Calcium for bone health: a quick guide for athletes

Calcium is the main mineral your body uses to build and maintain bone. Adolescence is the single most important window for building bone mass — getting enough calcium during those years has a lasting effect on bone strength for life, which is part of why it matters so much for young athletes, and part of what’s at stake in conditions like RED-S.

Good food sources

Milk, yogurt, and cheese are the most concentrated sources, but calcium also shows up in sesame seeds and almonds, leafy greens like spinach, and calcium-fortified foods — many soy products, cereals, fruit juices, and plant-based milk substitutes have it added.

If you use a supplement

A few practical details make a real difference to how much you actually absorb:

• Split it up. Your body can only absorb about 500 mg at a time, so spreading intake across the day works better than one large dose.
• Take most forms with food. Calcium carbonate (a common, inexpensive form) absorbs best with a meal; calcium citrate is gentler on the stomach and absorbs well with or without food.
• Pair it with vitamin D — your body needs vitamin D to actually absorb the calcium you take in, though they don’t need to be taken at the exact same moment. See our vitamin D guide.
• Watch what blocks absorption. Caffeine and alcohol reduce calcium absorption, and if you’re low on iron, zinc, or magnesium, it’s worth taking your calcium supplement at a different time from those, since calcium competes with them for absorption. See our supplements guide for more on quality and safety.

How much do you need?

Requirements rise sharply in the teenage years: roughly 1,300 mg/day for ages 9–18, dropping to about 1,000 mg/day for most adults, and rising again after 50. These are general population guidelines; an athlete with RED-S risk factors or a history of stress fractures may be advised to aim higher — that’s worth discussing with a clinician or dietitian rather than guessing.

This page is educational and general in nature and does not replace individualized nutrition advice — see our medical disclaimer.