Everything you ever wanted to know about the thyroid, from testing to drugs to the foods you need to eat for optimal function.
Here's what you need to know...
- Your thyroid levels can be either optimized or harmed by actions you take.
- The thyroid needs iodine, either from iodized salt, certain foods, or from supplements.
- Optimized thyroid levels promote fat loss, as well as maintenance of a lean condition.
- T4 metabolites can work towards reversing adverse changes to gene function associated with metabolic disorder.
- For females, iron deficiency is a likely cause of thyroid deficiency.
The All-Powerful Thyroid
Your thyroid is tricky. And while oral dosing of thyroid hormone can be beneficial, it can also be very harmful if done incorrectly.
Whether for body composition, athletic performance, or health, three things must be true, regardless of what supplement or drug we might be talking about:
- Your cells must be provided with the right raw materials in suitable amounts.
- Your cells must receive signals which work towards optimizing your goals.
- Your genes must function as well as possible. This varies all the time, and can be changed.
Too often, one or more of these are missing from a program. Cover the bases, and get better results.
The Thyroid Needs Iodide
About 12% of Americans are seriously deficient in iodide as measured by urinary analysis. Many more are moderately deficient or sub-optimal. So while diet alone can provide good iodide intake, very often it doesn't. It's worth giving your food choices and iodized salt intake a quick lookover.
If most of your food is homemade and salted with a medium-to-heavy hand with iodized salt, you should have good iodine intake already. If not, then you should increase it.
How much iodized salt is needed, if it's your principal source of iodide? When iodized salt is at full potency, it takes about 2 grams or about half a teaspoon of iodized salt (about 936 mg sodium) to meet your rock-bottom minimum for iodide consumption.
However, about half the time, iodized salt brands do not meet label claim for iodide, so it could take somewhat more to meet a bare minimum.
Generally, fast foods, processed foods, and restaurants don't use iodized salt. If a label reads merely "salt" instead of "iodized salt," it's not iodized. And "sea salt" contains little iodide.
If you aren't consuming much iodized salt at home, increasing your intake is likely to benefit you. I recommend 300 mcg of iodide per day, but somewhat more is fine.
How Much Iodized Salt Is Too Much?
Overdosing with iodized salt is unlikely unless you use a really heavy hand.
The NIH recommends 1100 mcg (1.1 mg) of iodide a day as a maximum intake, and the evidence strongly supports consuming no more than this. There's absolutely no reason to consume more than this on an ongoing basis, and a good reason not to do so.
Greater intake than this can cause hypothyroidism. It may not take even this much. A large study in China found intake of 0.8 mg/day to be associated with hypothyroidism.
If using full-potency iodized salt as the sole source of sodium, 0.8 mg iodide/day wouldn't be reached until consuming about 4945 mg sodium/day. This is about a full tablespoon. I generally like seeing athletes consume about 4000 mg sodium/day, so this works out fine.
I'd prefer, however, you limit iodized salt intake to no more than about half a tablespoon per day, as I see no reason to push iodide to the extreme.
In practice, some iodized salt is short of full potency, so expect some variation. The above range allows for normal variation. It does assume, however, that the salt is added after cooking, not before.
For the ladies, if pregnant I'd recommend avoiding excess iodide intake, as can happen with consumption of seaweed or over-supplementation with iodide.
What Foods Provide Plenty of Iodide?
As a way of looking at how iodine-rich some foods are, you could meet a 150 mcg/day requirement by consuming any one of these in about the following amounts:
- 2.5 cups of milk, yogurt, or cottage cheese per day
- 2.5 baked potatoes with skin
- 12 eggs
- 13 ounces of shrimp or of "average" saltwater fish
- 13 ounces of turkey
Beef, chicken, pork, rice, most wheat products, fruits, and vegetables are too low in iodine to be major sources. Seaweed or kelp are extremely rich but aren't common foods in America.
Also, whey protein concentrate and micellar casein are pretty rich in iodide. It takes only about 80 grams of these proteins, give or take, to provide 150 mcg iodine.
So if your diet has several of the above things or a lot of even one of them, you won't need iodized salt or a supplement. But if your diet is strong on things like beef, chicken, vegetables, pasta, and fruits and weak on the above, then iodized salt or a supplement will probably be beneficial.
You'll find varying claims on wheat products. Some tables show a wheat product or two as good sources. But when high in iodide, it's the additives that are providing it, and additive use varies greatly between products. For example, bread slices vary from a useless 2.2 mcg to a potentially-problematic 587 mcg, with low values being more common than high.
