Nutrition and Behaviour
27th February 2017
Lecture 7: Micro-nutrient Status and Behaviour
The Flynn Effect, Flynn (1984):
,The Flynn effect is the substantial and long-sustained increase in intelligence test scores measured in many parts of
the world from roughly 1930 to the present day. When intelligence quotient (IQ) tests are initially standardized using
a sample of test-takers, by convention the average of the test results is set to 100 and their standard deviation is set
to 15 or 16 IQ points. When IQ tests are revised, they are again standardized using a new sample of test-takers,
usually born more recently than the first. Again, the average result is set to 100. However, when the new test
subjects take the older tests, in almost every case their average scores are significantly above 100.
Political scientist who collected data and found a general tendency for people’s ability to perform on intelligence
tests to increase across the years.
Multiple possible explanations such as people staying in education for longer, more affluent, increased use of
television so verbal stimulation, educated to a higher level.
If the above mechanisms were true then there would not be the pattern of improved performance in all countries,
with different cultures. However, there is an improved performance (see above graphs of different countries).
Raven (2000): For the Raven’s Progressive Matrices test, subjects born over a 100-year period were compared in Des
Moines, United States, and separately in Dumfries, Scotland. Improvements were remarkably consistent across the
whole period, in both countries.
Trahan et al. (2014): Found that the effect was about 2.93 points per decade, based on both the Stanford-Binet and
Wechsler tests; they also found no evidence the effect was diminishing.
Ronnlund and Nilsson (2009): Thought the effect is most associated with IQ increases, a similar effect has been
found with increases in attention and of semantic and episodic memory.
Also these mechanisms would suggest improvements specific to verbal intelligence. However, there are much
greater gains in non-verbal intelligence.
This began the thinking about how this may not be a total social phenomenon as if it was, you would expect to see
greater gains in verbal intelligence.
, Lynn (1990): The role of nutrition in secular increases in intelligence.
Height increased by 1 SD over the last 50 years.
Head circumference correlates with the size of the brain:
Miller and Corsellis (1977): Brain weight has increased by 6g/decade.
Ounsted et al. (1985): Head circumference has increased by 1 SD in 50 years.
Lynn argued the case that it reflects, in part at least, a biological change likely the result of changes in nutrition.
Nutrition has an influence on IQ, height and head size.
Lynn (1989): Height, head circumference and IQ correlate.
Churchill (1965):
MZ twins have identical genetics and are likely to be treated similarly by parents but what about birth weight?
Found that MZ twins differed on average of 260g at birth.
Intelligence measured between 5 and 15 years and found:
IQ of heavier twin was 85.2
IQ of lighter twin was 80.9
Suggests as the one twin was heavier, it was likely that they received more of the nutrients available. Shows
potential association between nutrients and IQ.
Willerman and Churchill (1967):
Verbal IQ was 0.4 (basically no difference) greater in the heavier MZ twin
Performance IQ was 5.3 greater in heavier twin.
So there was a difference between the nutrition obtained and intelligence but specifically only with Performance IQ.
This can then be seen to be maintained later in life too...
Hendrichsen et al. (1986):
At 13 years of age:
Verbal IQ had no difference between the MZ twins
Performance IQ was 7.1 greater in heavier twin.
Edmonds et al. (2010):
Examined whether suboptimal intrauterine growth relates to impaired cognitive outcome by comparing birth weight
and cognition in monozygotic twins and considered whether children within-pair differences in birth weight were
related to within-pair differences in IQ scores.
71 MZ twin pairs
Verbal IQ but not Performance IQ score was affected by prenatal growth restriction.
27th February 2017
Lecture 7: Micro-nutrient Status and Behaviour
The Flynn Effect, Flynn (1984):
,The Flynn effect is the substantial and long-sustained increase in intelligence test scores measured in many parts of
the world from roughly 1930 to the present day. When intelligence quotient (IQ) tests are initially standardized using
a sample of test-takers, by convention the average of the test results is set to 100 and their standard deviation is set
to 15 or 16 IQ points. When IQ tests are revised, they are again standardized using a new sample of test-takers,
usually born more recently than the first. Again, the average result is set to 100. However, when the new test
subjects take the older tests, in almost every case their average scores are significantly above 100.
Political scientist who collected data and found a general tendency for people’s ability to perform on intelligence
tests to increase across the years.
Multiple possible explanations such as people staying in education for longer, more affluent, increased use of
television so verbal stimulation, educated to a higher level.
If the above mechanisms were true then there would not be the pattern of improved performance in all countries,
with different cultures. However, there is an improved performance (see above graphs of different countries).
Raven (2000): For the Raven’s Progressive Matrices test, subjects born over a 100-year period were compared in Des
Moines, United States, and separately in Dumfries, Scotland. Improvements were remarkably consistent across the
whole period, in both countries.
Trahan et al. (2014): Found that the effect was about 2.93 points per decade, based on both the Stanford-Binet and
Wechsler tests; they also found no evidence the effect was diminishing.
Ronnlund and Nilsson (2009): Thought the effect is most associated with IQ increases, a similar effect has been
found with increases in attention and of semantic and episodic memory.
Also these mechanisms would suggest improvements specific to verbal intelligence. However, there are much
greater gains in non-verbal intelligence.
This began the thinking about how this may not be a total social phenomenon as if it was, you would expect to see
greater gains in verbal intelligence.
, Lynn (1990): The role of nutrition in secular increases in intelligence.
Height increased by 1 SD over the last 50 years.
Head circumference correlates with the size of the brain:
Miller and Corsellis (1977): Brain weight has increased by 6g/decade.
Ounsted et al. (1985): Head circumference has increased by 1 SD in 50 years.
Lynn argued the case that it reflects, in part at least, a biological change likely the result of changes in nutrition.
Nutrition has an influence on IQ, height and head size.
Lynn (1989): Height, head circumference and IQ correlate.
Churchill (1965):
MZ twins have identical genetics and are likely to be treated similarly by parents but what about birth weight?
Found that MZ twins differed on average of 260g at birth.
Intelligence measured between 5 and 15 years and found:
IQ of heavier twin was 85.2
IQ of lighter twin was 80.9
Suggests as the one twin was heavier, it was likely that they received more of the nutrients available. Shows
potential association between nutrients and IQ.
Willerman and Churchill (1967):
Verbal IQ was 0.4 (basically no difference) greater in the heavier MZ twin
Performance IQ was 5.3 greater in heavier twin.
So there was a difference between the nutrition obtained and intelligence but specifically only with Performance IQ.
This can then be seen to be maintained later in life too...
Hendrichsen et al. (1986):
At 13 years of age:
Verbal IQ had no difference between the MZ twins
Performance IQ was 7.1 greater in heavier twin.
Edmonds et al. (2010):
Examined whether suboptimal intrauterine growth relates to impaired cognitive outcome by comparing birth weight
and cognition in monozygotic twins and considered whether children within-pair differences in birth weight were
related to within-pair differences in IQ scores.
71 MZ twin pairs
Verbal IQ but not Performance IQ score was affected by prenatal growth restriction.
