Growth Science
Our sleep guide explains why sleep is the main way everyday habits touch growth hormone, and our calcium guide already notes that soft drinks tend to crowd out calcium-rich drinks. This piece answers the narrower question parents actually search: does caffeine itself stunt a child's growth? It covers where the belief came from, what studies of growing bones found, the one pathway with real data behind it (sleep), and how much caffeine is in common drinks compared with the guidance for kids.
Caffeine in a 12-oz Drink vs. a Child's Daily Limit
Typical amounts from FDA data, plotted against Health Canada's daily maximum for kids
Where the "Caffeine Stunts Growth" Belief Comes From
A Smithsonian Magazine history traces the belief to Postum, an early-1900s coffee substitute whose ads warned parents off coffee for children, including a 1933 ad claiming it hampers development and growth. The idea spread through culture, not through research.
Caffeine does slightly reduce how well the gut absorbs calcium, and calcium builds bone. That kernel of truth made the story sound plausible. The question is how big the effect is, and the research says it is very small.
What Actually Determines Height
Genetics accounts for roughly 80% of the variation in height. The remaining 20% or so covers diet quality, sleep, general health, and childhood illness — not a daily cup of tea or a can of soda.
As our growth plates guide explains, height is set by sex hormones driving growth plates to lengthen bone, then signaling those same plates to fuse once puberty finishes. Caffeine isn't part of that hormonal signaling, which is why the only plausible routes to a growth effect are indirect ones: bone-building minerals and sleep.
What the Research Shows About Caffeine and Growing Bones
If caffeine stunted growth through bone, it should show up as weaker bone gain in teens who consume more of it. Here is how the chain of reasoning holds up against the evidence.
Soda, tea, coffee, and energy drinks are the main sources
A clear but very small effect in physiology studies
As little as 1-2 tablespoons covers the difference
Adolescent studies found no link to bone gain or density
Three lines of evidence point the same way. A longitudinal study of American girls followed from ages 12 to 18 sorted them into three groups by dietary caffeine intake and measured bone with DXA scans. There were no significant differences in total-body bone gain across those years or in hip bone density at age 18. A more recent analysis of national survey data on nearly 3,000 children and adolescents found no significant difference in femur bone density in the highest-intake group, and a separate genetic (Mendelian randomization) analysis did not support a causal link between caffeine and bone density in this age group. And a review of the physiology by calcium researcher Robert Heaney found a clear but very small effect of caffeine on intestinal calcium absorption, with no effect on total daily urinary calcium loss, small enough to be fully offset by 1-2 tablespoons of milk.
Heaney also pointed out why some observational studies have linked caffeinated drinks with lower bone mass: people who drink more caffeinated beverages tend to drink less milk, and the concerning findings came from populations with low calcium intake. That fits the displacement concern in our calcium guide. The practical issue is a can of soda taking the place of a glass of milk, not the caffeine blocking the milk.
What "no evidence" does and doesn't mean. Nobody has randomly assigned children to years of daily caffeine versus none, for obvious ethical reasons, so the best evidence is observational and genetic. The studies above are consistent and reassuring, but they reflect typical intakes, not heavy daily energy-drink use, and they can't rule out small effects at high doses. "No credible evidence of stunting" is the accurate statement; "proven harmless" is not.
The Real Concern: Sleep
The one pathway with solid data in young people is sleep. In a study of 98 adolescents aged 11-17 who wore at-home sleep EEG monitors for seven consecutive nights and logged their caffeine each day, caffeine was linked to taking longer to fall asleep and to shorter, less efficient sleep with less REM. The effects were driven by afternoon and evening use.
There's an important nuance for the growth question. Our sleep guide explains that the largest growth hormone pulse of the day comes during deep sleep. In this study, caffeine use wasn't associated with the amount of deep sleep, and the researchers noted that effects on deep sleep varied between individuals. So the sleep route is plausible but unproven: no study has followed a chain from caffeine to shorter sleep to lower growth hormone to a shorter adult height. What the data does support is simpler. Afternoon and evening caffeine costs teens real minutes of sleep, which lines up with the 2 p.m. cutoff in our sleep guide.
