A Food First Approach to More Common Micronutrient Deficiencies in Athletes

A frequent question Pierre and I receive is what vitamins and supplements we recommend for athletes. I think the expected response is a simple “Oh, iron is an absolute must, and X brand is the one to go for!” Unfortunately, however, there is no short answer, no quick fix, and no one-size-fits-all response to this question.

Every individual has unique nutrient requirements influenced by factors such as age, gender, genetic predispositions, medical history, dietary habits, physical activity levels, and overall lifestyle. These variables determine the body's specific nutritional needs for optimal health and performance.

That said, there are several micronutrient (vitamin and mineral) deficiencies for which athletes are at a higher risk. In some cases, an athlete may experience deficiency-related symptoms, but the only accurate means of diagnosis is through blood tests. If you think you have a critical deficiency, then the best approach is to see a physician and undergo the relevant testing protocols. If you’re interested in preventing or correcting mild micronutrient imbalances, whole foods and a balanced diet can be remarkably effective!

Let’s discuss a few of the more common vitamin and mineral deficiencies in athletes, as well as which foods offer the best natural sources of each.

Magnesium

Magnesium is the fourth most abundant mineral in the body and is involved in an extensive range of metabolic reactions. It helps maintain normal nerve and muscle function, heart rhythm, vasomotor tone (constriction and relaxation of blood vessels), blood pressure, immune system, bone integrity and blood glucose levels, and also promotes calcium absorption.

From an athletic point of view, the value of magnesium lies primarily in its role in energy production and storage, oxygen uptake, electrolyte balance and maintenance of blood glucose levels. The relationship between exercise and magnesium status is therefore well-researched, and there is evidence that even marginal magnesium deficiency impairs exercise performance.

As with most vitamins and minerals, however, a varied diet with sufficient energy covers the needs of most athletes. Natural sources of magnesium include legumes, nuts, grains, vegetables, milk and meats. Top sources in terms of concentration are pumpkin and chia seeds, almonds, spinach, cashews, peanuts and peanut butter, beans (black, Edamame, kidney), soya milk, potatoes, brown rice, bananas, salmon and fortified breakfast cereals.

*Note: according to a 2020 paper on the value of magnesium in reducing the incidence of muscle cramps (especially nighttime leg cramps), the consensus was that magnesium does not provide clinically relevant benefits.

Magnesium for skeletal muscle cramps (Review)

Zinc

Like magnesium, zinc is crucial for several biological functions. The first of these is catalytic, or chemical, reactions. Zinc serves as a cofactor for over three hundred enzymes in the human body, which drive processes like energy production, tissue repair, and muscle growth. Secondly, zinc plays a valuable role in cell structure and stability, meaning it contributes to tissue integrity. For athletes, this means zinc supports efficient metabolism and recovery after exercise, allows the body to repair and rebuild stronger, and also plays a protective role in muscles and joints during exercise. Our nervous, reproductive and immune systems are all affected by zinc levels, with the mineral’s relationship to the immune system being fairly complex. 

A detailed paper on Zinc and the immune system provides insight into the different ways in which zinc influences the immune system. In summary, the enzymes to zinc contributes influence various organ functions, which have a secondary effect on the immune system. Additionally, it’s role in cell structure and stability includes the production, maturation and function of leucocytes (white blood cells) which are core to the immune system.

Dietary intake and resorption of zinc depends on the composition of the diet and also one’s age and disease status. Studies have found that the body absorbs greater amounts of zinc in times of need, provided it is available through the diet. In general, animal proteins are rich in zinc, but its absorption can be impaired by phytic acid – a plant compound recognised as an antinutrient because of its interference with the absorption of certain minerals. 

Natural sources of zinc which can be consumed to increase one’s dietary intake include meat, fish, seafood, eggs and dairy products. Beans, nuts, and whole grains contain zinc, but the bioavailability is lower due to the phytates. Many modern breakfast cereals are fortified with zinc, and these therefore contribute a major source of zinc in the U.S. The amount of zinc absorbed from food ranges from 5% to more than 50%, with absorption from mixed meals (containing a combination of animal-based and plant-based foods) being lower than from meals containing only animal-based foods.

Calcium

98% of Calcium – the most abundant mineral in the body – is stored in our bones. This reservoir of calcium is used to maintain calcium homeostasis, and our bones undergo constant remodelling during growth, repair, and mineral redistribution. In addition to being the building blocks of bones and teeth, free calcium in the circulatory system, extracellular fluid and various tissues plays a role in muscle function, electrical stimulus of the heart, blood vessel contraction and dilation, blood clotting, nerve transmission and hormonal secretion. All of these, in particular optimal muscle and heart function, are important for endurance athletes.

