The thyroid is a butterfly-shaped gland that sits at the front of your neck and sets your entire metabolic rate. Thus it controls your weight, whether you feel sluggish or energetic, mentally crisp or foggy, cheerful or blue, and is involved in managing everything from your cholesterol to your female hormones.
When your thyroid is not functioning well, you can feel dull, tired, constipated, gain weight, your skin & hair gets dry. Your hair can and even fall out. Your muscles and joints might ache, periods become irregular, you might have fertility problems, brain fog, sugar and carb cravings (because your body is desperate for energy!), high cholesterol even if your diet is fantastic!
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland, which is deep within the brain. TSH stimulating the thyroid glands to produce the hormone called T4. This hormone is exclusively produced in the thyroid gland and is dependant on having enough iodine, zinc, tyrosine, and cholesterol to be made. T4 is, for the most part, actually metabolically inactive. If you take Thyroxine, this is a synthetic version of the T4 hormone.
T4 is then released and circulated into the bloodstream a where it is converted into T3. T3 is the bomb! It is the metabolically active form of thyroid hormone; as a matter of fact, 8 times more biologically active than T4... When T3 binds to our cells with the help of vitamin D and iron. T3 turns out cells 'on" and regulates our metabolic rate, our thermostat and our heart rate; it's like juice or fuels or our DNA, RNA and mitochondria.
A percentage of T4 is converted into something reverse T3 (rT3) - a biologically inactive form of T3. Reverse T3 can lock onto T3 receptors on cells but evokes no response. Its hogs the parking spaces from active T3. It is speculated that reverse T3 is a natural ‘buffer’ against hyperthyroidism, a protective mechanism to prevent thyroid overactivity.
Yes. 80% of the body’s T4 toT3 conversation occurs in the liver, in phase 2 of the livers detox 0r conjugation process, so we want to ensure that we are feeding and supporting the liver to function well.
Sulforaphane is a sulphur-rich compound found in cruciferous vegetables like broccoli, bok choy, and cabbage is super crucial for the health of phase 2 liver pathways. Glutathione, sulphate, and glycine are the other primary molecules responsible for this process.
Reverse T3 (rT3) is an inactive form of T3 produced in the body, particularly during periods of stress. Reverse T3 and T3 are natural antagonists of each other, so they compete for receptor sites on our cells. If these receptor sites are occupied with reverse T3, then active T3 can’t bind to the cells to exert its effects. This may result in symptoms of hypothyroidism, even if T3 levels are within range. In these cases, it’s vital to assess and test for both reverse T3 and T3 itself, so the two can be considered in relation to each other. If reverse T3 is elevated with respect to free T3, it is vital to work out why!
An important note, your GP probably won't be interested in testing reverse T3, and Medicare will not rebate this test- but it's important to understand, so worth the out-of-pocket investment to run this test.
Reverse T3 is always produced as a natural consequence of thyroid hormone production- we'll all have some level of reverse T3. Even patients with a healthy, perfectly functioning thyroid will still be making reverse T3, which is normal. Patients with high T4 levels will produce more reverse T3, as it tries to protect us against the thyroid flipping to overactive function, called hyperthyroidism.
What isn’t normal is when excessive amounts of thyroid hormone are shunted towards reverse T3 production, leaving little leftover to be converted into the active thyroid hormone. This can happen for several reasons, including:
These factors contribute to increased conversion of T4 to reverse T3, potentially resulting in hypothyroidism or thyroid dysfunction symptoms. When looking at these factors, you can see how reverse T3 a clever evolutionary adaptation by the body.
During times of stress, famine or starvation (including eating disorders), reverse T3 production increases to slow the metabolic rate and conserve energy. Back in the cavemen era, this clever adaptation was protective when food supplies were low. In our modern world, this ‘stress’ may look like crash diets or emotional stress, but the effect on our thyroid hormones is the same: increased conversion of T4 to reverse T3 and a lower metabolic rate results. A similar effect is seen with glucocorticoid medications, such as prednisone, as these medications mimic the impact of our body’s stress hormone, cortisol, causing increased shunting of T4 towards rT3 production.
For most patients with suspected thyroid dysfunction, a thyroid function test assessing TSH, T4, and T3 will be sufficient to identify hypo- or hyperthyroidism. In addition, testing thyroid antibodies (such as TPO, Tg and thyroid receptor antibodies) helps determine whether there is an underlying autoimmune disease contributing to or causing this dysfunction. In most cases, reverse T3 is not tested, as T4 and T3 are considered more helpful in identifying and monitoring overt thyroid dysfunction.
When I usually advocate reverse T3 assessment, a patient is still experiencing symptoms of hypothyroidism, despite having a seemingly well-functioning thyroid. For example, suppose a patient is experiencing weight gain, low energy levels and hair loss despite normal thyroid function. In that case, I may recommend testing reverse T3, in addition to looking at other potential causes of their symptoms (such as low iron levels, poor blood sugar management and so on).
I also recommend reverse T3 testing if the patient has such symptoms and has been under prolonged stress or fulfil some of those criteria above for increased reverse T3 production. Identifying a raised reverse T3 can be helpful to understand why they may still be feeling hypothyroid, despite adequate thyroid hormone levels on bloods. Ultimately, if reverse T3 levels are raised, identifying the "why" is integral to addressing the problem, whether it's stress, insulin resistance, inflammation or nutritional deficiencies. Correcting these underlying factors will help regulate thyroid hormone metabolism and, ideally, improve the conversion of T4 to its more active form, T3.
Ultimately, if you’re experiencing unexplained symptoms of hypothyroidism or symptoms that don’t fit the picture as told on your blood tests, it’s worth investigating these further, and a conversation with your GP or naturopath may be all it takes to get the ball rolling!
Cruciferous vegetables, including kale, turnips, cauliflower and others, are rich in indole glucosinolates. In animal studies, this compound was found to degrade into a goitrin metabolite called thiocyanate that inhibits iodine uptake by the thyroid cell, hence inhibiting the synthesis of thyroid hormones.
The reality is, there is not enough good quality HUMAN data available that define the amount of cruciferous vegetable consumption that is needed to cause thyroid dysfunction. The goitrogenic potential of a plant or food depends upon the amount of active goitrogen present in it. Therefore, various procedures like soaking, washing, boiling and cooking can help in reducing the goitrogenic potency of these foods.
These, along with the intake of iodine supplements, are generally practised in areas where goitrogenic foods are routinely consumed. How far these measures are effective in reducing anti-thyroidal activity is still unclear. Patients suffering from hypothyroidism can avoid overconsumption/ excessive (> 500g per day) of raw cruciferous vegetables such as cabbage, Brussels sprouts, broccoli, cauliflower, mustard greens, kale, and turnip.
Heating or cooking denatures the goitrogenic compound into a less harmful metabolite, making these delicious vegetables 100% thyroid safe. Happy days!
Our daily diet should include thyroid boosting foods like those rich in iodine, amino acid tyrosine, minerals like selenium, zinc, copper, iron, various vitamins including B2, B3, B6, C and E.
Bajaj JK, Salwan P, Salwan S. Various possible toxicants involved in thyroid dysfunction: A Review. Journal of clinical and diagnostic research: JCDR. 2016 Jan;10(1):FE01.