Worse yet, bread additives may include potassium bromate, which actually works against your thyroid rather than for it. So, don't count wheat products as reliable contributors, and particularly not bromate-containing bread.
Vitamin And Mineral Supplementation For Thyroid
Vitamin D deficiency is associated with hypothyroidism, and appears able to cause it. Unless you get a good deal of sun on a regular basis, there are many benefits to supplementing with Vitamin D at 4000 IU/day. Thyroid function likely is among them.
With regard to minerals, iron or selenium deficiency can result in thyroid impairment. If you're male, iron deficiency is fairly unlikely. If anything, your iron levels are more likely to be too high. Generally, men shouldn't supplement with iron unless a need is proven by blood test.
I haven't personally seen selenium correct a thyroid problem, but it's valuable for other reasons.
So how important is mineral supplementation? If you're a man, a lack of iron or selenium might be non-optimal for thyroid function, but generally I don't think deficiency of these is a substantial cause of male thyroid problems. And if your diet already suffices for these minerals, more won't give you more thyroid hormone.
However, if you're female, iron deficiency is a likely cause of thyroid deficiency.
Dieting And Thyroid
Thyroid output and conversion of T4 to T3 can be strongly affected by macronutrient intake and caloric intake.
Briefly, protein and carbs are stimulatory, while fat does nothing to sustain thyroid output or conversion of T4 to T3, and excessively low caloric intake can be devastating.
How low? I recommend not going below a daily intake of 12 kcal/day per lb of in-shape bodyweight. For example, if you weigh 230 and would be in good shape at say 200, take 200 and multiply it by 12 to get 2400 cal/day as a minimum. If fat loss is not fast enough at this intake, increase physical activity rather than cut calories further.
On a low carb diet, keep protein high to maintain thyroid function.
What cells do, and therefore ultimately what the body does, depends on the control signals they get.
Damaged, confused, harmful, or wrong control signals in the body won't get you where you want, and especially not when thyroid signals aren't right.
So what does thyroid signaling do? A whole lot. A quick summary:
Inadequate Thyroid Signaling
- Reduced metabolic rate, by about 25% in many instances
- Reduced expression of genes important to fat metabolism
- Impaired insulin sensitivity
- Reduced expression of genes important to glucose metabolism and transport into muscle
Excessive Thyroid Signaling
- Increased heart rate, for example +24% from 75 mcg T3/day
- Increased metabolic rate, for example +13% from 75 mcg T3/day
- Increased fat loss
- Increased expression of genes important to fat metabolism
- Increased catabolism of muscle
- Impaired insulin sensitivity, as occurs also with inadequate signaling
- Increased expression of genes important to glucose metabolism and transport into muscle
Factors Impairing Thyroid Signaling
Thyroid levels or signaling can be impaired by stress, depression, low testosterone, low GH, diabetes, obesity, history of major weight loss, chronic pain, and/or high levels of C-reactive protein, TNF-alpha, IL-1, and IL-6 (all of which are related to inflammation.)
The answer to all of these is to reduce or eliminate these problems. When too much of these things are going on, thyroid related problems are likely, even if doctors say blood tests are normal. This is because levels of thyroid hormones within cells can be impaired by these conditions even when blood levels are normal.
In one of the above conditions, however, often the right thyroid treatment can alleviate the related problem. This problem is depression. As that's a complex subject, it'll have to be in another article. In the case of the other conditions, the direction of treatment needs to be of the conditions themselves, with thyroid signaling improving after or as the problem is improved.
High TSH Promotes Metabolic Disorder And Obesity
TSH itself isn't a thyroid hormone; it's the hormone that tells the thyroid to make thyroid hormone. When the thyroid is responsive, TSH production is moderate. When the thyroid is unresponsive, TSH levels increase in an attempt to compensate.
In and of itself, that could be okay if this yielded good T3 and T4 levels and nothing else happened. But very unfortunately, something else does happen.
High TSH signals cells in a way that changes expression of multiple genes, changing their function greatly – in the direction of metabolic disorder and obesity.
Poor thyroid function not only slows metabolism directly due to low stimulation by T3, but changes gene function in the body towards a state where obesity is the equilibrium condition.
Some changes occur from low T3 and others from high TSH. Once this occurs, if the changes aren't reversed it's far more difficult for the person to lose fat and have a normal metabolism.