While diet is not usually responsible for calcium deficiencies, it is becoming an increasing risk as non-dairy and vegetarian diets increase in popularity. There are seldom signs of early calcium deficiency, unless the cause is an underlying health issue or the use of certain medications. In the long term, however, chronic calcium deficiency can lead to extreme fatigue, muscle ache and cramping, osteopenia (low bone density), severe premenstrual syndrome (PMS), increased risk of depression, and a decline in mental health.

Milk, yogurt, and cheese are rich natural sources of calcium. Non-dairy sources include tofu, tinned sardines and salmon, as well as certain dark green leafy vegetables, such as kale, broccoli, and Chinese cabbage. Most grains do not have high amounts of calcium unless they are fortified, as some cereals are. As with zinc, calcium absorption varies with food type. Absorption from dairy products and fortified foods is about 30%, while plant compounds such as phytic and oxalic acid can decrease calcium absorption. For example, absorption of calcium from spinach is only 5%, versus about 27%, for milk. Bioavailability from broccoli, kale, and cabbage is better as they do not contain the abovementioned compounds. Net absorption of dietary calcium is also reduced to a small extent by the consumption of caffeine and phosphorus, and to a greater extent by a low status of vitamin D.

Vitamin D

Vitamin D is a fat-soluble (stored in fat tissue and the liver) vitamin found in two main forms, D2 and D3. Vitamin D3 (cholecalciferol) is formed in the skin after exposure to sunlight or UVB radiation and can also be obtained through dietary intake of animal meat, fish and eggs. Vitamin D2 (ergocalciferol) is synthesized in plants, also upon exposure to UVB, and can be obtained from certain plants and fungi (such as mushrooms) but in lower concentrations than its animal-derived equivalent.

The primary biological function of active vitamin D is to maintain serum calcium and phosphorus homeostasis, essential for bone mineralisation and neuromuscular function. Whether endogenous or exogenous, vitamin D3 undergoes hydroxylation first in the liver and then in the kidneys, where it forms calcitriol – its hormonally active form. Calcitriol increases the absorption of calcium from the intestines to help replenish serum calcium levels. If dietary calcium is insufficient, calcitriol stimulates osteoclasts (bone-resorbing cells) to break down bone tissue, releasing calcium into the bloodstream. Vitamin D’s role in the muscular system makes it important for overall mobility and strength, and it also contributes towards a healthy immune system.

While South Africans are not particularly high-risk cases for vitamin D deficiency, it is not unheard of, even amongst outdoor athletes. Factors that increase the chances of a vitamin D deficiency include pigmented skin, ageing (the skin produces less vitamin D as one grows older) and low sunshine exposure. Direct sun exposure on unprotected skin is required for vitamin D formation, but it is important to avoid excessive or prolonged exposure. In general, 10-30 minutes several times a week is recommended, bearing in mind that lighter skin tones require less time, and that UVB is stronger during the summer months, between 10am and 2pm.

Incorporating vitamin D-rich foods into the diet can reduce the required sun exposure, although few foods naturally contain vitamin D. The flesh of fatty fish (trout, salmon, tuna, and mackerel) and fish liver oils are among the best sources, with beef liver, egg yolks, and cheese also having small amounts of vitamin D3. Vegetarians and vegans will need to look harder, but mushrooms do provide variable amounts of vitamin D2, and certain cereals and milks (animal and plant-based) are fortified with vitamin D3 (particularly in the U.S.).

Interesting reading: This study found that higher vitamin D intake predicted significantly lower risk of stress fracture, while calcium intake was unrelated. 

Vitamin D, Calcium, and Dairy Intakes and Stress Fractures Among Female Adolescents

B Vitamins

In contrast to the fat-soluble vitamin D, the B vitamins (and vitamin C) are water soluble. This class of vitamins is not stored in the body and must therefore be consumed regularly. They are also excreted through bodily fluids such as urine and sweat, which means athletes may lose more than the average sedentary person. But the good news is that a well-rounded nutrition plan and varied diet should meet the requirements of even endurance athletes, without the need for supplementation. Deficiencies are generally rare, with alcohol abuse, low caloric intake and older age (reduced absorption, dietary changes, medications) being increased risk factors.

There are eight B vitamins, described as follows: thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7), folate (B9) and cobalamin (B12). B vitamins act as coenzymes, making them critical to many processes, particularly energy pathways. They are also important for normal appetite, good vision, healthy skin, healthy nervous system, and red blood cell formation.

With the exception of B12, the B vitamins are typically synthesised by plants and consumed by animals. They can therefore be found in both plant and animal sources, except for vitamin B12 which is synthesized exclusively by microorganisms of animal or soil origin and only enters the human food chain through animal-derived products. For this reason, vegans are at a higher risk for B12 deficiency.