How Much Caffeine Is in Common Drinks, and What Guidance Says
The chart above shows why the practical conversation is about amount, not height. Here is how the main sources compare with a child's limit.
Health Canada recommends no more than 2.5 mg of caffeine per kilogram of body weight per day for children and adolescents, which works out to about 75 mg for a 30 kg (66 lb) child and 125 mg for a 50 kg (110 lb) teen. It calls the figure precautionary because data in children are limited. In the U.S., the FDA's 400 mg figure applies to healthy adults, the FDA advises against energy drinks for children and teens, and the Dietary Guidelines for Americans say caffeinated drinks should be avoided before age 2. Beyond sleep, the FDA lists faster heart rate, palpitations, higher blood pressure, anxiety, digestive problems, and dehydration as effects of too much caffeine in children and teens. None of those involve height, but each is a genuine reason to keep amounts low.
A Separate Question: Caffeine During Pregnancy
Don't confuse this with a child's own intake. You may come across a 2022 JAMA Network Open study reporting that children whose mothers had higher blood caffeine levels during pregnancy were slightly shorter at ages 4 to 8. In the contemporary cohort of 788 children, those in the highest quartile of maternal caffeine had a lower height z score than those in the lowest (-0.21). That is a question about exposure before birth, the study was observational, and the authors state the clinical implications are unclear. It says nothing about whether a child drinking caffeine will grow less. Anyone who is pregnant or planning pregnancy should talk with their health care provider about caffeine, as the FDA advises.
What This Means For You
Making sure calcium intake is adequate through milk or other foods, as covered in our milk guide and calcium guide
The practical takeaway: caffeine doesn't stunt growth by any evidence we have — height is roughly 80% genetic, adolescent studies found no link between caffeine and bone gain, and the calcium effect is small enough that a splash of milk offsets it. The honest caveats are that long-term controlled trials in children don't exist, and that the real costs of caffeine are lost sleep and a daily amount that can overshoot a child's limit quickly. For the sleep biology behind that, see our sleep guide, for the calcium side see our calcium guide, and for what actually sets the ceiling on height see our growth plates guide.
Frequently Asked Questions
Does caffeine stunt growth?
No study has shown that it does. Height is roughly 80% determined by genetics, and research on adolescents found no link between caffeine intake and bone gain or bone density. The honest caveat is that long-term controlled trials giving children caffeine don't exist, so the evidence is observational.
Does caffeine block calcium and weaken bones in teens?
Only very slightly. Caffeine has a small effect on calcium absorption that as little as 1-2 tablespoons of milk can offset, and a study that followed girls from ages 12 to 18 found no difference in bone gain between low, moderate, and high caffeine intake groups. The more realistic concern is caffeinated drinks replacing milk in a teen's day.
How much caffeine is okay for kids and teens?
Health Canada recommends no more than 2.5 mg per kilogram of body weight per day for children and adolescents, about 75 mg for a 30 kg child and 125 mg for a 50 kg teen, and calls this precautionary. The FDA's 400 mg figure is for healthy adults, and the American Academy of Pediatrics discourages caffeine for children and adolescents. A pediatrician can advise on your child's situation.
Are energy drinks worse than coffee or soda for kids?
Per the FDA, a 12-ounce energy drink contains 41 to 246 mg of caffeine, similar to regular coffee at 113 to 247 mg and higher at the top end than soft drinks at 23 to 83 mg. Medical experts advise against energy drinks for children and teens because of their combined sugar and caffeine levels, according to the American Academy of Pediatrics.
If caffeine doesn't stunt growth, why do doctors still say to limit it?
Because the documented effects are elsewhere. The FDA lists faster heart rate, palpitations, higher blood pressure, anxiety, sleep problems, digestive problems, and dehydration from too much caffeine in children and teens, and a sleep-EEG study of adolescents linked afternoon and evening caffeine to less total sleep and longer time to fall asleep.
