Calcium

Calcium is a mineral that builds and maintains bone and helps regulate muscle contraction and nerve function.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.} Bones gain length and density during adolescence, with up to 90% of peak bone mineral density reached in late adolescence.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.} In adults, calcium helps maintain that density.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.} When intake falls short, the body draws calcium from bone to keep blood and muscle levels steady.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.} Deficiency can limit peak bone density and raise fracture risk later in life.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.}

The IPTA textbook lists a recommended dietary allowance (RDA) of 1,000 mg a day for most adults, 1,300 mg for teenagers and 1,200 mg for people over 50, with an upper limit of 2,500 mg a day for ages 19 to 50.^{2International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 523.}

In practice

• In US survey data cited by the NSCA, just 15% of girls aged 9 to 13 and under 10% of females aged 14 to 18 met the adequate intake from diet alone.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.}
• The NSCA recommends dairy products and other calcium-rich foods for athletes, with supplements suggested by a doctor or registered dietitian if diet can’t cover the need.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.}
• Calcium can interfere with nonheme iron absorption, which matters when a client is also working on iron intake.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 211.}
• Absorption falls with age, so the IPTA textbook pairs vitamin D with calcium for bone health.^{2International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 523.} USA Triathlon advises a diet rich in calcium, iron and vitamin D, and links stress fractures to inadequate nutrition.^{3USA Triathlon, Complete Triathlon Guide, p. 41.}
• Refer clients with nutrition deficiencies or chronic conditions requiring specific diets to a dietitian and physician; prescribing supplements is outside a trainer’s scope of practice.^{4International Sports Sciences Association, Fast Track Study Guide: Nutrition, p. 1.}