consumption bearing a minor adverse effect. We concluded that the low level exposure to
mercury in fish with the current Finnish (North European) fish consumption pattern does not pose a
risk to children’s cognitive development. Eventually, individual’s social skills will rather dictate
his/her success later in life.
The work has been a part of the BENERIS project funded by the EU (Contract
No. Food-CT-2006-022936). We would like to thank Mrs. Aune Vihervuori at
the RKTL for a kind co-operation, and Dr. Tero Hirvonen (EVIRA) for
providing pregnant women consumption data for the model.
REFERENCES
Leino, O., Karjalainen, A., and Tuomisto JT. 2009 Omega-3 fatty acid and methylmercury effects on
intelligence quotient (IQ) in children due to prenatal fish consumption in Finland. Manuscript.
Leino, O., Tainio, M., and Tuomisto, JT. 2008. Comparative risk analysis of dioxins in fish and fine particles
from heavy-duty vehicles. Risk Analysis, Vol 28, No. 1.
Cohen J.T., PhD, Bellinger D.C., PhD, and Shaywitz, B.A. 2005a. A Quantitative Analysis of Prenatal Methyl
Mercury Exposure and Cognitive Development. Am J Prev Med 2005;29(4)
Cohen, J.T., PhD, Bellinger, D.C, PhD, W.E., MD, Bennett A., and Shaywitz B.A. 2005b. A Quantitative
Analysis of Prenatal Intake of n-3 Polyunsaturated Fatty Acids and Cognitive Development. American Journal
of Preventive Medicine 2005;29(4):366–374).
Axelrad, D.A., Bellinger, D.C., Ryan, L.M., and Woodruff, T.J. Dose–Response Relationship of Prenatal
Mercury Exposure and IQ: An Integrative Analysis of Epidemiologic Data. Environmental Health
Perspectives. Vol 115, Number 4, 2007.
U.S.EPA IRIS database http://cfpub.epa.gov/ncea/iris/index.cfm