The thyroid gland is a butterfly‑shaped organ in the front of your neck, just below the bony part of your larynx and in front of your windpipe. It has two main lobes, one on each side of your neck, that are connected across the middle by a thin band of tissue called the isthmus. Nodules often develop in that gland, and most are benign. Though benign they can still affect your thyroid function. However, some nodules are cancerous. In the event that a biopsy comes back positive for cancer cells, the decision is first surgical. If there was spread to the surrounding tissue or lymph node involvement, the next step is radiation. Usually following surgery, you will be placed on medication, as you no longer have a functioning thyroid.

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Nodules and cancer are one path to a non-functioning thyroid, but they are not the only one and they’re not what sidelined Emma Navarro. Navarro’s diagnosis is Hashimoto’s hypothyroidism. This is an autoimmune condition where the body’s own immune system mistakenly attacks the thyroid gland, gradually reducing its ability to produce hormone. No surgery, no nodule, no biopsy, just a thyroid slowly worn down by the body’s own immune response. This is actually the most common cause of hypothyroidism in the general population. It is a useful distinction for readers to understand, since “thyroid problem” covers a wider range of causes than people often realize.

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THYROID FUNCTIONS TO BE AWARE OF

The thyroid produces hormones: primarily T4 (thyroxine) and T3 (triiodothyronine). They regulate nearly every system in the body. This is exactly why a malfunctioning thyroid can produce such a wide, seemingly unrelated range of symptoms. A few of the thyroid’s key roles:

1. Metabolism Regulation: thyroid hormones set the pace at which your body converts food into energy. An underactive thyroid slows this process down, which is why unexplained weight gain, despite no real change in diet or training load, is one of the hallmark signs of hypothyroidism. This was exactly the symptom reportedly linked to Navarro’s case.
2. Energy Production: thyroid hormones influence how efficiently your cells produce usable energy. When thyroid function drops, fatigue often follows. This is not the kind rest easily fixes, but a persistent, heavy exhaustion that doesn’t track with sleep or training volume. For a professional athlete, this kind of fatigue is especially dangerous since it can be mistaken for overtraining or deconditioning rather than correctly identified as a medical issue.
3. Heart Rate and Cardiovascular Function: thyroid hormone helps regulate heart rate. Hypothyroidism commonly causes a slower resting heart rate. This matters significantly for an elite athlete whose training and performance depend on a well-calibrated cardiovascular system.
4. Temperature Regulation: an underactive thyroid often leaves people feeling cold when others around them don’t feel cold. The thyroid hormone plays a direct role in the body’s ability to generate and regulate heat.
5. Mood and Cognitive Function: hypothyroidism is strongly linked to brain fog, low mood, and difficulty concentrating. For an athlete, this can affect split-second decision-making and mental sharpness during competition.
6. Muscle and Joint Function: untreated hypothyroidism can cause muscle weakness, stiffness, and joint pain. These symptoms are a serious concern for any athlete relying on strength, flexibility, and quick recovery between matches.

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WHY HYPOTHYROIDISM MATTERS FOR ATHLETES

What makes a diagnosis like this especially difficult in professional sport is how easily its symptoms are misread. Fatigue, weight changes, and slower recovery are exactly the symptoms that get attributed to overtraining, poor conditioning, or simply “a bad season,” when the real cause is a medical condition requiring diagnosis and treatment, not just rest or a new training block. Navarro’s case is also complicated by a second diagnosis, RED-S (Relative Energy Deficiency in Sport), where the body isn’t receiving enough fuel for the demands placed on it. This is a combination that can create a genuinely confusing picture for both the athlete and the medical team trying to sort out what’s actually happening.

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THERE IS TREATMENT ONCE CORRECTLY DIAGNOSED

The encouraging news is that hypothyroidism, once correctly diagnosed, is highly treatable. Thyroid hormone replacement medication (commonly Levothyroxine, also known as Synthroid) can restore normal hormone levels, and with proper monitoring, many athletes can return to full competitive form. The harder part is often simply getting to the correct diagnosis in the first place, especially in a sport where fatigue and body changes are so often assumed to be part of the grind rather than a sign that something deeper needs medical attention. I have seen this in my profession as a physician, and I have personally experienced this with two loved ones. We wish Emma Navarro all the best and look forward to seeing her fully optimized in 2027.

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