Sugar

What it is

Sugar commonly refers to sucrose, a disaccharide carbohydrate composed of equal parts glucose and fructose [1]. It is naturally found in plants such as sugar cane and sugar beet, and is widely added to processed foods, desserts, and sweetened beverages [2]. In nutritional guidelines, added sugars and free sugars describe sugars introduced to foods during manufacturing, cooking, or preparation, distinct from sugars naturally occurring in whole fruits and unflavored milk [2].

How it might work

Proposed, not established: when children consume sucrose, it is rapidly digested into glucose and fructose, causing an initial rise in circulating blood glucose and triggering insulin secretion [3]. Parents and earlier theorists hypothesized that subsequent rapid drops in blood glucose (reactive hypoglycemia) or adrenaline surges might trigger restlessness, irritability, and hyperactivity [1]. Sugar also stimulates dopamine signaling in brain reward pathways, which makes sweet tastes appealing to children [4]. However, controlled metabolic and behavioral studies show that typical sugar consumption does not produce behavioral instability or cognitive impairment [1] [3].

What the research says

Child behavior and hyperactivity. A landmark 1995 meta-analysis in JAMA evaluated 16 reports covering 23 within-subject double-blind placebo-controlled trials [1]. The analysis evaluated 14 measurement constructs, including direct behavioral observation, continuous performance tests, and teacher ratings [1]. The weighted mean effect sizes ranged from -0.14 for direct observations to +0.30 for academic tests, with the 95% confidence interval for all 14 measures including zero [1]. The authors concluded that sugar does not affect behavior or cognitive performance in children [1].

In a 9-week double-blind controlled trial, 48 children (including 23 school-age children described by their parents as sensitive to sugar and 25 preschool children) rotated through three 3-week diets high in sucrose, aspartame, or saccharin placebo [3]. For the sugar-sensitive children, there were no significant differences across any of 39 behavioral and cognitive variables [3]. For the preschool group, only 4 of 31 measures differed significantly, with no consistent pattern [3].

Parental expectancy. A double-blind challenge trial demonstrated that parental perception accounts for reports of hyperactivity [5]. Thirty-five mothers and their 5- to 7-year-old sons, reported to be sugar-sensitive, were randomly assigned to two groups where all boys received an identical placebo sweetened with aspartame [5]. Mothers told their sons received sugar rated them as significantly more hyperactive and were observed to exercise more physical control, criticism, and closer observation than mothers told their sons received placebo [5].

Observational ADHD associations. Observational studies frequently observe higher rates of sugar and sweet beverage intake among youth with ADHD symptoms [6] [7]. A 2020 meta-analysis of seven observational studies (25,945 participants) reported a pooled odds ratio of 1.22 (95% CI 1.04 to 1.42) for ADHD symptoms, although heterogeneity was high (I² = 81.9%) [6]. A 2026 meta-analysis of nine observational studies (461,109 participants) found an odds ratio of 1.23 (95% CI 1.02 to 1.48) for sugar-sweetened beverage intake, but the prediction interval crossed null (0.79 to 1.90) and potential publication bias was present [7]. Systematic reviews note that these associations reflect confounding and reverse causation rather than direct causal effects [8] [4].

Doses used in studies

In the 9-week dietary trial, preschool children consumed an average of 5,600 mg of sucrose per kilogram of body weight per day on the sucrose diet, and sugar-sensitive school-age children consumed 4,500 mg per kilogram daily [3]. Acute challenge trials in the JAMA meta-analysis administered single oral sucrose doses typically ranging from 1 to 2 g per kilogram of body weight [1]. These are research doses used to test behavioral thresholds, not dietary recommendations.

Safety and interactions

Side effects. Common adverse effects of high sugar intake include dental caries, weight gain, and gastrointestinal symptoms such as abdominal cramping or loose stools after acute large intakes [2] [9].

Upper limits. The World Health Organization recommends limiting free sugars to less than 10% of total daily energy intake, with additional health benefits below 5% (approximately 25 grams or 6 teaspoons per day for a standard 2,000-calorie diet) [2]. An umbrella review of 73 meta-analyses recommended limiting free sugar intake to below 25 g/day and keeping sugar-sweetened beverages to less than one serving per week (200 to 355 mL/week) [2]. There is no established acute toxic dose, but long-term excess is associated with increased cardiometabolic disease risk [2].

Medicine interactions. Rapid absorption of sucrose directly raises blood glucose, which directly affects dosing requirements for insulin and oral hypoglycemic drugs such as sulfonylureas [2]. Medications such as acarbose and miglitol inhibit alpha-glucosidase enzymes and impair sucrose breakdown in the gut.

Pregnancy and breastfeeding. High intake of added sugars and sugar-sweetened beverages during pregnancy is associated with increased risk of gestational diabetes, excessive gestational weight gain, and preeclampsia [2] [9]. Moderate sugar intake as part of a balanced diet has not been shown to harm breastfeeding, but high added sugar intake provides empty calories without essential nutrients.

Kidney, liver, and metabolic conditions. High intake of added sugars and fructose is associated with non-alcoholic fatty liver disease, hyperuricemia and gout, kidney disease progression, and poor glycemic control in type 2 diabetes [2] [9]. Individuals with hereditary fructose intolerance must strictly avoid sucrose.

Caveats and open questions

The double-blind trials establishing that sugar does not cause hyperactivity were largely conducted in the 1980s and 1990s, using artificial sweeteners like aspartame and saccharin as control placebos [1] [3]. While these trials convincingly excluded large behavioral effects, minor effects in rare, uncharacterized subgroups cannot be completely ruled out by group-level analyses [1].

Observational studies linking added sugar or sweet drinks to ADHD symptoms do not establish causation [6] [4]. Children with ADHD or executive function challenges may have greater difficulty with impulse control around palatable foods, and family stressors or dietary habits may act as unmeasured confounders [8] [4]. Most modern observational literature evaluates sugar-sweetened beverages rather than isolated solid sucrose [7].