With our increased interest in health, the thyroid has started to get more and more attention. This is good news in light of the vital role the thyroid plays, affecting many aspects of your well being, and the myriad ways it can get disrupted.
This article will help you understand how the thyroid impacts your health and give you a list of some of the most common roadblocks to a healthy thyroid. Be aware that the thyroid is incredibly complex, which can make identifying exactly what is going wrong and how to fix it a bit of a challenge. Therefore, it’s essential that you work with a doctor you trust to solve thyroid issues and don't go it alone.
What Is The Thyroid?
The thyroid is a gland in the front of the neck that releases two hormones:
- T3, an active thyroid hormone and
- T4 an inactive thyroid hormone that is converted into T3 by the liver and kidney.
The thyroid is “told” to release T3 and T4 by a cascade of hormones that start with the hypothalamus in the brain. The hypothalamus releases Thyroid Releasing Hormone (TRH), which goes to the pituitary gland, binding with cell receptors and triggering the release of Thyroid Stimulating Hormone (TSH), which then triggers release of T3 and T4 from the thyroid.
Both T3 and T4 provide something called “negative feedback,” which means that as their levels rise, they “tell” the hypothalamus and pituitary to suppress release of TSH and TRH so that T3 and T4 remain within the correct physiological range. This is important because a thyroid disorder can be due to incorrect levels of any of these four hormones and the solution may vary depending on exactly which ones are out of balance.
Further, it’s possible for all thyroid hormones to be within normal physiological ranges, but an individual will still have symptoms of low thyroid function (hypothyroidism) and will need some sort of intervention in order to feel their best.
What Does The Thyroid Do?
The thyroid gland releases hormones that affect the following physiological processes:
Metabolic: Thyroid hormones regulate metabolic rate by affecting enzyme activity, body temperature, and appetite. Thyroid hormones also influence digestion and absorption of nutrients in the gut. They stimulate the breakdown of fat and glucose, and decrease cholesterol levels.
Cardiovascular/Respiratory: Thyroid hormones affect breathing rate, blood flow, and intake and consumption of oxygen.
Developmental: Thyroid hormones are necessary for normal bone growth and maturation. They also play a role in female menstruation.
How Do Thyroid Hormones Affect Body Composition & Fitness?
Because thyroid hormones regulate metabolic rate, they play a primary role in the ability to achieve a healthy body fat level. In fact, one reason people often plateau when losing body fat is that the thyroid responds to a calorie deficit by downregulating function and T3 levels drop leading to a decrease in body temperature so that the body burns fewer calories at rest.
Low thyroid hormone also reduces protein synthesis, lowering muscle repair. Low T3 is associated with low energy levels and a sense of sluggishness and fatigue, which makes people feel lazy, so they are less active, lowering activity-related energy expenditure.
Regarding fitness capacity, low thyroid leads to a decrease in cardiac function and impaired oxygen consumption, both of which impede athletic performance. This makes it critical that athletes with hypothyroidism get treated if they want to reach their potential.
Too much thyroid hormone can also be a problem, though it is much less common than hypothyroidism. Called hyperthyroidism, you get an elevated resting metabolic rate that leads to rapid loss of body fat and muscle wasting due to increased protein breakdown.
People with hyperthyroidism have a hard time sustaining body weight, which might sound favorable in a fat-loss obsessed nation but it drastically reduces quality of life, often leading to insomnia, elevated heart rate, and irritability.
What Are The Primary Roadblocks To Healthy Thyroid Function?
People often associate the symptoms of low thyroid function with aging:
- Fatigue and general loss of energy
- Reduced exercise tolerance
- Mental sluggishness
- Getting cold easily
- Dry skin, coarse or brittle hair and nails
- Sore joints and muscles
There’s an assumption that these physical maladies should just be expected and tolerated with age. In reality, they can be prevented with proper lifestyle habits and careful monitoring and treatment of the thyroid.
Aging increases the risk of thyroid problems for a couple reasons.
For women, hormone changes during menopause affect thyroid function. Estrogen and progesterone are the two hormones that regulate a women’s cycle and progesterone raises thyroid hormone. During menopause, progesterone drops first, with estrogen levels being more irregular, which is a combination that negatively affects thyroid function.
Additionally, there is an enzyme called deiodinase 1 (D1) that enables the conversion of T4 to the active T3, which is less active in women. This is one reason thyroid disorders are more common in women.
Men experience a decrease in DHEA release with aging, resulting in a drop in release of thyroid hormones and the conversion of T4 to T3. Additionally, inflammation develops and body fat increases with aging in both sexes, which negatively impacts thyroid function.
#2: Nutritional Deficiencies
Thyroid function and nutritional deficiencies tend to interact with one another, so that intake of certain nutrients keep the body from producing thyroid, while an insufficient thyroid keeps the body from making proper use of nutrients. Here are a few to look out for:
Iodine: The thyroid gland uses iodine to make T3 and T4, so if you aren’t getting enough, you’re levels will be low. Iodine is available in seafood and seaweed, as well as vegetables grown in iodine-rich soils. Even dairy products can provide iodine if the animals graze on plants growing in soils containing iodine.
Iodine is also often added to salt. This practice came about in the 1920s when intelligence data of military men found that soldiers from inland areas where iodine was not present showed significantly lower IQ levels than those with higher iodine intake who lived in coastal regions. In addition to its role in thyroid function, iodine is necessary for brain development.
