Iodine and thyroid hormones for sports performance

Iodine and thyroid hormones are essential to sports performance and yet many athletes are iodine deficient.

Thyroid hormones perform many key functions in the human body including regulation of body temperature, metabolism and play an important role in how an athlete creates and uses energy. Thyroid hormones bind to receptors on each cell’s membrane surface and inside the cell at the mitochondria where energy is made. Binding activates the cell’s energy and metabolic functions.

Iodine is a key trace mineral stored primarily in the thyroid gland. The thyroid gland produces the key thyroid hormones thyroxine (T4) and triiodothyronine (T3), using iodine and other key nutrients such as selenium and tyrosine.  To further convert thyroid hormones into activated forms the body can use, sufficient levels of magnesium, iron, selenium, vitamin C and zinc are also required.

Key hallmarks of iodine deficiency and low thyroid function in athletes include:

  • Fatigue and low stamina can really cause havoc to an athlete’s training and racing season
  • Lethargy, muscle aches, cramps, pains and weakness
  • Low basal body temperature (temperature first thing in the morning)
  • Intolerance to cold weather
  • Cold hands and feet
  • Slow brain function, poor memory and “foggy” brain
  • Constipation
  • Joint pain
  • Thin, brittle hair or hair loss
  • Dry flaky skin
  • Menstrual disorders and fertility problems
  • Weight gain and slower metabolic rate

Iodine is primarily lost through sweat, although some are also excreted in the urine.  Some studies suggest athletes may lose more iodine through sweat in an hour of vigorous exercise than through their entire daily urine output.  High levels of sweating during exercise can deplete iodine levels and result in dehydration and poor performance.

The recommended iodine intake is 150ug/ day but some studies show on average athletes may lose nearly 50% of this requirement in sweat alone. Athletes living in more humid conditions (even without exercise) can lose a greater amount of sweat than those living in cooler environments.

Athletes performing at high intensity for prolonged periods of time, particularly in a humid environment, have a significantly increased risk of becoming iodine deficient if they don’t pay special attention to replacing this important nutrient.

What else can impact iodine and thyroid function?

It is important to keep in mind there are lots of things that impact the thyroid gland.

Chronic physical or emotional stress and high cortisol will result in elevations of another thyroid hormone called reverse T3 (rT3). Pesky rT3 inhibits our active thyroid hormone T3.

Heavy metals and chemicals, a low carbohydrate diet and fasting and selenium deficiency can also reduce T3 levels.  There are many chemicals and metals in our environment known as “endocrine disruptors” that inhibit healthy thyroid function. Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are common in our environment containments (in soil and food grown in that soil including meat, electronics, electrical cables, paints, plastics, furniture ) which can disrupt thyroid hormone signalling at the receptor level.

Perchlorate found in food and water inhibits the thyroid’s ability to absorb iodine from the bloodstream while long-term consumption of fluoridated drinking water is associated with hypothyroidism (low thyroid function).

Dioxins, BPA (found in cling wrap, drinking bottles and plastics) or bisphenols in tinned foods and plastic containers and plastic wraps, are also endocrine disruptors.

Non-stick cookware, fragrances, detergents, cosmetics and skincare, foods exposed to pesticides and herbicides, flame retardant material, new carpets, furniture and clothing may also be sources of endocrine disruptors.

When a female athlete has excess oestrogen, it may reduce the efficiency of thyroid hormone by 25%. Female athletes with high testosterone levels or insulin resistance may also have reduced thyroid efficiency due to a reduction in the globulin that carries thyroid hormone around the body (thyroid binding globulin) which means not enough thyroid hormone can circulate. But the hormone dance doesn’t stop there.

Low thyroid function due to low iodine or other nutrients can also cause receptor sensitivity issues with other female hormones such as progesterone causing PMS symptoms, irregular periods and fertility issues.

Cortisol up-regulates estrogen and high oestrogen also up-regulates cortisol which increases the binding of T4 up to 3 times, resulting in lower thyroid hormone activity, lowered metabolism and weight gain.

As thyroid hormones influence the tight junctions in the stomach and small intestine, athletes with low iodine and thyroid can also suffer from digestive complaints such as gas, bloating, diarrhoea or constipation and digestive infections.

Approximately 20% of our thyroid hormone T4 is converted to T3 in the gut by bacteria. So if digestion is disrupted and inflammation exists, the conversion will be impacted. Thyroid hormones also influence the tight junctions in the stomach and intestine that prevent large undigested molecules from passing into our bloodstream. Hence why thyroid abnormalities are also associated with leaky gut, food intolerances, constipation, reflux, heartburn, and dysbiosis (gut microbiome imbalance).

