The Bone Bank Is 90% Full by 17: What Every Parent Should Know About Teen Calcium

Here is a question most parents have never been asked: does your teen get the calcium in four cups of milk, every single day? If the answer is "probably not", you are in good company, and the reason it matters comes with a timeline.

Short answer: Teens aged 9 to 18 need 1,300 mg of calcium a day, more than any other age group, because these are the years the skeleton is built. Food should supply most of it. If your teen also takes an iron-containing supplement, take calcium and iron at different times of day, because calcium taken together with iron reduces how much iron the body absorbs.

The bone bank is 90% full by 17

By the time the teenage growth spurt ends, most of the bone a person will ever have is already in place. The U.S. National Institutes of Health notes that about 90% of adult bone mass is built by around age 17. A systematic review on peak bone mass reached a practical conclusion: what children and teens eat, and how active they are, shapes the bone they carry into adulthood.

Picture it
Think of bone as a savings account.The growing years are when the deposits happen. By around age 17, about 90% of the account is filled. After the late twenties, the body starts slowly drawing it down for the rest of life. The bigger the balance at the top, the more there is to draw from later.
Birth~17: about 90% depositedLater life
Osteoporosis International · 2016Systematic reviewNational Osteoporosis Foundation position statementDiet and physical activity in childhood and adolescence shape peak bone mass.doi:10.1007/s00198-015-3440-3 ↗ NIH · Office of Dietary Supplements1,300 mgrecommended per day, ages 9–18The highest calcium recommendation of any age group.ods.od.nih.gov ↗
A teen soccer player running at sunset
Training, school and a growing skeleton all draw on the same daily nutrients.

What 1,300 mg looks like on a plate

Picture it
1,300 mg is roughly the calcium in four cups of milk.Every day, from age 9 to 18. Yogurt, cheese, fortified soy milk and calcium-set tofu can stand in for some of those cups.

Most of a teen's calcium should come from food. The richest everyday sources are dairy, calcium-fortified soy milk and juices, canned fish eaten with the soft bones, and tofu made with calcium. Several servings a day are usually needed, which is exactly where busy schedules, skipped breakfasts and picky eating get in the way.

The timing problem most families miss

Calcium and iron compete. In a classic study of 126 people, adding 300 to 600 mg of calcium to a meal reduced iron absorption by 50 to 60%. For active teens, especially girls who have started their periods, iron matters too.

Iron absorbed, no added calcium100%
With 300–600 mg calcium40–50%

Iron absorbed relative to the same meal without added calcium (Hallberg et al., 1991).

Am J Clin Nutr · 1991126people studied300–600 mg of calcium with a meal reduced iron absorption by 50–60%.doi:10.1093/ajcn/53.1.112 ↗
Picture it
Iron and calcium are two people trying to get through one door.Send them together and one gets held back. Send iron in the morning and calcium at night, and both get through.
☀️ Morning
Iron
🚪
🌙 Night
Calcium
Time Better paired with Keep apart from
Morning Iron-rich foods, vitamin C Large calcium doses
Evening Calcium, magnesium, vitamin K2 Iron supplements

This is the reason Dr's Grow UP is split into two formulas: iron and zinc in the morning, calcium and magnesium at night.

Dr's Grow UP AM and PM
Dr's Grow UP — AM + PMIron in the morning, Albion® calcium and magnesium at night. NSF Certified for Sport®. It adds to the plate; it does not replace it.
See what's inside

Questions parents ask

Can my teen get enough calcium from food alone?
Often, yes, with several dairy or fortified servings every day. A supplement only fills the gap that remains.
Is more calcium always better?
No. There is an upper limit for every age group. Count food and supplements together, and ask your doctor if you are unsure.
Does vitamin D matter here?
Yes. Vitamin D helps the body absorb calcium, which is why it is usually paired with calcium in bone-focused formulas.

Next in Growing Years Science: How we check every number on our label · 8 important nutrients for bone density

  1. NIH Office of Dietary Supplements. Calcium — Health Professional Fact Sheet.
  2. NICHD, U.S. National Institutes of Health. Osteoporosis prevention begins in childhood.
  3. 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. doi:10.1007/s00198-015-3440-3
  4. Hallberg L, et al. Calcium: effect of different amounts on nonheme- and heme-iron absorption in humans. Am J Clin Nutr. 1991;53(1):112-9. doi:10.1093/ajcn/53.1.112

*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. This article is for general education and is not medical advice.

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