BoneScience Research Notes · Last reviewed: 2026-10 · General information, not medical advice
- Kids build about 39% of their adult bone mineral in just four years, around the growth spurt.
- The two habits with the best evidence for strong bones are active play and enough calcium-rich food.
- Jumping, running and ball games help most, especially before puberty.
Bones are still being built
Bone is living tissue. During childhood and the teen years, the body keeps adding minerals to it. Minerals are what make bone hard and strong.
At some point, that adding slows down and stops. The most bone a person ever has is called peak bone mass. After that, the body slowly starts to lose bone over many decades.
So the bone a child builds now is the bone they carry into adult life.
The four-year window
A Canadian team scanned the same children's bones again and again, from childhood into their late twenties. They lined everyone up by their growth spurt, not by birthday. The growth spurt is the fast-growing stretch during puberty.
In the four years around the fastest growth, two before and two after, kids built about 39% of their adult total-body bone mineral. That is a lot of bone in a short time.
Total-body bone mineral leveled off around age 18 in girls and 20 in boys. By the late teens to the late twenties, peak bone mass was reached, depending on the part of the body.
When does the window open?
It depends on when your child's growth spurt comes. Girls usually hit their fastest growth about two years before boys. In a classic study, boys peaked at about 14 on average.
A drawing of the typical timing, not real data. Every child's timing is different.
So the window often opens around age 10 in girls and around 12 in boys, give or take a couple of years. Your child's own growth chart is the best clue.
What helps: the two best-supported habits
In 2016, the National Osteoporosis Foundation reviewed the research since 2000 on bones in kids and teens. It graded each factor by how strong the evidence was.
Only two got the top grade: enough calcium in the diet, and physical activity. The review said lifestyle shapes about 20 to 40% of adult peak bone mass. Good evidence also supported vitamin D and dairy foods.
Which kind of activity?
Not all exercise loads bone the same way. Bones respond to impact, when the body has to carry its own weight.
A 2014 review pooled 27 studies of programs like jumping and running in kids. These programs raised bone mineral and bone density. The gains were small on average. They were bigger in kids who had not started puberty yet and who ate more calcium.
What about lifting weights? A Canadian expert group said strength training can be fairly safe for kids when it is done right. That means a qualified coach, good form, light to moderate loads, and 2 to 3 sessions a week with rest days in between.
What this research says / doesn't say
Says: About 39% of adult bone mineral is built in the four years around the growth spurt. Calcium intake and physical activity have the best evidence for building strong bones. Jumping and running help, especially before puberty.
Doesn't say: That any habit changes how tall a child will be. Bone mineral is about bone strength, not height. The exercise effects were small on average, and the bone study followed one group of Canadian kids.
Three things to try this week
- Add impact play. Jump rope, tag, basketball, soccer or dance all have kids carry their own weight.
- Build calcium into meals. Milk, yogurt, cheese, fortified soy milk or tofu made with calcium.
- Keep it going through the spurt. The growth spurt years are when bone builds fastest. Help your child find an activity they enjoy and want to keep doing.
Sources
- Baxter-Jones AD, Faulkner RA, Forwood MR, Mirwald RL, Bailey DA. Bone mineral accrual from 8 to 30 years of age: an estimation of peak bone mass. J Bone Miner Res. 2011;26(8):1729-1739. doi:10.1002/jbmr.412
- Weaver CM, et al. The National Osteoporosis Foundation's position statement on peak bone mass development and lifestyle factors: a systematic review and implementation recommendations. Osteoporos Int. 2016;27(4):1281-1386. doi:10.1007/s00198-015-3440-3
- Behringer M, Gruetzner S, McCourt M, Mester J. Effects of weight-bearing activities on bone mineral content and density in children and adolescents: a meta-analysis. J Bone Miner Res. 2014;29(2):467-478. doi:10.1002/jbmr.2036
- Behm DG, Faigenbaum AD, Falk B, Klentrou P. Canadian Society for Exercise Physiology position paper: resistance training in children and adolescents. Appl Physiol Nutr Metab. 2008;33(3):547-561. doi:10.1139/H08-020
- Marshall WA, Tanner JM. Variations in the pattern of pubertal changes in boys. Arch Dis Child. 1970;45(239):13-23. doi:10.1136/adc.45.239.13
This article is general information, not medical advice. If you have questions about your child's bone health, talk with your pediatrician.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
BoneScience makes Dr's Grow UP, an AM/PM daily nutrition system for ages 10+, NSF Certified for Sport®.
The studies above were not conducted on BoneScience products.
BoneScience makes free tools for parents: Growth Calculator · Growth Coach
