Thyroid disorders and sports: how thyroid dysfunction affects physical activity

The thyroid is a small endocrine gland located at the front of the neck, near its base. It produces the hormones T3 and T4, which are essential for regulating many vital functions of the body.

“Thyroid hormones are true regulators of the body's energy balance. For people who practice sports, this means they directly influence:

• endurance;
• muscle strength;
• recovery capacity,” explains Professor Marugo.

In Italy, it is estimated that approximately 6 million people suffer from thyroid disorders, often related to either excessive or insufficient hormone production.

For this reason, recognizing and monitoring changes in thyroid function is essential not only for overall health but also for maintaining optimal athletic performance.

Thyroid disorders can generally be divided into three major categories: hyperthyroidism, hypothyroidism, and structural thyroid abnormalities. The conditions that most directly affect physical activity are hyperthyroidism and hypothyroidism.

Hyperthyroidism and sports

Hyperthyroidism is characterized by excessive production of thyroid hormones. Common symptoms include weight loss, insomnia, and hyperactivity. In athletes, however, the picture can be more complex.

“An excess of thyroid hormones induces a hyperdynamic state. This may lead to:

• increased heart rate;
• reduced endurance;
• higher risk of tachycardia and arrhythmias,” explains the specialist.

Hypothyroidism and sports

Conversely, hypothyroidism results from reduced thyroid hormone production and is associated with symptoms such as fatigue, weight gain, slowed movement, and mood changes.

“In athletes, hypothyroidism often presents as:

• reduced performance;
• difficulty recovering after exercise.

These are warning signs that should not be ignored,” cautions Professor Marugo.

Hypothyroidism and high cholesterol: an often-overlooked relationship

An aspect that is frequently underestimated, particularly among athletes, is the close relationship between thyroid function and lipid metabolism. Thyroid hormones play a key role in regulating cholesterol levels and the metabolism of fats and carbohydrates.

“In the presence of elevated cholesterol levels that cannot be explained by diet or lifestyle, thyroid function should always be evaluated. Hypothyroidism, even in its subclinical forms, may be an important cause,” notes Professor Marugo.

When the thyroid is underactive, total cholesterol and LDL cholesterol levels often increase, resulting in a higher cardiovascular risk. This is particularly relevant for physically active individuals, as it may negatively affect both performance and overall health despite an active lifestyle.

For this reason, when dyslipidemia cannot be otherwise explained, further diagnostic evaluation is recommended, including measurement of:

• TSH;
• FT3;
• FT4;
• thyroid antibodies;
• thyroid ultrasound examination.

Physical activity, especially when intense and prolonged, profoundly affects energy metabolism and directly involves the endocrine system, which regulates the production and release of hormones needed to sustain exercise.

During exercise, the body increases oxygen consumption and activates a series of metabolic adaptations that support performance and proper muscle function.

In this context, so-called Reactive Oxygen Species (ROS) are produced. These molecules are normally generated during cellular energy production. When present in controlled amounts, ROS also play a physiological role in training adaptation. However, excessive production may contribute to oxidative stress within muscles, negatively affecting strength, endurance, and recovery times.

“When a thyroid disorder is present, ROS production may increase even further,” explains Professor Marugo. “This can promote inflammatory processes involving muscles and tendons.”

Moreover, both hyperthyroidism and hypothyroidism may amplify these mechanisms by disrupting metabolic balance and impairing the body's ability to adapt to physical exertion, with potential consequences for performance and injury risk.

One of the greatest challenges is that thyroid dysfunction symptoms are often nonspecific and can easily be mistaken for normal fatigue.

“The problem is that many athletes interpret these signs as a physiological decline in performance. In reality, they may represent the warning signs of an endocrine disorder,” says Professor Marugo.

Among the most important signs associated with thyroid dysfunction are:

• reduced physical endurance;
• slow recovery after exercise;
• unexplained weight gain or weight loss;
• changes in heart rate;
• muscle weakness;
• excessive sweating;
• sleep disturbances.

Symptoms of hypothyroidism and hyperthyroidism in athletes

In cases of hypothyroidism, additional symptoms may include:

• reduced tissue oxygenation;
• poor muscle vascularization.

In cases of hyperthyroidism, common manifestations include:

• tachycardia;
• anxiety;
• difficulty maintaining performance levels.

In younger individuals, particularly during puberty, proper thyroid function is even more important because it directly influences growth and hormonal maturation.

“Undiagnosed hypothyroidism can interfere with hormonal development,” explains Professor Marugo. “In girls, for example, it may cause menstrual irregularities or disruptions of the hypothalamic-pituitary-ovarian axis.”

Furthermore, in young athletes, especially those competing at a high level, thyroid dysfunction can amplify the effects of physical stress on the body. This may result in delayed pubertal development, reduced recovery capacity, and, in more complex cases, broader endocrine imbalances.

For this reason, symptoms such as:

• persistent fatigue;
• declining performance;
• menstrual irregularities;

should never be underestimated. When indicated, an endocrinological evaluation should also be considered during adolescence.

Assessment of thyroid function is recommended when suspicious symptoms are present, but also as a preventive measure, especially for individuals who engage in regular or competitive sports.

“Thyroid evaluation should be part of the basic screening of athletes, particularly in the presence of family history or even mild clinical signs,” states Professor Marugo

Can people with thyroid disorders play sports?

Having a thyroid condition does not mean giving up physical activity. On the contrary, with proper diagnosis and appropriate treatment, it is possible to continue practicing sports safely.

“There are no absolute contraindications to sports participation,” concludes Professor Marugo. “However, it is essential to listen to your body and consult a specialist when something changes. The thyroid is a key regulator: maintaining its balance also means protecting athletic performance.”

The thyroid is a central component of both overall well-being and athletic performance. Recognizing the early signs of dysfunction allows timely intervention, helping to avoid consequences for both health and physical activity.

For athletes, the message is clear: do not ignore the signals your body sends, and include thyroid function assessment as part of your preventive health strategy.

*Source: Istituto Superiore di Sanità (ISS)