Few questions in psychology generate as much debate as whether intelligence is fixed or malleable. The idea that IQ is set in stone — hardwired by genetics and sealed by early childhood — persists in popular culture, but the scientific picture is considerably more nuanced. Decades of research show that IQ scores can and do change, though the mechanisms, magnitude, and permanence of those changes vary widely. This article reviews what the evidence supports.
Genetic Determinants of IQ
Twin and adoption studies consistently estimate the heritability of IQ at 50–80% in adults, making it one of the most heritable behavioral traits measured. However, heritability is frequently misunderstood. It describes how much of the variation in IQ within a population is attributable to genetic differences — it does not mean that 80% of any individual’s IQ is “genetic” or that the remaining 20% is all that can be influenced.
Research on the genetic and environmental origins of cognitive abilities shows that genetic and environmental contributions operate at different levels of the cognitive hierarchy. General intelligence (g) shows the highest heritability, while specific abilities — verbal fluency, spatial reasoning, processing speed — are more environmentally sensitive. Targeted interventions can shift specific cognitive skills even when the overall g factor is harder to move.
Heritability estimates are also population-specific and context-dependent. In environments with high inequality, environmental factors explain more variance. In environments where everyone has access to adequate nutrition, education, and stimulation, genetic differences explain more. This is why the question of whether IQ can be increased cannot be answered without specifying: for whom, from what baseline, and under what conditions.
The Effect of Education on IQ
The evidence that education raises IQ is among the strongest in the field. Ritchie and Tucker-Drob’s (2018) meta-analysis pooled 142 effect sizes from 42 datasets and over 600,000 participants, concluding that each additional year of education raises IQ by approximately 1 to 5 points, with a best central estimate of about 1–3 points per year. The effect held across designs, age groups, and the type of education. Critically, it persisted in studies using natural experiments — situations in which compulsory schooling laws forced students to remain in school for additional years, removing the selection bias that contaminates most observational data (i.e., the suspicion that smarter people stay in school longer).
Schooling appears to affect both crystallized abilities (vocabulary, general knowledge) and, to a lesser extent, fluid reasoning. The mechanisms likely include sustained practice in abstract thinking, exposure to complex problem-solving, and the development of cognitive strategies that transfer across domains. Research summarized in our overview of how education improves intelligence has converged on this picture across decades.
The Flynn Effect and Its Implications
Among the strongest evidence that IQ can change is the Flynn effect: the well-documented finding that population-level IQ scores rose by approximately 3 points per decade throughout most of the 20th century. Analysis of trends in the Flynn effect shows gains across virtually every country tested, with the largest increases occurring on tests of fluid intelligence — the abilities most often assumed to be biologically fixed.
The gains are too rapid to be explained by genetic changes; evolution does not work that fast. Instead, they likely reflect environmental improvements: better nutrition, reduced exposure to lead and other neurotoxins, more years of schooling, greater cognitive stimulation through media and technology, and smaller family sizes (allowing more parental investment per child). Recent evidence on cohort trends in cognitive functioning suggests the Flynn effect has slowed or reversed in several developed countries since the 1990s. Whatever the cause of that “negative Flynn effect” turns out to be, it is itself proof that population-level IQ responds to environmental conditions in both directions.
Nutrition, Diet, and IQ
The evidence for nutritional effects on cognition is strongest during prenatal development and early childhood, when the brain is most rapidly growing. Protzko, Aronson, and Blair’s (2013) meta-analysis of early-childhood interventions, drawn from their Database of Raising Intelligence, identified four classes of intervention that reliably raise IQ in young children: nutritional supplementation (when there is an existing deficit), interactive reading with a parent, sending a child to preschool, and explicit cognitive training in low-resource settings. Effect sizes for these are typically 4–7 IQ points — modest but meaningful, and replicated.
- Prenatal nutrition: Research on vitamin D during pregnancy links maternal deficiency to lower cognitive scores in offspring. Early-nutrition research consistently shows that adequate protein, iron, iodine, and omega-3 fatty acids during critical developmental windows are associated with higher cognitive outcomes.
- Breastfeeding: Studies on maternal milk feeding in preterm infants show measurable benefits for neurodevelopment, though separating the effects of milk composition from confounding variables (maternal IQ, socioeconomic status, parenting quality) remains challenging.
- Adult nutrition: The Mediterranean diet and cognitive function literature suggests dietary patterns rich in antioxidants, healthy fats, and micronutrients are associated with slower cognitive decline in aging. Whether these effects represent IQ “increases” or simply prevention of decline is an important distinction.
