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Testosterone, Iron, and Thyroid Hormone Depletion in Cyclists

The Impact of Testosterone, Iron, and Thyroid Hormone Depletion on Cyclists: Causes, Symptoms, and Prevention Tips

The body is the essential tool to a cyclist or endurance athlete, and they take pride in working to keep in top working order. Cycling and endurance sports take a lot of work. Athletes are willing to push themselves to be their best. However, these activities can also harm the body in ways that many athletes are unaware of.  


In particular, testosterone depletion, iron depletion, and thyroid hormone depletion are common issues that cyclists and endurance athletes unwittingly face.


Testosterone, iron, and thyroid hormone are three critical elements of our health and well-being that can be depleted by intense training, leading to a range of symptoms and consequences.


To prevent deficits from impacting your fitness and harming your health, exploring and understanding the effects of cycling and endurance training on these elements, the signs of depletion, and strategies to prevent or mitigate their depletion are essential.

Testosterone, Iron, and Thyroid Hormone Depletion in Cyclists
Photo courtesy of TLBVelo @

Testosterone Depletion in Cyclists and Endurance Athletes

Testosterone is a hormone produced primarily in the testes (in men) and ovaries (in women). It plays a crucial role in building and maintaining muscle mass, bone density, red blood cell production, and regulating sex drive and mood. 


However, intense endurance training can lead to a decrease in testosterone levels, particularly in men. It is due to several factors, including increased cortisol (a stress hormone) levels, oxidative stress, and inflammation.


A research study published in Sports Medicine suggests that endurance training significantly affects the male reproductive system. At rest, testosterone appears lower in endurance-trained males than untrained males, potentially disrupting reproduction and performance. The scientists attributed the findings to a disturbance of the testosterone regulatory pathway.


Another study published in Hormones reveals that the longer an endurance athlete is engaged in consistent and chronic training, the lower their resting testosterone. The results suggest a reduction in resting testosterone plateaus at approximately 30 percent after five years of endurance training.

Causes of Testosterone Depletion in Cyclists

Endurance exercise causes acute elevations of the stress hormone cortisol more than strength and power training. Over time, repeated bouts of intense, long-duration training lead to adrenal gland enlargement due to high cortisol output.


The optimal metabolic function requires cortisol. However, continuous high levels of training stress can lead to chronic elevations that hinder the stress response, often resulting in low testosterone levels in endurance athletes.

Testosterone, Iron, and Thyroid Hormone Depletion in Cyclists underfueling imagage

When there is too much cortisol in the body, it can break down muscle tissue and cause persistent inflammation. Additionally, high cortisol levels can weaken the immune system, which may be why endurance athletes often get sick when undergoing intense, high-volume training.

Symptoms and Consequences of Testosterone Depletion in Cyclists

The symptoms of low testosterone can include decreased muscle mass and strength, fatigue, decreased libido, irritability, depression, and poor recovery from workouts. In addition, low testosterone levels can increase the risk of osteoporosis, cardiovascular disease, and metabolic disorders such as insulin resistance and type 2 diabetes.

Tips to Mitigate Testosterone Depletion in Cyclists

To prevent or mitigate testosterone depletion, cyclists and endurance athletes can take several steps:


Incorporate strength training into your workouts: Dial back your endurance work and add a few strength sessions. It will decrease the stress of endurance training, and studies suggest strength training increases testosterone.


Get enough sleep: Sleep deprivation can increase cortisone and lead to lower testosterone levels.


Eat a balanced diet: Prioritize a well-balanced nutrition plan with sufficient protein, healthy fats, and micronutrients such as zinc and vitamin D, essential for testosterone production.


Drink less alcohol: Heavy alcohol consumption reduces testosterone production.

Decrease stress: It goes without saying.

a group of cyclists in colorful jerseys

Iron Depletion in Cyclists and Endurance Athletes

Iron is an essential mineral that is crucial in many bodily functions. When the body’s iron stores run down, iron depletion occurs. Iron is vital for producing hemoglobin, which carries oxygen to the body’s tissues. An athlete may become anemic if the body cannot produce enough hemoglobin due to a lack of iron. 


A study published in the International Journal of Sport Nutrition and Exercise Metabolism found that iron depletion is prevalent among top-level athletes. The study found that 22% of participants had iron depletion.

An additional study published in Medicine and Science in Sports and Exercise evaluated the prevalence of iron deficiency and its impact on performance in female intercollegiate athletes. The study found that 31% of athletes had iron deficiency.

Causes of Iron Depletion in Cyclists

There are several causes of iron depletion in cyclists and endurance athletes. One of the leading causes is the increased demand for oxygen during exercise. 


The increased need can lead to an increase in the breakdown of red blood cells containing iron. In addition, training stimulates red blood cell production. Growth requires iron for the production of new tissues and blood cells.


Another cause of iron depletion is inadequate dietary intake of iron. Endurance athletes require more iron than sedentary individuals due to the increased demand for oxygen during exercise. If an athlete’s diet does not provide enough iron, they may become iron deficient. Vegetarians are at high risk. Low energy intake and extreme dieting behaviors exacerbate the condition.

