The Short Scoop on Supplements – Part II

The Short Scoop on Supplements – Part II

In the last article, I covered the types of supplements available and listed some important questions you should ask yourself when making a decision on whether to start a supplement or how to choose supplements that are safe and cost-effective.  In this article, let us take a look at a few common supplements that many athletes inquire about or take on a regular basis without knowing their purpose.

1. Magnesium

This is an important mineral and electrolyte for athletes. Magnesium has many roles, including bone metabolism, immune system health, muscle contraction, and carbohydrate and fat metabolism. It is not common to have magnesium levels tested as part of routine blood work unless we work with a functional medicine doctor or specifically request this lab to be drawn. However, it has been suggested that the majority of us are deficient in this micronutrient. Two common reasons for deficiency are that there is simply an inadequate intake of its food sources, and secondly, the soils in which the foods are grown are lacking in the mineral.  I do not recommend supplementing without first having a dietary assessment done by a dietitian who also considers your physical activity levels.  A dietitian will know the right dosage for you, the best absorbable forms, and can give you further guidance on nutrition to optimize your magnesium intake. Note that good food sources of magnesium include dark leafy greens, pumpkin and sunflower seeds, brazil nuts, almonds, beans, and whole grains.

2. Vitamin D

Commonly known as the “sunshine vitamin”, the process to synthesize vitamin D in the body is quite complex. Its roles in the body are numerous but most notably for bone health and chronic disease prevention.  Many of you assume that because you live in a sunny area and spend time outdoors, you are getting adequate sun exposure.  Or, if you consume fatty fish, cod liver oil, or fortified foods such as cow’s milk or cereals, there should be no deficiency. This is not necessarily the case.  Obviously your sun exposure varies with the seasons, but even in the summer months, I find that athletes have a suboptimal level of vitamin D. I suggest you have vitamin D  (the active form, 1,25-dihydroxyvitamin D3) checked at least once per year along with other blood work. Be aware that the range for what is considered “normal” does not apply to endurance athletes.  The acceptable value is often 30 ng/mL or higher, but I recommend a value between 50-80 ng/mL.  Note that a deficiency or suboptimal level can negatively affect athletic performance in terms of injury risk, muscle fatigue, and illness. Supplementation can be in the range of 1000-5000 IU daily or weekly, but should be reviewed by a sports-minded physician or sport dietitian to determine the proper dosage.

3. Iron

Another important mineral for athletes is iron, which carries oxygen to the body’s tissues and has roles in energy metabolism. There are different stages of iron deficiency that can occur (with the most severe form being anemia), but it tends to be more common in endurance athletes following strict plant-based diets or female pre-menopausal endurance athletes due to blood losses during menstruation, destruction of red blood cells in long-distance running (from the feet pounding), and inadequate intake of iron.  If you think you might be deficient in iron, I strongly suggest you first have your iron stores checked before supplementing as there is also the risk of iron overload, which has a host of harmful health implications.  Ask your doctor to run a“full iron panel”, which should include serum iron, ferritin, and total iron binding capacity labs.  Bonus points if you can get hepcidin checked. If you are an endurance athlete, I recommend you have your iron stores checked at least once per year (and in the base training cycle is ideal) and then review the results with a sports medicine doctor or your sport dietitian.  To get your food intake of iron, there are a variety of sources:  liver, beef, oysters, dark leafy greens, beans, broccoli, apricots, dates, almonds, and oats.

If you have any questions or concerns about these supplements, don’t hesitate to contact me at

Thank you!

Dina Griffin, MS, RD, CSSD, METS
Board Certified Sport Dietitian
Metabolic Efficiency Training Specialist

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