- Micronutrient supplementation: In populations with existing deficiencies, supplementation (particularly iron and iodine) can produce IQ gains of 5–15 points. In well-nourished populations, the effects are minimal to nonexistent. This pattern illustrates the principle that environmental interventions work best where there is an existing environmental deficit.
Environmental Toxins and IQ
Removing cognitive harm is, in effect, another way to “raise” IQ — and the evidence here is substantial. Air pollution has been linked to lower IQ scores, reduced processing speed, and accelerated cognitive decline. Fine particulate matter (PM2.5) crosses the blood-brain barrier and causes neuroinflammation, with effects documented across all age groups. Research on early-life chemical exposure estimates that preventable environmental exposures — lead, mercury, organophosphate pesticides, and flame retardants — collectively account for millions of IQ points lost across the U.S. population. Prenatal exposure to phthalates in plastics and personal-care products has also been associated with lower cognitive scores in children.
The policy implication is clear: reducing population-level exposure to neurotoxins is one of the most effective and most evidence-based strategies for raising cognitive ability at scale. The phase-out of leaded gasoline in the 1970s–1990s is estimated to have contributed several IQ points to the cohort effects observed in the Flynn data.
The Efficacy of Brain Training
For brain training, the evidence becomes considerably weaker — and more contested. The modern brain-training era began with Jaeggi, Buschkuehl, Jonides, and Perrig’s (2008) PNAS paper, which reported that training on a dual n-back working-memory task produced gains in fluid intelligence (Gf). The result attracted considerable attention: a brief training task that increased the gold-standard measure of “raw” cognitive ability. A wave of commercial products followed, including Lumosity, BrainHQ, and CogMed.
The replication record has been unkind. Melby-Lervåg, Redick, and Hulme’s (2016) meta-analysis of working-memory training is the field’s most rigorous summary: across 87 studies and dozens of training protocols, training reliably improved performance on the trained task and on closely similar tasks. It did not reliably improve performance on independent measures of fluid intelligence, reading, or other “far transfer” outcomes once active control groups were used. The pattern is consistent: people get better at what they practice, but those gains do not generalize to broader cognitive ability.
The wider scientific community’s verdict crystallized in two competing 2014 consensus statements. The Stanford Center on Longevity and Max Planck Institute for Human Development released a statement signed by more than 70 cognitive scientists arguing that there was “no compelling scientific evidence” that commercial brain training improves general cognitive performance in everyday life. A counter-statement signed by some researchers in the field disagreed. In 2016 the U.S. Federal Trade Commission settled with Lumos Labs over Lumosity’s advertising, fining the company $2 million for deceptive marketing. Subsequent transfer-test studies — for example Stojanoski and colleagues’ 2018 work on token-tracking training — continued to find that improvements stay narrowly within the trained skill.
One area where modest evidence persists is working-memory training in children with markedly low working memory (such as those with ADHD or specific learning difficulties). Even there, transfer to broad IQ remains contested.
Physical Exercise and IQ
Among “lifestyle” interventions, exercise has the strongest evidence — particularly for children. Morales and colleagues’ (2024) meta-analysis in Pediatrics pooled randomized trials of structured exercise programs in children and adolescents and reported a mean IQ gain of approximately 4 points — comparable to roughly one additional year of schooling. The effect was largely independent of starting IQ and intervention duration; effective programs typically involved 30–60 minutes of moderate-to-vigorous activity, 3–5 days per week, sustained for several months.
For adults, research on physical activity and cognitive health shows that even light-intensity activity within hours of testing can transiently improve processing speed by an amount equivalent to several years of cognitive aging. Chronic exercise is associated with larger hippocampal volume, improved executive function, and reduced dementia risk. The likely mechanisms include increased cerebral blood flow, hippocampal neurogenesis, BDNF upregulation, and improved sleep — all of which support the neural substrates of cognition.
Epigenetic Influences on IQ
A recent development in intelligence research involves epigenetic mechanisms — changes in gene expression that occur without alterations to the DNA sequence itself. Environmental factors like stress, nutrition, toxin exposure, and even parenting behavior can modify epigenetic markers (particularly DNA methylation patterns) that influence the expression of genes involved in neural development and neurotransmitter function. Specific modifications to dopamine D2 receptor genes, for example, have been associated with measurable differences in cognitive ability and are responsive to environmental conditions. While this field is still young, it provides a molecular framework for understanding how IQ can be influenced by environment even in the context of high heritability.