Several food groups which provide the highest concentrations of B vitamins in general include meat, fish, poultry, eggs, dairy products, whole grains, legumes, green leafy vegetables, potatoes, bananas, nuts and seeds.

TABLE 1: Individual Vitamin B Functions and Sources (Click image to enlarge)

It is worth noting that, according to the Colorado State University, large amounts of vitamin B-complex supplements and multivitamins are not recommended. Excesses of these vitamins have no known benefit, and while a surplus of water-soluble vitamins is normally excreted through the urine, there may be increased risk of GIT disturbances and urinary calculi (vitamin C toxicity) or liver damage, changes in vision, headache, itchy skin, and hair loss (vitamin A toxicity).

Intravenous vitamin therapy (IVVT) offers itself as a great topic for debate, with most of the “menu” options including a vitamin B complex and vitamin C. While there are a lot of opinions, non-scientific articles and blogs available on the topic, there is very little evidence-based research for the validity of routine, wellness-oriented usage of IVVT. This in itself is somewhat concerning.

I leave you with the opinions of a South African doctor - “pissing money [vitamins?] into the wind,”  the Australian Dr Chelsie McMullin - “The fact you’ve had the volume of fluid quickly will make you feel a little bit better temporarily, but that’s an expensive [cure], and you’ll likely have the same result if you drink a few electrolytes,” and the best scientific article I could find: Consumer Intravenous Vitamin Therapy: Wellness Boost or Toxicity Threat

Iron 

Iron is a mineral that plays a critical role in the body, primarily in the formation of haemoglobin, a protein of red blood cells that transports oxygen from the lungs to tissues. Iron is also involved in producing myoglobin, which stores oxygen in muscle tissues for use during muscular activity. Iron supports muscle metabolism, healthy connective tissue, physical growth, neurological development, cellular functioning, and synthesis of certain hormones.

Dietary iron has two main forms: heme and nonheme. Plants and iron-fortified foods contain nonheme iron only, whereas meat, seafood, and poultry contain both heme and nonheme iron. Heme iron has higher bioavailability than nonheme iron. Vitamin C enhances the bioavailability of nonheme iron, and interestingly, heme sources (meat, seafood, poultry) also increase nonheme iron absorption. This is in contrast to plant sources, containing phytates and polyphenols, which decrease nonheme iron absorption. Beverages such as tea, coffee, red wine and cocoa high in polyphenols. Calcium has also been shown to have an inhibitory effect on iron absorption, both heme and nonheme.

Common risk factors for iron deficiency include being female, especially with heavy menstrual bleeding, being a frequent blood donor, having a GIT disorder or prior GIT surgery, and chronic inflammation (associated with conditions such as rheumatoid arthritis). Exercise, primarily high-intensity and endurance training, is also considered a risk factor for depletion of iron stores*. Potential reasons include increased iron requirements, elevated iron loss, foot strike haemolysis, sweat loss, reduced blood to the gut during exercise leading to gastrointestinal iron loss, haematuria (blood loss in the urine through trauma to the bladder wall), and exercise-induced inflammation which can elevate hepcidin levels (a hormone that decreases iron absorption). While several of these factors are extreme rather than every-day occurrences, it warrants paying extra attention to your iron intake as an athlete.  

Natural sources of animal-origin iron include oysters, mussels, beef, lamb, sardines, tuna, salmon, chicken, turkey, pork and eggs. Plant-based sources include fortified breakfast cereals, white beans, soybeans, red kidney beans, lentils, tofu, dark chocolate (45-70% cacao solids), chickpeas, potato, cashews, pistachios, walnuts, pecans, green peas, broccoli, spinach and raisins.

It is worth noting that iron overload or iron toxicity can also occur, and it is therefore not recommended to combine oral iron supplements and excessive amounts of iron-rich foods for prolonged periods without the advice of a medical practitioner.

*The IRONy in Athletic Performance

In conclusion, addressing and avoiding potential micronutrient deficiencies through a food first approach should be top priority for every athlete. Whole foods not only provide essential vitamins and minerals but also offer synergistic benefits that supplements alone may lack. Athletes who consume high-quality meals encompassing a diverse range of wholefoods can enhance their recovery, energy levels, and immunity, and reduce the risk of deficiencies which could hinder performance. While supplementation may occasionally be necessary, it should complement—not replace—the foundation of a balanced, nutrient-rich diet. 

More about the author:

Nicolette is not only a top ultra trail runner, but also a certified coach and nutritionist. Her personal journey with nutrition has led her to research and, in turn, share what she knows about how to fuel in a holistic manner with the athletes she works with..

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