Testosterone, Iron, and Thyroid Hormone Depletion in Cyclists low energy availability image

Endurance training also produces elevated levels of the hormone hepcidin. Research shows that hepcidin partially blocks absorption for up to six hours after exercise. Training-induced inflammation promotes hepcidin production leading to decreased iron.


Researchers also suggested that athletes lose iron through sweat, during menstruation, in the gastrointestinal tract during endurance training.

Symptoms and Consequences of Iron Depletion in Cyclists

Iron depletion can have several adverse effects on an athlete’s performance. One of the most common effects is fatigue. The body’s cells require iron for energy production. 


When iron stores are low, the body cannot produce enough energy, leading to fatigue. You won’t be able to train as hard as usual, and your body won’t respond or recover normally.


Iron depletion can also lead to a decrease in endurance performance. Hemoglobin carries oxygen to our muscles and needs iron for production. When there isn’t enough hemoglobin, the body’s tissues do not receive enough oxygen, and a decreased endurance performance results.


The symptoms of iron depletion may also include weakness, decreased appetite, pale skin, shortness of breath, and increased susceptibility to infections. In addition, severe iron depletion can lead to iron-deficiency anemia, which can cause other symptoms such as dizziness, headaches, and rapid or irregular resting heart rate.

Testosterone, Iron, and Thyroid Hormone Depletion in Cyclists disordered eating in female cyclists image

Tips to Mitigate Iron Depletion in Cyclists

To prevent or mitigate iron depletion, cyclists and endurance athletes can take several steps:


Eat a balanced diet: Add sources of sufficient iron-rich foods such as red meat, poultry, fish, beans, lentils, and leafy green vegetables. Haem iron found in animal protein is absorbed most efficiently.


Consider taking an iron or vitamin C supplement: Especially if you are at higher risk of iron depletion (such as women with heavy menstrual periods). Vitamin C increases iron absorption.

Avoid drinking tea or coffee with meals: It can inhibit iron absorption.

A word of caution!

Don’t guess or try to treat yourself! Get regular blood tests to monitor your iron and ferritin levels, and only take iron supplements under a physician’s care. 


Hemochromatosis is a hereditary disease that causes your body to absorb too much iron from the foods you eat. Your body has no natural way to rid itself of excess iron, so it gets stored in its tissues and organs. 


Hemochromatosis is the most common genetic disease in the Western world and can be life-threatening if undiagnosed and left untreated. It was for me. 


Please read my story so it doesn’t happen to you! Being an Endurance Athlete Almost Cost Me My Life—A Personal Story of Hemochromatosis

hemochromatosis image

Thyroid Hormone Depletion in Cyclist and Endurance Athletes

The thyroid gland produces hormones that regulate metabolism, energy levels, and body temperature. When you engage in prolonged periods of intense exercise, your body may experience what is known as thyroid hormone depletion. It occurs when your thyroid gland produces less of the hormones needed to regulate your body’s functions.


Symptoms of thyroid hormone depletion include fatigue, depression, weight gain, muscle weakness, and decreased stamina. In addition to these symptoms, thyroid hormone depletion can also lead to long-term consequences such as an increased risk of heart disease, a weakened immune system, increased risk of bone fracture.


Fortunately, there are strategies that you can use to prevent or mitigate thyroid hormone depletion. One of the most effective strategies is to ensure that you are getting enough rest and recovery time between training sessions.

Ensure you consume enough calories and nutrients to support your body’s energy needs. Eat a well-balanced diet rich in protein, carbohydrates, and healthy fats.


Supplementation with iodine, zinc, and selenium may also support thyroid function. These nutrients are essential for producing thyroid hormones, and you can find them in foods such as seafood, nuts, and seeds.


Thyroid hormone depletion in endurance athletes is a controversial topic. There’s a paucity of conclusive research. Despite this, it comes up frequently in endurance athlete forums and deserves mention. The above recommendations are common sense, and so is the urging to seek consultation with a healthcare provider if you think you may have the symptoms of thyroid hormone depletion. It’s a simple blood test.

Conclusion—Testosterone, Iron, and Thyroid Hormone Depletion in Cyclists

Cycling and endurance training can be an enriching and enjoyable endeavor, but we must care for our bodies to prevent hormone depletion. Testosterone, iron, and thyroid hormone depletion are common concerns for athletes, and there are steps to avoid these issues and ensure that you continue to perform at your best.


However, it’s important to remember that hormone levels can be complex and vary from person to person. Working with a healthcare professional or physical therapist to create a personalized plan that considers your unique needs and goals is essential. Medical supervision is critical in ensuring you’re making healthy choices supporting your body rather than putting it at risk. It’s as easy as getting some blood work and letting the professionals do the rest.


By paying attention to your testosterone, iron, and thyroid levels, you will be at the top of your game and achieve your goals. Remember, your body is your most valuable asset, so treat it carefully and respectfully.

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