This page contains a Flash digital edition of a book.
Opinion Infection and intelligence


Prof Shima Gyoh thinks evidence of the correlation between infection and intelligence should inform governments of the absolute priority to raise citizenry out of poverty


Are infectious diseases sapping people’s brainpower in the world’s poorest countries? A well-researched work by Christopher Eppig et al1


suggests this is so. They


adduce evidence that repeated heavy infection and infestation afflicting growing children constitutes a most powerful factor in compromising their intelligence. Facts about the human brain sound like fiction.


Weighing 1.4kg on average, it contains about 100bil- lion neurons. Their important companion cells, called neuroglia, outnumber the neurons ten to one. Each neuron makes thousands of connections with the others through tiny innumerable junctions called synapses. Our brains form around a million new connections every second of our lives and utilise 20% of the energy consumed by the adult body at rest.


It is calculated that the neurons multiply at the rate


of 250000 per minute in early pregnancy. With regard to size, the human baby is nearly all brain at birth; the body takes years to catch up. After birth, the skull remains open first through membranes and later cartilage where its various plates meet to allow for further rapid expan- sion of the brain, especially in the first 3 years. It is logi- cal to assume that shortage of protein and other nutri- ents so common in developing countries, especially at the time of weaning, would somehow adversely affect the development of the brain and perhaps result in lower intelligence as suggested by Eppig and his co-workers. The studies of Holliday in 19862


showed that, at


birth, about 87% of the energy a baby uses goes to power the development of the brain alone. This propor- tion gradually drops as the body catches up, but at the age of 5, it is still at the high level of 44%. However, in the first 5 years in developing countries, the infant is bombarded by all sorts of life-threatening infections, infestations, and diarrhoeal diseases, and many do not survive. These require a lot of energy to fight, and the body diverts a huge proportion of available energy to combat the onslaught. The welcome by-product is the the fact that the body acquires the ability to handle a wide spectrum of antigens, decreasing the episodes of abnormal reaction to environmental and endogenous antigenic challenge, such as asthma and auto-allergic diseases.3


The cost, however, may be enormous, as the


brain may have to cope with less energy than ideal for optimum development at such sensitive times. Does this result in an overall reduction of cognitive ability? Intelligence may be impossible to measure in absolute


Prof Shima Gyoh has held many posts ranging from village doctor to DG of Nigeria’s Federal Ministry of Health and Chair of the Medical and Dental Council of Nigeria.


July 2012


terms applicable to all cultures, but for each society comparative methods (e.g. WAM, LVE, LVCD, AVED) have been designed to measure the IQ (intelligence quotient) and the results give a reasonable yardstick for comparing human cognitive abilities in particular environments. This subject tends to be sensitive, as it has been misused to justify oppression at various times in human history. However, it is too important to ignore, and the conclusions reached by Eppig and his colleagues have enormous implications for developing countries. Taking the average intelligence from the 2006 work they directly measured the IQ in 113 na-


of Vanhamen,4


tions using the LVE and the WEAM methods, estimated it for 79 countries and then did sample measurements in the estimated countries for validation. They plotted the national average IQ against infectious disease burden calculated from DALY (disability adjusted life years) lost using World Health Organization records. Among the numerous conditions suspected to affect human cognitive ability, the ones used in this study were: education, protein–energy malnutrition, income per capita, average high winter temperatures (as cold environments are said to be more challenging to life), distance from Central Africa (on the assumption that the more intelligent members of a tribe were more likely to wander further from the starting point of human migration). Correlation with infectious diseases was very strong, and was in fact the underlying cause of associa- tion in practically all the other factors. This is supported by the Flynn effect which describes the large increases in IQ that occur within a few generations as an epigen- etic effect of economic development. Most of us that live in this region might have as- signed the frequently observed difficulties of mental grasp afflicting the less fortunate members of our society to lack of education, but elimination of the influence of infection surprisingly makes education alone insig- nificant. Raising the standard of living of the average citizen within the shortest time possible should be the unchallenged priority in the developing world, particu- larly in Africa where our governments should worry that a slow pace of emergence from poverty, ignorance, and the infective stage of national development might compound our countries’ challenges in the most painful way – lowering of the average national intelligence.


References 1. Eppig C, Fincher CL, Thornhill R. Parasite prevalence and the worldwide distri- bution of cognitive ability. Proc R Soc B 2010; 277: 3801–8.


2.


3. 4.


Falkner F, Tanner JM, Holliday MA. 1986: Body composition and energy needs during growth. In Human growth: a comprehensive treatise, Vol. 2. Eds Falkner F, Tanner JM. New York: Plenum; pp. 101–17.


Gyoh S. Killing bacteria for a sterile environment. Afr Health 2012; 34: 5.


Lynn R, Vanhamen T. National IQ and economic development: a study of eighty- one nations. Mankind Quart 2001; 41: 415–35.


Africa Health 5


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68