Signs and symptoms that could suggest low thyroid include unreasonably difficult fat loss, depression, intolerance to cold, brain fog, low body temperature, undue fatigue, diabetes, obesity, recent major fat loss, chronic pain, and/or chronic inflammatory condition.
If male and not taking thyroid hormone, then without any of these I wouldn't spend the money or time to get a thyroid test.
If female, the same is true except that menstrual problems and genuinely unusual water retention problems could be additional reasons to seek a thyroid test.
A large majority, I'd say over 80%, of those who are free of the above problems indeed have no thyroid issues at all.
For most, the main concern regarding the thyroid should be with regard to iodide intake, and if applicable, excessive caloric restriction or a high fat / low protein diet. If you're guilty of either of those, then correcting that will be the biggest thing you ever took home from any nutrition article!
Range of Thyroid Levels Indicating Proper Signaling
Thyroid panel interpretation can be easy, or very hard indeed. Where it can be easy is when you know the right things to focus in on, and where the situation is either clearly good or clearly a problem. So let's limit ourselves to what is clearly good:
- Free T3: Middle to the upper part of your test's normal range
- Free T4: Middle to the upper part of your test's normal range
- TSH: Preferably no more than 2, even more preferably 1.5 or less
Doctors often omit testing for free T3, but the value really is needed for good diagnosis. Total T3 can be deceptive, as most of the total is inactive.
You don't need total T3 or total T4. If the free values are fine then the total values don't matter. Likewise for T3 Uptake and Free Thyroxine Index: you don't need them.
If free T3 is good, then TSH at the lower end is fine, or even beneficial. (I'm assuming thyroid medication isn't being taken.)
Overly high TSH generally shows poor thyroid function, requiring abnormally high stimulation to compensate or partially compensate.
High TSH has adverse effects of its own on metabolism, working towards causing metabolic disorder.
If test values aren't quite so good as these, there's no sharp transition between "good" and "bad." It becomes a very slowly sliding scale, with different meanings in different situations. If your results are greatly different from the above and if actions can improve those values, they'll be worth taking.
Reverse T3: Should It Be Tested?
Reverse T3 is an optional test. Most doctors omit it, and usually that's fine.
If you do obtain this value and its ratio with T3 is out of range, there are various possible causes. If not suspecting any particular health problem, I wouldn't spend the money on a reverse T3 test.
Thyroid Hormone Products
Oral thyroid hormones are available as prescription drugs, as "research chemicals," and as pure chemical materials. The most commonly available forms are T3, T4, and Armour Thyroid which contains both T3 and T4.
Of prime importance to consider with T3 and T4 products is the fact that they don't have high chemical stability. Even the major pharmaceutical companies have had issues with stability in tablets, and use particular techniques to address this.
Expired product is likely to have lost potency, and generic products may not hold potency even up to the expiration date.
Research chemical products very typically are of reduced or even greatly reduced potency, and can lose potency rapidly, particularly when provided as liquids.
Unfortunately, many users of such products have posted dosings which are completely wrong. They think they've been taking doses such as 150 mcg T3/day and advise others to do the same, but their reported experiences are from much less actual amount of drug.
Dosing of Pharmaceutical Thyroid Products
Where the concerns aren't symptoms of thyroid deficiency but rather enhancement, the protocol I favor uses these dosing levels:
- Optimizing body function: Morning dosage of 12.5 mcg T3.
- Light cycle: Morning dosage of 12.5 mcg T3, and evening dosage of 50 mcg T4.
- Heavier cycle: Morning and evening doses of 12.5 mcg T3, and daily T4 dose from 50-200 mcg/day.
Positive effect over time at Level 1 can become very significant, yet I know of no instance of any adverse side effect. There's no detectable effect on thyroid function at this dosage. Usage may be continued as long as desired.
Level 2 provides faster fat loss effect, generally without noticeable adverse effect. TSH is reduced but not shut down, and often remains in the normal range.
Level 3 is obviously more intensive. If any substantial increase in heart rate occurs, dose should be reduced. TSH is likely to be low during the cycle.
For Levels 2 and 3, limit the cycle to 8-12 weeks, but duration can be extended past this. There's no exact science on suppression versus amount and duration of use, but it's a documented fact that extended use at suppressive levels can result in an extended period of only partial recovery.
Can I Adjust the Dose To Get TSH Where I Want?
