Thyroid Imbalance in Runners: A Look at the Impact of Training on Thyroid Levels

A thyroid disorder can be a vexing problem for a runner.

The initial symptoms of a problem with thyroid hormone levels are quite vague, and even once it’s diagnosed, thyroid levels have to be closely monitored and managed to ensure good health.

The thyroid hormone essentially sets the “speedometer” for many of the body’s intrinsic functions.

• When thyroid hormone levels are too high, a condition termed hyperthyroidism, you will experience symptoms like weight loss, tremors, anxiety, and a racing heart rate.

• In hypothyroidism, when thyroid hormone levels are too low, you might gain weight, become constipated, be overly sensitive to cold temperatures, and feel fatigued or depressed.

In both cases, thyroid disorders can be diagnosed by a blood test.  Paradoxically, people with both conditions usually end up taking thyroid hormones: hypothyroidism is treated by directly supplementing the body’s depressed production of the hormone with a synthetic form, while hyperthyroidism is treated by attacking the thyroid gland itself, which eventually slows or stops its thyroid hormone production after treatment.

Since a healthy thyroid gland regulates levels of thyroid hormones dynamically to respond to myriad changes in the body, people taking synthetic thyroid hormones often have to modulate their dosage over time.  As we’ll soon see, there is evidence that this can become a particularly thorny problem in athletes due to the unique stresses they subject their bodies to.

Because the thyroid can be such a difficult problem for runners, this week’s article digs into the scientific literature to see what we can learn about managing thyroid disorders in runners.

The research supporting thyroid treatment and running

While there is not much in the way of authoritative reviews on thyroid conditions in athletes, it’s clear that we as runners aren’t immune to them. Many top-level elite athletes, including Galen Rupp and Adam Goucher—two of the best American 5k and 10k runners in recent history— reportedly have hypothyroidism. Approximately 5 percent of the general population is affected. While most of these cases are termed “subclinical,” meaning that the levels of thyroid hormone are only borderline-low, the medical community debates about whether treatment is necessary.

• A 2001 review study by Michael McDermott and Chester Ridgway at the University of Colorado Health Sciences Center argues strongly that mild thyroid failure, the cause of subclinical hypothyroidism, should be treated in order to prevent many of the health problems associated with lowered thyroid hormone levels later in life.

• On the other hand, a 2007 Cochrane Collaboration meta-analysis found only marginal benefits when subclinical hypothyroidism was treated.

• For unknown reasons, women are about four times more likely to suffer from hypothyroidism (both clinical and subclinical).

The impact of training on thyroid levels

When it comes to thyroid levels in runners, there’s no solid understanding of the effects of endurance training.  A few small studies which have examined the effects of endurance exercise on thyroid hormone levels have indicated that training can at least influence thyroid hormone profiles.

A 1982 study of 29 healthy women running about 14 miles a week first tested their thyroid levels, then instructed them to increase their mileage to 30 miles a week for two weeks. After the increase in mileage, their hormone levels were measured again.

The researchers found that the subjects’ thyroid profiles were impaired, consistent with other physical and psychological stress results.

Fortunately, the authors of this initial study were far-sighted enough to conduct a follow-up study two years later. The same group of women increased their training to 50 miles a week, and their thyroid function normalized; the thyroid impairment was only a transient response to the stress during a training increase.

Later research published in 2003 by L. Baylor and A. Hackney confirmed that intense training has an effect on thyroid hormone levels in female athletes, but interestingly, their study demonstrated that not all women respond the same.7 17

Female athletes underwent an intense training regimen of running, rowing and weight lifting for five months. Thyroid hormone levels remained stable in 7 of the women, while they dropped in 10 of them. This highlights the complex and poorly-understood nature of thyroid issues, particularly among women. Further research has shown that dietary factors, like iron levels and zinc intake, can also influence thyroid hormone levels.8, 9

The only thing that’s clear is that more research is needed on thyroid problems in athletes.

• Are endurance athletes, especially females, more prone to thyroid problems than the general population?
• Can intense training affect the balance of thyroid hormone in runners who already have hypothyroidism?
• And do runners with thyroid problems respond to physical stresses the same way healthy runners do?

These are all questions that urgently need to be answered.

Final points

For now, the best advice from the medical community is to:

• Find a good endocrinologist that understands your needs as a runner
• Closely monitor your thyroid-stimulating hormone (TSH) and free thyroxine (free T4 or fT4) levels on a regular basis

Highly competitive athletes report that, while a solution may not present immediately, you should consistently take care of your body the old-fashioned way (a healthy diet and enough sleep), and modulate thyroid dosage with an endocrinologist.

Indeed, as many readers likely know, thyroid imbalance has not barred Galen Rupp from achieving a streak of consistent and healthy 10,000 m running that took him all the way to the podium at the 2012 Olympics.