Thyroid hormones also influence the foundation of our immune system in the stomach called Gut Associated Lymphoid Tissue (GALT). GALT is made up of several types of lymphoid tissue that store immune cells, such as T and B lymphocytes. The majority of infectious agents invading the human body gain access through the gut and GALT protects us against these pathogens.  Therefore, an athlete can be more susceptible to infections if thyroid hormones are low or iodine deficiency exists. n

Other nutrients have an impact on iodine and thyroid function. Many athletes suffer from anaemia or low iron and believe their fatigue and poor performance may just be iron related. The situation is a double-edged sword as iron deficiency impairs thyroid hormone synthesis and low thyroid function impairs gastric secretions which reduce iron absorption from food.

Another tricky synergy exists between zinc, copper and thyroid function. Zinc is required for T4 and T3 production and therefore zinc deficiency may lead to low gastric secretions and low iron. Zinc and copper also antagonise each other so low zinc may lead to high copper.  Excess copper slows thyroid function and depletes zinc.

Iodine concentration in foods is variable depending on soil concentrations and the amount of fertilizer used with farming methods. Therefore, our food iodine content also varies greatly in grains, meats and vegetables. Although the daily recommended iodine intake is 150ug, it can still be tricky even when eating iodine food sources due to such variability.

Metabolic acidosis is a condition when the body’s pH is too acidic (pH of 7.35 or lower). This may occur in athletes from prolonged exercise at high intensity leading to lactic acid build-up. Chronic metabolic acidosis may decrease T4 and T3 and increase TSH concentrations and may lead to subclinical hypothyroid states.

  1. Tracking athletes’ basal (morning) body temperature can assist with identifying issues with thyroid function. Anything less than 36.4c suggests your thyroid may need some attention.
  2. Athletes should not rely on blood tests to confirm thyroid function status. Under activity of the thyroid gland results in low basal temperatures and symptoms of low thyroid function are not detectable by the standard laboratory tests-thyroid stimulating hormone (TSH), T4 and T3.
  3. Athletes should consume sufficient sources of iodine on a regular basis. Good food sources include seafood (wild sea fish contain more iodine than freshwater fish), kelp and other seaweeds (wakame, Kombu, Nori), kelp noodles, Sushi are a rich source of iodine. Other reasonable sources include milk and yogurt, navy beans, eggs, cranberries, strawberries and some meats.
  4. Since 2009 all packaged bread has added iodine in Australia although freshly baked bread may not disclose the amount added. Iodized salt is also available but keep in mind too much salt is not great for blood pressure and even sea salt and Himalayan salt contains 90% sodium chloride which is not desirable as chloride inhibits iodine absorption.
  5. Be mindful of high intake of goitrogenic vegetables. The cabbage family including cabbage, kale, broccoli, cauliflower, Brussels sprouts, radishes, turnips, watercress, spinach contain isothiocyanates (goitrogens) which may block the uptake and utilisation of iodine in the thyroid gland. Cooking these vegetables reduces the goitrogens and the likelihood of their impact.
  6. Although controversial, some evidence suggests soy supplements such as soy protein powders should be avoided if you have been diagnosed with low thyroid function as they may also reduce the genetic expression of the enzymes needed to produce thyroid hormones.
  7. Get your vitamin D levels checked. Vitamin D deficiency is common in Australia and in athletes with low body fat this issue can be even more prevalent as Vitamin D is stored in fat cells. Vitamin D is associated with hypothyroidism and thyroid autoimmune conditions while studies show serum vitamin D > 125 is associated with a 30% reduced risk of hypothyroidism.
  8. Get your hormones, cortisol, iron, zinc, copper and iodine levels checked.
  9. Improve your gastric acid secretions by consuming bitter foods (endive, rocket, radicchio, chicory, dark chocolate) on a regular basis or sip lemon in water or apple cider vinegar before meals.
  10. Reduce your exposure to endocrine disruptors by drinking filtered water, installing filters on shower heads, choosing natural water sources to swim in rather than chlorinated pools, eating pesticide-free or ideally organic foods, choosing organic personal care products, cosmetics and detergents, avoiding storage of food in plastics and instead use wax wraps and choose low emitting products when renovating or building your home.

If you suspect you may be suffering from iodine deficiency or reduced thyroid function, consider making an appointment with the Athlete Sanctuary to help navigate your recovery process.

About the Author: Kate Smyth is a Sports naturopath, nutritionist and female-centric running coach. She is the founder of the Athlete Sanctuary- a holistic healthcare clinic for athletes of all levels and sporting codes. Kate has a thirst for knowledge with two bachelor’s and a master’s degree under her belt. She has been involved in sports for many decades and competed for Australia in the Commonwealth Games and Olympic Games marathons with a personal best time of 2 hours 28 minutes. For more information visit www.https://