Boning Up on Calcium for the Young Swimmer
By Jill Castle, MS, RDN
Calcium is an important part of every child and teen’s diet. When one hears about getting enough calcium in the diet, thoughts of milk mustaches and old women with osteoporosis float through the mind. For most athletes, there is a natural advantage to bone health because exercise helps to build and sustain bone. Not necessarily the case with the swimmer.
Calcium has two major roles: bone mineralization (making the bones hard and dense) and normal muscle contraction. There is one golden opportunity for building bone and optimize bone health and that occurs in the first two decades of life. After that, the body has completed bone building and shifts to the task of maintaining bone density. When adequate calcium is consumed throughout the adult years, bone density is likely to stay intact and the body will receive adequate amounts of calcium for other normal functions such as rhythmic muscle contractions (think regular heart beat). However, when calcium is short in the diet, a calcium withdrawal is made from the bone. This removal system keeps calcium at a steady level throughout the body. The bottom line: calcium balance and turnover is ongoing, with bone stores of calcium being called upon when calcium is low in the diet.
Fortunately, building bone and bone health does not rest upon getting adequate calcium alone (although this is a very important element). Weight-bearing exercise (high-impact or odd-impact loading activities) and other nutrients such as vitamin D, potassium and magnesium, are important to bone health too.
Unfortunately, young swimmers are swimming against the current when it comes to bone health. Swimming is a non-impact sport, and according to a literature review in 2011 by Tenforde et al, is not associated with improvements in bone health. This makes optimal calcium intake, as well as the consumption of other important bone nutrients, and participation in other impact-loading exercises, more critical to healthy bone formation.
To complicate matters more, children and teens are not meeting their calcium requirements, according to the 2010 Dietary Guidelines for Americans (DGA). During the period of childhood and adolescence (ages 9-18 years), the needs for calcium are at their highest in life, a level of 1300 milligrams per day. Yet, kids and teens in general don’t meet this requirement, with only 15% of girls and 22% of boys aged 9-13 years and 10% and 42% of 14-19 year old girls and boys, respectively, meeting or exceeding this level.
Consuming enough calcium is an important goal for all young athletes—and it’s easy to do! Below are some of the top food sources of calcium. Do the math: a bowl of calcium-fortified cereal with milk and a glass of OJ may cover most, if not all, a swimmer’s calcium needs for the day.
Selected sources of calcium (mg) include:
- Ready-to-eat cereals, calcium fortified: 100 – 1,000 mg per ½ cup
- Orange juice, calcium fortified: 500 mg per 1 cup
- Soy beverage, calcium fortified: 80 – 500 mg per ½ cup
- Plain non-fat yogurt: 452 mg per 1 cup
- Romano cheese: 452 mg per 1 ½ ounce
- Low fat fruited yogurt: 338 – 384 mg per 1 cup
- Mozzarella cheese: 333 mg per 1½ ounces
- Low fat milk: 305 mg per 1 cup
- Low fat chocolate milk: 290 mg per 1 cup
- Soft serve vanilla frozen yogurt: 105 mg per 1 cup
More calcium resources are located in the National Nutrient Database for Standard References (www.ndb.nal.usda.gov) and in my book, Fearless Feeding.
Jill Castle, MS, RDN is a registered dietitian/nutritionist and childhood nutrition expert. She is the co-author of Fearless Feeding: How to Raise Healthy Eaters from High Chair to High School and creator of "Just The Right Byte," a childhood nutrition blog. She lives with her husband and four children in New Canaan, Conn. Questions? Contact Jill at Jill@JillCastle.com.