What Works: A Summary
| Intervention | Evidence Strength | Estimated Effect | Who Benefits Most |
|---|---|---|---|
| Education (additional years) | Strong | +1–5 points per year | Children and adolescents |
| Removing neurotoxins (lead, pollution) | Strong | +2–7 points (population level) | Exposed populations |
| Micronutrient supplementation | Strong (in deficient populations) | +5–15 points | Malnourished children |
| Structured aerobic exercise | Strong (children) | ~+4 points | Children/adolescents |
| Prenatal health optimization | Moderate–Strong | Variable (prevents deficits) | Developing fetuses |
| Interactive reading with parents | Moderate | +4–6 points | Preschoolers |
| Mediterranean-style diet | Moderate | Slowed decline; modest gains unclear | Aging adults |
| Brain training apps | Weak | Task-specific; no IQ transfer | Limited evidence for anyone |
| Music lessons | Weak–Moderate | Small and contested | Children |
Frequently Asked Questions
Can adults increase their IQ?
Modestly. Education, regular exercise, social engagement, and treating modifiable health conditions (sleep apnea, hypertension, depression) all support cognitive performance. Substantial IQ gains in well-resourced adults are rare. The realistic adult goal is preservation and modest improvement, not transformation.
Do brain training apps work?
For improving the specific games played, yes. For raising general intelligence or improving everyday cognitive performance, the evidence is weak. The most rigorous meta-analyses (Melby-Lervåg, Redick & Hulme, 2016) find no reliable far-transfer to fluid intelligence once proper active control groups are used.
How much does education increase IQ?
About 1–3 IQ points per additional year of schooling on average, with effects up to 5 points in some studies (Ritchie & Tucker-Drob, 2018). The effect is one of the most replicable in the field.
Does exercise raise IQ in children?
Yes. The 2024 Morales et al. meta-analysis in Pediatrics reported that structured exercise programs in children and adolescents produce a mean IQ gain of about 4 points, comparable to a year of schooling. Adult evidence is weaker but still suggestive.
Will reading more raise IQ?
Frequent reading expands vocabulary and general knowledge — both of which contribute to crystallized IQ scores. The size of the effect in adults is modest. Reading is most effective as an intervention in early childhood, where parental reading is consistently linked to better cognitive outcomes.
Are IQ gains from interventions permanent?
Some are. Education-related gains tend to persist as long as the underlying skills are used. Gains from removing neurotoxins or correcting nutritional deficiencies are durable. Gains from short-term interventions (a single training program) typically fade once the practice stops, especially if no real-world skill is built on top.
Conclusion
IQ is neither fully fixed nor freely malleable. The answer to whether IQ can be increased is that it depends on the starting point, the individual’s age, and the specific intervention. The most robust evidence supports education, toxin reduction, adequate prenatal and early-childhood nutrition, and structured exercise (especially in children) as reliable levers for raising cognitive ability. Commercial brain-training apps remain poorly supported despite their marketing. For adults in well-resourced environments, the realistic goal is more often cognitive maintenance — protecting existing abilities through exercise, diet, sleep, and continued intellectual engagement — rather than substantial IQ gains. Further work addresses the epigenetic pathways through which environmental factors shape gene expression, potentially opening new avenues for targeted cognitive interventions.
References
- Jaeggi, S. M., Buschkuehl, M., Jonides, J., & Perrig, W. J. (2008). Improving fluid intelligence with training on working memory. Proceedings of the National Academy of Sciences, 105(19), 6829–6833. https://doi.org/10.1073/pnas.0801268105
- Melby-Lervåg, M., Redick, T. S., & Hulme, C. (2016). Working memory training does not improve performance on measures of intelligence or other measures of “far transfer”: Evidence from a meta-analytic review. Perspectives on Psychological Science, 11(4), 512–534. https://doi.org/10.1177/1745691616635612
- Morales, J. S., Valenzuela, P. L., Martínez-de-Quel, Ó., Sánchez-Sánchez, J. L., Muntaner-Mas, A., Erickson, K. I., Carbonell-Baeza, A., Ortega, F. B., & Jiménez-Pavón, D. (2024). Exercise interventions and intelligence in children and adolescents: A meta-analysis. Pediatrics, 154(6), e2023064771. https://doi.org/10.1542/peds.2023-064771
- Protzko, J., Aronson, J., & Blair, C. (2013). How to make a young child smarter: Evidence from the database of raising intelligence. Perspectives on Psychological Science, 8(1), 25–40. https://doi.org/10.1177/1745691612462585
- Ritchie, S. J., & Tucker-Drob, E. M. (2018). How much does education improve intelligence? A meta-analysis. Psychological Science, 29(8), 1358–1369. https://doi.org/10.1177/0956797618774253