Vitamin & Mineral Supplements

Iron, vitamin D, magnesium, calcium, and the B vitamins are the micronutrients most commonly deficient or depleted in endurance athletes, according to a review published in the International Journal of Sport Nutrition and Exercise Metabolism. Iron supports oxygen transport and is depleted through foot-strike hemolysis, sweat, and gastrointestinal bleeding during intense exercise. Vitamin D regulates bone health and immune function, and deficiency is common in athletes who train indoors or live at higher latitudes. Magnesium supports over 300 enzymatic reactions including muscle contraction and energy metabolism, and is lost through sweat at measurable rates.

The International Olympic Committee position is that athletes with a well-planned, energy-sufficient diet may not need a multivitamin. However, many athletes, particularly those restricting calories, following elimination diets, or training at very high volumes, fail to meet micronutrient needs through food alone. A study published in the journal Nutrients found that a significant proportion of endurance athletes fall below recommended intakes for at least one micronutrient. Blood testing is the most reliable way to determine whether supplementation is warranted. A targeted approach based on identified deficiencies is more effective and more cost-efficient than a broad-spectrum multivitamin taken without diagnostic information.

Yes. Fat-soluble vitamins A, D, E, and K accumulate in body tissues and can reach toxic levels with prolonged high-dose supplementation. Water-soluble vitamins are generally excreted when consumed in excess, though very high doses of vitamin B6 can cause peripheral neuropathy. Mineral toxicity is also possible, particularly with iron and zinc, both of which interfere with copper absorption at elevated doses. The National Academy of Medicine (formerly the Institute of Medicine) publishes tolerable upper intake levels for each micronutrient, which serve as the ceiling for safe supplementation. More is not better, and exceeding these limits carries documented health risks.

Blood testing through a physician or sports medicine specialist is the definitive method. Common panels for endurance athletes include serum ferritin and iron studies, 25-hydroxyvitamin D, serum magnesium, and a complete blood count. Symptoms alone are unreliable because fatigue, weakness, and impaired performance, the most common complaints, overlap across multiple deficiencies and non-nutritional causes. Regular testing during high-volume training blocks, typically two to three times per year, provides a longitudinal picture of your micronutrient status and allows supplementation to be adjusted based on objective data rather than guesswork.

Yes. Sweat contains measurable amounts of sodium, potassium, calcium, magnesium, zinc, iron, and trace minerals. A study published in the International Journal of Sport Nutrition and Exercise Metabolism measured significant mineral losses in athletes exercising in warm conditions. Sodium losses are the most substantial, ranging from 300 to over 1,000 milligrams per liter of sweat. Mineral losses through sweat compound dietary insufficiency in athletes who are already consuming less than recommended amounts. The cumulative effect over weeks and months of heavy training can produce subclinical deficiencies that impair performance and recovery before obvious symptoms appear.

Fat-soluble vitamins A, D, E, and K absorb best when taken with a meal containing fat. Iron absorbs best on an empty stomach, taken with vitamin C and separated from calcium, coffee, and tea by at least two hours. However, iron on an empty stomach causes nausea or cramping for many people — if that applies to you, taking it with a small amount of food (avoiding dairy or calcium-rich foods) is an acceptable tradeoff for consistency. Magnesium is commonly taken before bed because of its role in supporting sleep quality and muscle relaxation. B vitamins are best taken in the morning because they support energy metabolism and can interfere with sleep if taken late. Zinc should be taken with food to reduce nausea but separated from iron and calcium to prevent absorption competition. Timing matters more for some nutrients than others, but consistency is the most important factor.

Liquid vitamins bypass the dissolution step required for tablets, which means they become available for absorption more quickly. This is an advantage for individuals with compromised digestive function or those who have difficulty swallowing pills. For most healthy athletes, quality tablets and capsules dissolve and absorb efficiently. That said, the chemical form of the nutrient matters more than the delivery format — magnesium citrate, for example, absorbs significantly better than magnesium oxide regardless of whether it comes in a capsule or liquid. One meaningful exception is liposomal delivery, which encapsulates nutrients in phospholipid vesicles to enhance absorption independent of digestive function. This is a genuine advantage for nutrients like glutathione, vitamin C, and CoQ10 that are otherwise poorly absorbed in standard forms. Choose the format that addresses your specific needs and that you will take consistently.