Humans only require a tiny amount of iodine (150 mcg for adults, with higher intake between 220 to 290 mcg for pregnant/lactating women). However, if you avoid refined salt, don’t eat dairy, and don’t consume foods from the sea, you could be deficient.
Vitamin A: If the thyroid is underactive, it can’t properly convert beta-carotene into vitamin A. Carotene may accumulate in the body, preventing the formation of the hormone progesterone, which is essential for thyroid function. On the flipside, lack of vitamin A inhibits the production of TSH from the pituitary. The cells that release TSH degenerate with insufficient vitamin A. Lack of vitamin A also reduces thyroid ability to absorb iodine. This means that even if you have enough iodine in your diet, lack of vitamin A will reduce thyroid function.
Vitamin B2: Lack of vitamin B2 will depress release of the androgen hormone DHEA, resulting in lower levels of active T3.
Vitamin B12: Thyroid Hormone is necessary for your body to absorb B12 from food, which is a must because the body can’t produce B12. On the other hand, B12 is necessary to prevent anemia and maintain healthy neurological functions. Without adequate B12 you will die.
#3: Chemical Exposure
One of the biggest but least known roadblocks to a healthy thyroid is an overload of chemicals that disrupt iodine entry into the thyroid, impairing the production of T3 and T4.
Iodine is classified as a halogen—an element of the periodic table with chemically related elements. This means that iodine can be displaced in the body by high levels of three other halogens (bromine, fluorine, and chlorine) that have similar properties.
For example, many municipal drinking water supplies have fluoride added to them, which could contribute to thyroid dysfunction, especially if iodine intake is inadequate.
Then there is bromine—another halogen that can displace iodine—that is present as a food additive in brominated vegetable oil, which prevents separation of artificial dyes from water and other ingredients in sports beverages and soda. Bromine is also added to dough as a stabilizer. It is present in bread and other baked products. A high consumption of these foods could be problematic for thyroid function.
Finally, chlorine is often present in public water supplies, swimming pools, and various other environmental products such as fertilizers, matches, and fireworks. Obviously, completely avoiding halogens isn’t realistic. The key is to take steps to lower your exposure:
- Get a water filter—even a Britta will help.
- Avoid processed foods in favor of organic options when possible.
- When choosing packaged foods, opt for the most natural variety that is free of artificial additives like brominated vegetable oil.
- Avoid compounds like BPA, phthalates, and parabens that disrupt estrogen and testosterone because alterations in sex hormones will ultimately affect thyroid function.
#4: Calorie Restriction
Any time you have a calorie deficit for a sustained period of time, release of T3 gets reduced. The body is very responsive to a lack of incoming energy because it views it as a threat to survival. Back when we were hunter—gatherers and food sources were unreliable, the body needed a way to slow metabolic rate when calories were reduced due to lack of food. Altering thyroid function is a primary way the body does this.
You may recall the mention of the enzyme D1 from the part about aging. D1 is an enzyme involved in the conversion of T4 into T3. D1 levels drop in response to calorie restriction. This results in T4 getting converted into something called Reverse T3, which binds with T3 receptors, displacing the active T3 from doing its work.
Intermittent fasting appears to also impact thyroid hormone levels. For example, a study of young, trained men who adopted an intermittent fasting protocol in which they consumed all of their calories in an 8-hour period and then fasted for 16 hours found that T3 levels dropped significantly as did testosterone. This study didn’t utilize calorie restriction. The subjects maintained their calorie intake close to normal for the duration of the study, consuming an average 2,735 calories a day.
Obviously, if you want to lose body fat, a calorie deficit is necessary. Cycling calories so that you have a higher calorie intake once a week may reduce the drop in thyroid hormone when trying to lose body fat.
You also need to going too low in calories (below resting metabolic rate, which is around 1,600 calories daily) or combining calorie restriction with intermittent fasting because this added stress makes it more likely your thyroid will take a hit.
#5: Low Carb Intake
Lack of carbohydrates in your diet will also reduce thyroid function because insulin is needed for the conversion of T4 into T3. Of course, “low-carb” is a relative term so it’s useful to have some actual numbers.
Avoid going below the 50 grams-a-day-threshold if you have hypothyroidism. Keep your carbs in the 75 to 100 gram a day range if you want to lose fat and are worried about low thyroid function. People who are very active or training intensely may need more.
Another factor to consider is fat and protein intake. Compared to a low-carb higher protein diet (35 percent protein, 30 percent fat, 35 percent carbs), a low-carb, high-fat diet (10 percent protein, 55 percent fat, 35 percent carbs) led to a greater decrease in T3 due to the fact that insulin remains higher in response to the increased protein intake.
Where you get your fat from also affects thyroid function. High fat diets that contain a larger amount of polyunsaturated fat have more of a negative effect on thyroid function.
Therefore, if you’re trying a high-fat, lower carb diet and want to minimize the impact to the thyroid, try the following:
- Get the majority of your fat from monounsaturated sources (avocado, nuts, seeds, olive oil) and saturated fat (dairy and meat).
- Limit your with intake of polyunsaturated fat, only getting it from the healthiest sources (seafood).
- Avoid unhealthy polyunsaturated fats from refined oils (soy, corn, canola, vegetable blends).