Why have our IQ levels rocketed in recent years? The answer may lie in nutrition, Roger Dobson discovers

Take a 50-year-old IQ test and it's likely that you will emerge a genius. In fact, most of the population would almost certainly be classed as super-intelligent if they were scored on tests originally set half a century ago.

Take a 50-year-old IQ test and it's likely that you will emerge a genius. In fact, most of the population would almost certainly be classed as super-intelligent if they were scored on tests originally set half a century ago.

"If people taking an IQ test today were scored with the norms of their grandparents' performances 50 years ago, more than 90 per cent of them would be classified as geniuses, while, if our grandparents were scored today, most of them would be classed as borderline mentally retarded," says Dr Stephen Ceci, who is professor of developmental psychology at Cornell University.

The reason is that average IQ has increased around 20 points with every generation over the last 60 or so years, an increase that has been seen in more than a dozen countries, including the United Kingdom, United States, Japan, Africa, Australia and New Zealand.

Just why is unclear. Genetic factors, better-educated parents, more sophisticated toys, television and computers have all been given the credit, but with little supporting evidence.

Now, new research has given a considerable boost to the idea that nutrition and diet are largely responsible for the huge rise in IQ. It is suggested that the right nutrition at the right time increases intelligence, possibly by boosting the physical growth of the brain.

Although average intelligence has increased, it is not clear whether everyone has benefited. Have the very intelligent pushed up the average by becoming even brighter, has the increase in IQ been across the board, or have those at the lower end benefited the most? Many of the explanations that have been put forward for the phenomenon require either an across-the-board increase in intelligence, or for those at the top end to have pulled further ahead. But if nutrition is the explanation, then the increase in IQ would be mainly in deprived groups who, over time, have gained access to better diets.

In the new research, Dr Roberto Colom and his colleagues looked at the IQ and lifestyles of two comparable groups of seven-year-old boys, 30 years apart. The results showed that the gains in IQ were seen among the deprived boys. Their increase in IQ scores was nine times that of the other group.

"The study shows that intelligence gains are mainly concentrated in the bottom and medium sections," says Dr Colom, whose research is to be published in the journal Intelligence. "The gains are progressively smaller as we move toward the upper half. The tendency is impressive."

The finding, that nutrition is the most likely explanation for the rise in IQ, is supported by other evidence. Researchers have established a link between height, brain size and intelligence, and, if nutrition is the explanation for gains in intelligence, then it should have an impact on height and brain size. And it does: the second half of the 20th century saw an increase in average brain size and in height in Britain. Several studies have also shown that poor nutrition reduces brain size.

"The relationship between head size and IQ has long been a subject of controversy. Popular writers have rightly objected to the crude and biased means that 19th-century scholars used to establish this correlation, which were based on head size and contour," says Professor Ceci. "But modern neuro-imaging techniques demonstrate that cranial volume is correlated with IQ. Evidence also comes from studies of the helmet sizes of members of the armed services, whose IQs are measured during basic training."

Just what kind of nutrition could be involved is far from clear. Some research suggests that it is not just the quantity of food that has an effect on IQ, but the quality. Some studies indicate that diets with healthy iron and zinc levels are related to higher scores on intelligence tests, while others have linked intellectual performance to the type of fat found most commonly in fish - omega-3 fatty acids.

Omega-3s play a key part in the development of the outer membrane of brain cells, through which all nerve signals pass. It is suggested that, as learning and memory forge new connections between nerve cells, new membranes need to be made to sheathe them.

One British study, of 360 babies born prematurely, found that those fed standard, pre-term formula milk, rather than a nutrient-enriched formula, had reduced verbal IQ scores when they reached seven to eight years of age.

In another study, in Norfolk, Virginia, children born to mothers who had been given extra nutrients during pregnancy had higher IQs than other children three years later. The supplements used were vitamins B1, B2, B3 and iron.

A number of other researchers have also found links between nutrients in the diet and the brain. Low levels of dietary zinc have been linked to a range of cognitive and social- emotional problems.

A key question yet to be answered is whether the beneficial effect of diet stops when the brain is fully grown, or whether it can continue thereafter. Some research suggests that it may also be possible to boost alertness and memory by eating certain foods. Supplementation with choline, the B vitamin found in eggs, for example, has been shown to boost memory.

Perhaps the most convincing evidence that dietary changes can boost IQ comes from research based on students in New York, and reported in Psychology Today. Researchers examined IQ scores before and after preservatives, dyes, colourings and artificial flavours were removed from lunch meals. They found a 14 per cent improvement, and the improvement was greatest for the weakest students. Before the dietary changes, 120,000 of the students were performing two or more grade levels below average. After, the figure dropped to 50,000.