Nine Factors that can Slow Down Your Thyroid and How to Correct Them

A healthy thyroid is key to keeping your body’s metabolism operating at a healthy rate – but what exactly is it? Your thyroid is a gland at the base of your neck that produces hormones that regulate the body’s metabolic rate, heart and digestive function, muscle control, bone density, brain development and mood. There are intricate pathways and feedback mechanisms in place to make sure your thyroid hormone production and conversion are operating optimally. That being said, there are a number of factors that can throw your thyroid hormone balance off or increase the likelihood of your immune system attacking it (this is called Hashimoto’s thyroiditis), resulting in underactive thyroid gland.
 
When your thyroid is underactive (also known as hypothyroidism), some of the main symptoms you may experience include weight gain, fatigue, sluggishness, sensitivity to cold weather, constipation, slow heart rate, dry skin, hair thinning or loss, menstrual irregularities, infertility, depression and high cholesterol. Your thyroid is stimulated by the thyroid stimulating hormone (TSH) to produce thyroid hormones: T4 (thyroxine) and T3 (triiodothyronine). Of the thyroid hormones produced, 80% is T4 and 20% is T3. T4 subsequently converts to the more active T3, which acts on target tissues. In hypothyroidism due to Hashimoto’s thyroiditis, labs show elevated TSH and low free T4. T3 is not routinely tested, but low T3 can be a sign of starvation, illness or nutrient deficiencies as well.
 
Here’s what you need to know about the modifiable factors that can make your thyroid underperform and how to correct them.
 

  1. Low vitamin D

 
Getting enough vitamin D has been linked to plenty of health benefits. It’s essential for bone health and preventing osteoporosis, and has also been implicated in autoimmune disease, blood sugar regulation and cancer. Having low levels of vitamin D has been correlated with autoimmune thyroiditis and research shows that this condition improves with vitamin D supplementation.
 
So, how can you get more vitamin D? Spend more time in the sun (15-30 minutes per day, depending on where you live, time of year and your skin type), and add foods that are rich in vitamin D to your diet and/or take vitamin D supplements. I generally recommend that my patients have their vitamin D level checked to help determine their supplementation requirement, so be sure to talk to your doctor about checking your vitamin D before starting supplementation.
 

  1. Too little or too much iodine

 
When it comes to maintaining a healthy thyroid, iodine can be a double-edged sword. Not enough iodine, something that 80% of my vegan friends are at risk for, and you’re in the danger zone for thyroid dysfunction. Too much iodine, on the other hand, has been linked to hyperthyroidism (overactive thyroid), worsening of hypothyroidism and autoimmune thyroiditis.
 
So, how much iodine should you be getting in your daily diet? The Recommended Dietary Allowance (RDA) of iodine is 150 mcg per day for adults, which is about ½ a teaspoon of iodized salt. Iodized salt is the mainstay of preventing iodine deficiency in the world, including the US.
 
On the opposite side of the spectrum, excess iodine can cause or worsen hypothyroidism or hyperthyroidism and autoimmune thyroiditis, so being aware of your consumption of high iodine foods such as seaweed, supplements containing iodine, medications (e.g., amiodarone) and getting iodinated intravenous contrast (administered when getting a CT scan with contrast), is important. Iodine containing foods are listed on the NIH website, although amount of iodine is only an approximation given the variation of iodine in soil as well as fertilizer use and irrigation practices. Individuals who have a strict sodium restriction due to medical conditions (e.g., congestive heart failure or hypertension) should seek other, non-salt sources of iodine.
 
If you are concerned that you might be at risk of iodine deficiency or excess, talk to your doctor. Iodine deficiency and excess can be diagnosed through a 24 hour urine test that measures iodine.
 
It’s also worth mentioning that, contrary to popular belief, you don’t need to stay away from soy to keep your thyroid healthy. As long as your iodine levels are normal, soy won’t have a negative impact on your thyroid. A literature review of 14 studies found that soy does not affect, or at most, very modestly affects thyroid function. When iodine intake is adequate, eating soy does not worsen thyroid function, so you can go ahead and have those edamame or indulge in a soy macchiato (my favorite). That being said, those who take thyroid medications and eat soy may require higher levels of the medication, due to lower absorption of synthetic thyroid hormone when soy is also consumed.
 