Absolutely. If having high TSH, adjusting dose to lower it to 1-2 mU/L has a great deal to say for it, and has been suggested repeatedly in the medical literature as potentially beneficial. I know of no study, however, proving the benefit. My opinion is that it would be valuable to do.
Alternatively, if the purpose is to elevate free T3 over a long period without driving TSH below normal, TSH could be evaluated and dose could be limited accordingly.
If health is the goal, avoid driving either free T3 or T4 over the high end of the normal ranges, and most preferably would aim for mid-high.
What About Frontloading T4?
How much T4 does your body have in it after taking, say, 100 mcg of T4? Well, if it's your first dose, then about 100 mcg. Simple enough.
But when you're about 6 weeks into taking T4, when you swallow a daily dose there are already about a week's worth of earlier doses still in the body, still active!
So the effect of T4 doses will start out being only about 1/7th as strong as will be the case later. Even one or two weeks into the program, the effect will be only partial.
For many drugs with a long duration of action like T4, frontloading is a way to account for this. In order to promptly get body levels to where they should remain, on Day 1 an extra amount is taken which corresponds to the above buildup. But T4 is a drug you absolutely don't want to overdose. You don't want to take a week's worth of T4 on Day 1 even though, most likely, it's about the correct amount.
A good solution is to double dose T4 during the first four days of use. This brings levels to the steady state in about 5 days instead of a month.
T3 is fast acting and absolutely no frontloading compensation should be made.
So when using the above schedules for combining T3 and T4, double the T4 in the first four days, but keep T3 the same.
How Much T3 Can I Use?
If using T3 alone, a maximum and entirely sufficient amount is 75 mcg/day. This amount typically gives substantially elevated heart rate, enough so to limit dose. I don't prefer for dosing to be this high.
100 mcg/day of genuine product typically greatly accelerates muscle loss and can cause weakness in the gym. Dosing should not be this high. Even 50 mcg/day is ordinarily entirely sufficient to speed fat loss, and is a recommended maximum.
T3-only thyroid cycles are effective for fat loss and can be safe. My preference for combining T4 is not from efficacy, but from consideration of signaling systems in the body. There's a point to the body having T4 present as well as T3. But inclusion of T4 isn't mandatory for bodybuilding results.
Why Not Jack Up Thyroid Dosing Higher?
Increased muscle burning, cardiac stress, and likelihood of impairing insulin sensitivity.
I'd recommend more physical work and/or better attention to diet and/or C3G instead. If your fat loss results are not excellent within the above recommendations, then I'd look at the diet, at increasing physical work done, or adding C3G.
If I Do Only One Thing, What Should It Be?
Evaluate your diet very approximately. There's no need to do any calculations at all.
Do the iodine-rich foods in the list make up a major part of your daily diet? If so there's no need to supplement with iodide or to use iodized salt.
If these foods are fairly light in your diet, then use iodized salt, half a teaspoon to half a tablespoon per day, or take an iodine-containing supplement.
- National Report on Biochemical Indicators of Diet and Nutrition in the U.S. Population 1999-2002. United States Center for Disease Control.
- Consequences of excess iodine. Nat Rev Endocrinol. 2014 Mar; 10(3): 136-142.
- More than adequate iodine intake may increase subclinical hypothyroidism and autoimmune thyroiditis. European Journal of Endocrinology (2011) 164 943-950
- Iodine intake as a determinant of thyroid disorders in populations. Best Pract Res Clin Encocrinol Metab. 2010 Feb;24(1):13-27
- Iodine toxicity from soy milk and seaweed ingestion is associated with serious thyroid dysfunction. Med J Aust. 2010 Oct 4;193(7):413-5.
- Iodine Excess as an Environmental Risk Factor for Autoimmune Thyroid Disease. Int J Mol Sci. 2014 Jul; 15(7): 12895-12912.
- Sources of dietary iodine: bread, cows' milk, and infant formula in the Boston area. J Clin Endocrinol Metab. 2004 Jul;89(7):3421-4.
- Vitamin D Deficiency and Its Association with Thyroid Disease. Int J Health Sci (Qassim). 2013 Nov; 7(3): 267-275.
- Moderate weight loss is sufficient to affect thyroid hormone homeostasis and inhibit its peripheral conversion. Thyroid. 2014 Jan;24(1):19-26.
- Dietary-induced alterations in thyroid hormone metabolism during overnutrition. J Clin Invest. 1979 Nov; 64(5): 1336-1347.
- Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism. 2002 Jul;51(7):864-70.
- Effect of low-carbohydrate diets high in either fat or protein on thyroid function, plasma insulin, glucose, and triglycerides in healthy young adults. J Am Coll Nutr. 1985;4(4):451-9.
- The role of dietary fat in peripheral thyroid hormone metabolism. Metabolism. 1980 Oct;29(10):930-5.
- In Vivo Regulation of Human Skeletal Muscle Gene Expression by Thyroid Hormone. Genome Res. 2002 Feb; 12(2): 281-291.
- Triiodothyronine Acutely Stimulates Glucose Transport into L6 Muscle Cells Without Increasing Surface GLUT4, GLUT1, or GLUT3. Thyroid. 2012 Jul; 22(7): 747-754.
- Genome-wide Association and Replication Studies Identified TRHR as an Important Gene for Lean Body Mass. Am J Hum Genet. 2009 Mar 13; 84(3): 418-423.
- Effects of Five-Year Treatment with Testosterone Undecanoate on Metabolic and Hormonal Parameters in Ageing Men with Metabolic Syndrome. Int J Endocrinol. 2014; 2014: 527470.
- Metabolic effects of androgen deprivation therapy. Korean J Urol. 2015 Jan; 56(1): 12-18.
- Why Can Insulin Resistance Be a Natural Consequence of Thyroid Dysfunction? Journal of Thyroid Research. Volume 2011, Article 152850.
- Adipose tissues and thyroid hormones. Front Physiol. 2014; 5: 479.
- Thyrotropin and Obesity: Increased Adipose Triglyceride Content Through Glycerol-3-Phosphate Acyltransferase 3.Sci Rep. 2015; 5: 7633.
- Obesity, energy regulation and thyroid function - Is borderline elevated TSH-level the cause or secondary phenomenon of obesity? Nuklearmedizin. 2008 (Vol. 47): Issue 5 2008 (179-224).
- Small Differences in Thyroid Function May Be Important for Body Mass Index and the Occurrence of Obesity in the Population. JCEM. Volume 90, Issue 7.
- Diminished energy requirements in reduced-obese patients. Metabolism. 1984 Feb;33(2):164-70.
- Urinary iodine is associated with insulin resistance in subjects with diabetes mellitus type 2. Exp Clin Endocrinol Diabetes. 2012 Nov;120(10):618-22.
- Screening and Treatment of Subclinical Hypothyroidism or Hyperthyroidism. Comparative Effectiveness Reviews, No. 24.
- Thyroid Hormone Concentrations, Disease, Physical Function, and Mortality in Elderly Men. Clin Endocrinol Metab. 2005 Dec;90(12):6403-9.
- T3/rT3-Ratio is Associated with Insulin Resistance Independent of TSH. Horm Metab Res 2011; 43(2): 130-134
- Effect of caloric restriction and dietary composition of serum T3 and reverse T3 in man. J Clin Endocrinol Metab. 1976 Jan;42(1):197-200.
- Cold stress, reverse T3 and lymphocyte function. Alaska Med. 1998 Jul-Sep;40(3):55-62.
- Reverse T3 does not reliably differentiate hypothyroid sick syndrome from euthyroid sick syndrome. Thyroid. 1995 Dec;5(6):435-41.
- FSH and TSH in the Regulation of Bone Mass: The Pituitary/Immune/Bone Axis. Clin Dev Immunol. 2013; 2013: 382698.
- Thyroid Hormone Crosstalk with Nuclear Receptor Signaling in Metabolic Regulation. Trends Endocrinol Metab. 2010 Mar; 21(3): 166-173.
- Mechanisms of obesity-associated insulin resistance. Genes & Dev. 2007. 21: 1443-1455.
- Differential 3,5,3'-triiodothyronine-mediated regulation of uncoupling protein 3 transcription: role of Fatty acids. Endocrinology. 2007 Aug;148(8):4064-72
- SIRT1 is a Direct Coactivator of Thyroid Hormone Receptor β1 with Gene-Specific Actions. PLoS One. 2013; 8(7): e70097.
- Calorigenic effects of growth hormone: the role of thyroid hormones. J Clin Endocrinol Metab. 1996 Apr;81(4):1416-9.
- Recovery of Pituitary Thyrotropic Function after Withdrawal of Prolonged Thyroid-Suppression Therapy. N Engl J Med 1975; 293:681-684