Does Sugar Make You Smarter? What the Research Shows

No, sugar does not make you smarter. When researchers gave children sugar or a sugar-free placebo without anyone knowing which was which, a meta-analysis of 23 such studies found no reliable effect on thinking or behaviour: every pooled effect size had a confidence interval that included zero.

The opposite claim, that sugar makes people less intelligent, is also weaker than headlines suggest. In large cohort studies, heavy sugar intake goes with IQ scores that are lower by roughly 1.5 to 2.5 points, but those studies cannot separate sugar from everything else that travels with a high-sugar diet. This page covers the blinded trials, the "sugar rush" myth, what the cohort studies found, and why the confounds matter. It describes research and is not diet advice.

The cleanest way to test sugar is a "double-blind" trial, in which neither the participants nor the researchers know who received sugar and who received an artificial sweetener. Without blinding, the belief that sugar changes behaviour can colour what parents, teachers and children report.

In 1995, Mark Wolraich, David Wilson and J. Wade White pooled every blinded, placebo-controlled sugar study they could find. Sixteen reports, covering 23 studies, met their criteria. They examined 14 different outcomes, from directly observed behaviour to academic test performance. The average effects ranged from -0.14 standard deviations for observed behaviour to +0.30 for academic tests, and the 95% confidence interval for every one of them included zero. On the IQ scale, where one standard deviation is 15 points, even the most favourable estimate would be about 4.5 points, and the data could not distinguish it from no effect at all. The authors concluded that sugar does not affect children's behaviour or cognitive performance, while noting that a small effect, or an effect in a subset of children, could not be ruled out.

The strongest single trial came a year earlier. Wolraich and colleagues placed 25 preschool children and 23 school-age children whose parents described them as sensitive to sugar on three diets, each for three weeks: high in sucrose, low in sucrose with aspartame, or low in sucrose with saccharin as a placebo. The preschoolers ate an average of 5.6 grams of sucrose per kilogram of body weight per day on the sugar diet, far more than a normal diet supplies. For the supposedly sugar-sensitive children, none of 39 behavioural and cognitive measures differed between the diets. For the preschoolers, 4 of 31 measures differed, with no consistent pattern.

If sugar does so little, why do so many parents swear by its effects? One answer is expectation. Hoover and Milich recruited 35 boys aged 5 to 7 whose mothers considered them "sugar sensitive". Every boy drank a placebo sweetened with aspartame, but half of the mothers were told their son had just had a large dose of sugar. Those mothers rated their sons as significantly more hyperactive. Videotapes showed that they also hovered closer, and tended to criticise and talk to their sons more, than mothers in the control group.

Context does the rest. Sugar is served at parties, holidays and other exciting events, so the excitement and the cake arrive together.

The adult version of the myth is the "sugar rush", the idea that a sugary snack sharpens mood and energy. Mantantzis and colleagues pooled 176 effect sizes from 31 studies with 1,259 participants and found no positive effect of carbohydrates on any aspect of mood at any point after eating them. Within the first hour, people who had taken carbohydrate reported more fatigue and less alertness than people who had taken a placebo.

A narrower question is whether a glucose drink helps memory in the short term. A research literature on the "glucose memory facilitation effect", reviewed by Smith and colleagues in 2011, reports that raising blood glucose can improve some memory tasks under some conditions, especially in older adults and people with compromised memory. That is a brief change in task performance, and it says nothing about intelligence. Glucose, ketones and whether the brain "needs sugar" are covered in our page on fasting and IQ.

The evidence that worries people comes from observational studies, which follow large groups and compare those who eat more sugar with those who eat less.

• Project Viva (United States): Cohen and colleagues followed 1,234 mother-child pairs. Each additional 15 grams a day of sucrose in the mother's diet during pregnancy was associated with a 1.5-point lower non-verbal score on the Kaufman Brief Intelligence Test in mid-childhood (median age 7.7). Each daily serving of sugar-sweetened drinks in early childhood was associated with a 2.4-point lower verbal score. Fruit intake went with higher scores, while fructose and fruit juice showed no association. After correction for the many comparisons tested, the only association that held was between the mother's diet soda intake and her child's verbal score, which points away from sugar itself.

• ALSPAC (United Kingdom): Northstone and colleagues studied 3,966 children whose parents reported their diets from age 3. A one-standard-deviation increase in a "processed" diet pattern, high in fat and sugar, at age 3 was associated with an IQ 1.67 points lower at age 8.5, after adjustment for a range of confounders. A "health-conscious" pattern at 8.5 went with an IQ 1.2 points higher.

• Framingham (United States): Pase and colleagues examined over 4,000 adults. Compared with less than one sugary drink a day, one to two a day was associated with lower total brain volume and poorer episodic memory. The authors expressed the gap in delayed story recall as equivalent to 5.8 years of brain ageing for one to two drinks a day and 11.0 years for more than two. Daily fruit juice showed similar associations.

These are small differences, and in the Framingham study the outcome was memory and brain volume rather than IQ. The Framingham authors also stressed that their cross-sectional design precludes conclusions about causation.