  1. Stress

 
Excess stress can have a negative impact on our body, and our thyroid is no exception. Why is that? Stress causes increase in the hormone cortisol, which reduces our thyroid stimulating hormone (TSH) and has been shown to lower T4 and the more active T3 thyroid hormone in rats. From an evolution standpoint, this makes sense, since your body conserves energy by slowing its metabolic rate when you are under stress. But if you’re in a constant state of stress and not dealing with it properly, it can be bad news for your thyroid.
 
Getting enough sleep, practicing meditation and mindfulness, exercising, eating a plant-rich diet and having a supportive community of friends and family all play a role in how our body reacts to stress. Working with a qualified healthcare practitioner to come up with a plan to effectively cope with stress can greatly reduce its negative physiological effects and improve wellbeing.
 

  1. Not eating enough

 
If you’re counting calories, make sure you don’t overdo it. Those who restrict their calorie intake are at risk of lowering their thyroid hormone T3 levels. One study found that reducing your calorie intake by 16-20% causes a significant decrease in thyroid hormone T3 levels. Low T3 is associated in increased likelihood of weight gain – this partly explains rapid weight gain after stopping a strict diet.
 
Just like stress, not giving your body what it needs to function puts it in energy conservation mode, so your metabolism slows down. Even if you are starting a diet or a new nutritional program, do not starve yourself – eat mindfully to satiety, and talk to a qualified health care professional and a health coach about the best plan for you. You can limit your calories without harming your thyroid. Any plan you choose to follow should be implemented thoughtfully and include not only dietary changes, but include movement, sleep and stress reduction.
 

  1. Low zinc

 
Zinc has a number of functions in the body. It plays important roles in cell division and immunity and is essential for conversion of thyroid hormone T4 to its more active form T3.
 
Vegetarians and those consuming excess alcohol are at higher risk of zinc deficiency than the general population. Medical procedures such as gastrointestinal surgery or conditions such as inflammatory bowel disease can also cause people to have trouble absorbing zinc.
 
The good news is that taking supplements can help individuals with zinc deficiency. In individuals with low T3 and zinc deficiency, zinc supplementation improved T3 levels. Supplementation with zinc also normalized TSH levels in children with low zinc.
 
If you think you might be at risk for zinc deficiency, seek testing from a qualified healthcare practitioner. Given that zinc supplementation can cause gastrointestinal symptoms and copper deficiency among other serious health issues, you’ll want to work closely with your healthcare provider to come up with a plan of action. Concurrent copper supplementation should be considered, especially at higher doses of zinc supplementation.
 
To eat your way to higher zinc levels, consult this list of zinc rich foods including beans, nuts, whole grains, seafood, poultry and red meat on the NIH website.
 

  1. Low selenium

 
Selenium is essential for the production and conversion of thyroid hormones and is responsible for cleaning up the inflammation that results from thyroid hormone production. In individuals with Hashimoto’s thyroiditis and selenium deficiency, supplementing with selenium reduces thyroid antibody levels. In pregnant women with thyroid antibodies, supplementation reduces subsequent inflammation of the thyroid gland (post-partum thyroiditis) and hypothyroidism.
 
It is recommended that selenium requirements be met through food – but it’s important to note that selenium in plant-based foods widely varies depending on the soil and plant uptake factors.
 
Some sources of selenium include Brazil nuts (3-4/day is sufficient), rice, sunflower seeds, eggs, poultry and seafood. Given the numerous benefits of a plant-rich diet, I generally recommend more of the plant-based sources and less of the animal based ones. You can find a more complete list of selenium sources on the NIH website.
 
More high quality trials are needed to determine the benefits and ideal setting of selenium supplementation. As with any potential cause of an underactive thyroid, it’s important to ask your doctor to have your selenium level checked and discuss if this is an appropriate supplement for you.
 

