Iron and calcium influence each other's absorption in the intestines – calcium can inhibit iron absorption if both nutrients are taken simultaneously. Therefore, it is advisable for athletes to pay attention to the correct timing of supplementation.
Interaction during absorption
Calcium can impair the absorption of iron (especially plant-based non-heme iron) when both nutrients are consumed together. Studies show that doses of 300-600 mg of calcium can reduce iron absorption. This is particularly relevant for dietary supplements, less so for a varied mixed diet.
Recommendations for athletes
Athletes have an increased need for both iron and calcium – iron is important for oxygen transport and endurance performance, calcium for bones and muscles. If a deficiency is proven, targeted supplementation can be useful, but should be done under professional supervision. To maximize absorption, a time interval between iron and calcium supplements is recommended, for example, at least two hours.
Practical advice on supplementation
- Iron supplements should preferably be taken on an empty stomach or with foods containing vitamin C, as vitamin C increases absorption.
- Take calcium supplements separately from iron-containing products, preferably with a sufficient time interval.
- Pay attention to high dosage/avoid overdose: Too high amounts of supplements can cause side effects or overdose.
- Female athletes and endurance athletes should have their iron levels checked regularly and only supplement if a deficiency is proven.
- In addition, be aware that caffeine inhibits the absorption of iron.
Other relevant interactions
- Other minerals such as magnesium and zinc also compete with iron and calcium during absorption.
- Phytates and polyphenols from plant-based foods can additionally inhibit both iron and calcium absorption.
- Caffeine inhibits iron absorption.
Overall, when supplementing, an intake plan tailored to individual needs is important, especially for athletes with increased needs or dietary restrictions such as vegetarians/vegans.
Sources
Calcium - Interactions https://www.vitalstoff-lexikon.de/Mineralstoffe/Calcium/Interaktionen
Athletes are often undernourished https://www.eisen-netzwerk.de/risikogruppen/sportler
Micronutrients in Sports | Blog https://www.burgerstein-foundation.ch/de-DE/wissen/blog/wann-sind-nahrungsergaenzungsmittel-im-sport-sinnvoll
Iron - Interactions https://www.vitalstoff-lexikon.de/Spurenelemente/Eisen/Interaktionen
How micronutrient deficiencies affect athletic performance ... - Medicross https://www.medicross.com/blog/ernaehrung/mikronaehrstoffdefizite-und-sportliche-leistung/
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