Sugar intake is tangled up with almost every variable that predicts test scores. Diets high in sugary drinks and processed food are more common in families with lower incomes and less parental education, and parental education and IQ are among the strongest predictors of a child's IQ. Studies adjust for these factors, but the adjustment is only as good as the measures, and residual confounding of 1 or 2 points is entirely plausible.

Reverse causation is another possibility. People with higher IQs tend to have more education and better health habits, so a modest IQ advantage could lead to lower sugar intake, rather than the other way round. In older adults, sugary drink intake also travels with diabetes, obesity and high blood pressure, each of which has its own links to brain health. The Project Viva finding that diet soda, which contains no sugar, was the most robust association is a reminder of how hard it is to isolate one ingredient.

What is missing is a randomised trial that changes sugar intake for years and then measures IQ. Without one, the honest summary is that blinded short-term trials show no effect, and long-term observational links are small and probably confounded. The broader evidence on food and children's intelligence is in our overview of whether diet or nutrition affects IQ. Micronutrients such as zinc and iodine are a different story, because deficiency of a specific nutrient is easier to test in trials than a general diet pattern.

No trial shows that sugar raises intelligence. A glucose drink can briefly help some memory tasks in some studies, but carbohydrates also tend to make people feel more tired and less alert within the first hour.

Blinded trials say no. A meta-analysis of 23 studies found no reliable effect of sugar on children's behaviour or cognition, and an experiment showed that mothers who merely believed their son had eaten sugar rated him as more hyperactive.

Cohort studies link heavy sugar intake to IQ scores about 1.5 to 2.5 points lower, but these studies cannot rule out family income, parental education and other confounds. No long-term randomised trial has tested it.

A meta-analysis of 31 studies found no improvement in mood or energy after eating carbohydrates. People reported more fatigue and less alertness in the first hour than after a placebo.

A paediatrician, family doctor or registered dietitian can give advice based on your child's health and growth. Concerns about attention or behaviour are worth raising with the child's doctor, whatever the diet.

Sugar does not make you smarter, and the best blinded trials show it does not make children hyperactive or less able to think in the short term either. The long-term picture is less certain: large cohort studies link heavy sugar intake to slightly lower IQ and memory scores, but family background and general health explain at least part of that link. If you want a trustworthy measure of your reasoning ability rather than a guess based on your diet, take a professionally developed IQ test.

1. Wolraich, M. L., Wilson, D. B., & White, J. W. (1995). The effect of sugar on behavior or cognition in children: A meta-analysis. JAMA, 274(20), 1617-1621. [doi.org/10.1001/jama.1995.03530200053037](. doi.org

2. Wolraich, M. L., Lindgren, S. D., Stumbo, P. J., Stegink, L. D., Appelbaum, M. I., & Kiritsy, M. C. (1994). Effects of diets high in sucrose or aspartame on the behavior and cognitive performance of children. The New England Journal of Medicine, 330(5), 301-307. [doi.org/10.1056/NEJM199402033300501](. doi.org

3. Hoover, D. W., & Milich, R. (1994). Effects of sugar ingestion expectancies on mother-child interactions. Journal of Abnormal Child Psychology, 22(4), 501-515. [doi.org/10.1007/BF02168088](. doi.org

4. Mantantzis, K., Schlaghecken, F., Sünram-Lea, S. I., & Maylor, E. A. (2019). Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood. Neuroscience & Biobehavioral Reviews, 101, 45-67. [doi.org/10.1016/j.neubiorev.2019.03.016](. doi.org

5. Smith, M. A., Riby, L. M., van Eekelen, J. A., & Foster, J. K. (2011). Glucose enhancement of human memory: A comprehensive research review of the glucose memory facilitation effect. Neuroscience & Biobehavioral Reviews, 35(3), 770-783. [doi.org/10.1016/j.neubiorev.2010.09.008](. doi.org

6. Cohen, J. F. W., Rifas-Shiman, S. L., Young, J., & Oken, E. (2018). Associations of prenatal and child sugar intake with child cognition. American Journal of Preventive Medicine, 54(6), 727-735. [doi.org/10.1016/j.amepre.2018.02.020](. doi.org

7. Northstone, K., Joinson, C., Emmett, P., Ness, A., & Paus, T. (2012). Are dietary patterns in childhood associated with IQ at 8 years of age? A population-based cohort study. Journal of Epidemiology and Community Health, 66(7), 624-628. [doi.org/10.1136/jech.2010.111955](. doi.org

8. Pase, M. P., Himali, J. J., Jacques, P. F., DeCarli, C., Satizabal, C. L., Aparicio, H., Vasan, R. S., Beiser, A. S., & Seshadri, S. (2017). Sugary beverage intake and preclinical Alzheimer's disease in the community. Alzheimer's & Dementia, 13(9), 955-964. [doi.org/10.1016/j.jalz.2017.01.024](. doi.org

Hero image: Sugar cubes in India 03, by Pinakpani, CC BY 4.0. Via Wikimedia Commons.