  1. Low iron

 
In my practice, it’s not uncommon to discover iron deficiency in reproductive age women, since blood loss from menstrual cycles can result in low iron levels. Iron is needed to make thyroid hormone, and deficiency can impair the production of thyroid hormone.
 
A small study showed that thyroid hormones were lower in women with iron deficiency anemia, compared to women with normal iron stores, and that supplementing iron-deficient women with iron partially improved their thyroid hormones. Vegan sources of iron include beans, lentils, spinach, tofu, chickpeas, tomatoes, peanut butter, brown rice and breakfast cereals fortified with iron. Aim to combine these non-heme iron sources with vitamin C (e.g., raw red pepper, orange, grapefruit or orange juice with no sugar added, raw green pepper, strawberries, tomato juice, etc) for better absorption. Animal-based sources include chicken liver, oysters, clams, beef liver and beef, turkey, tuna and eggs. For more information on iron sources, see the NIH website.
 
It’s important to consider screening for iron deficiency, if indicated, and treat. More studies are needed to clarify the nature of the relationship between supplementation and thyroid hormone levels as well as symptom improvement.
 

  1. Gluten and Celiac disease

 
Individuals with autoimmune hypothyroidism are 4 times more likely to have Celiac disease. Furthermore, people who have Celiac disease and ingest gluten may be at risk of nutrient malabsorption that could compromise their thyroid function. Some researchers suggest that individuals diagnosed with Hashimoto’s thyroiditis have diagnostic tests for Celiac disease.
 
According to American College of Gastroenterology, testing for Celiac disease is performed on individuals with gastrointestinal symptoms, such as diarrhea, fatty bowel movements, unexplained weight loss, bloating, malabsorption, unexplained elevation in liver enzymes, unexplained iron, B12 and/or folate deficiency. Those with type 1 diabetes or with a first degree relative with Celiac disease may also be tested. Celiac disease can be asymptomatic, or present with non-gastrointestinal manifestations (e.g., skin disorders, short stature, delayed puberty, recurrent fetal loss, reduced fertility, neurological symptoms or recurrent migraine headaches, among others), so it is important to talk to your doctor about whether your symptoms warrant further work up for Celiac.
 
If you are diagnosed with Celiac disease, you are able to take proactive steps to reduce inflammation, repair your gut and restore immune balance by eliminating gluten from your diet. In fact, a study showed that most individuals with thyroid disease who had concurrent Celiac disease and eliminated gluten, showed improvements or normalization in their thyroid tests.
 

  1. Low Vitamin A

 
Vitamin A plays an important role in vision, immune function, reproduction, growth and development and has been shown to suppress TSH. A small study of healthy women showed that supplementation with vitamin A increases T3, the more active form of thyroid hormone, and decreases T4, implying increased conversion from T4 to T3.
 
More research is needed to determine when vitamin A supplementation is appropriate and what doses are appropriate. Vitamin A deficiency (vitamin A < 20 μg/dL) in the US is estimated to be less than 1%, but optimal levels for thyroid function have not been defined. Vitamin A comes in different forms such as beta carotene and retinol, the active form. The enzyme that controls conversion of beta carotene to retinol (from animal sources), varies in different individuals, hence it is important to know that you are taking the active form, or converting properly to the active form. It’s also worth noting that vitamin A can cause toxicity and increase risk of cancer in smokers and asbestos workers, so if you are considering any supplements, talk to your doctor first. For more information on Vitamin A sources from food, function, and appropriate way to take it, please see the NIH fact sheet.
 
The above list captures the most common modifiable contributors to thyroid dysfunction. A basic understanding of essential components for optimal thyroid function can be key to avoiding or reducing thyroid disturbances and their impact on health. If you have been diagnosed with thyroid disease or suspect your thyroid is underactive, seek medical guidance for further testing. Diet and supplements are not a substitute for thyroid hormone treatment so please work with a licensed healthcare professional to help determine the best course of action for your condition.