INFECTIOUS disease is taking an unexpected toll by sapping people鈥檚 brainpower in the world鈥檚 poorest countries. So say Christopher Eppig and colleagues at the University of New Mexico, Albuquerque, who found that a country鈥檚 disease burden is strongly linked to the average IQ of its population.
Building and maintaining the brain requires 87 per cent of all the body鈥檚 energy in newborns and 44 per cent in 5-year-old children. Fighting infection also takes enormous amounts of energy, so children may struggle to do both at the same time.
Eppig reasoned that an increased risk of catching an infectious disease during critical developmental stages may affect subsequent IQ levels. His team matched three sets of IQ estimates of healthy people in 192 countries, against the World Health Organization鈥檚 estimate of the burden of 28 infectious diseases in those countries. With only a few exceptions, they found very high correlations: the more disease, the lower the IQ.
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Disease was more closely related to IQ than any other variable they tested. IQ differences are known to correlate with GDP, and educational and nutritional levels, but when variation in IQ due to disease was accounted for, IQ showed no correlation with these other factors (, DOI: 10.1098/rspb.2010.0973).
This may explain the effect discovered by the political philosopher James Flynn, who noted that IQ soars following economic development. 鈥淥thers have suggested that it is caused by better education, but we found that infectious disease is a much better predictor,鈥� Eppig says.
Pat Pridmore of the University of Sussex, UK, says that childhood malnutrition and diseases have previously been linked to lower IQ. Eppig says that this may be because richer, better-educated and well-nourished people are less likely to get sick.
