I’m wondering a few things:

Is there specific information available for understanding how the body is affected by long-term thyroidectomy?

Is there specific information regarding mid-life hormonal changes in women and how that might affect thyroxine absorption and requirement, particularly in someone who has had a thyroidectomy? I find a lot on information on hypothyroidism and decreased function in mid-life, but because I don’t have a thyroid, none of that quite applies. Any help would be greatly appreciate as I am currently working only with a GP and am not yet at the stage for an endocrinologist referral. Daniela, Toronto ON

Dr. Morrison:The approach of the Family Doctor to increase the dose to normalize the TSH is appropriate. Levothyroxine requirements can change due to changes in absorption (usually eating at the same time as taking, or taking other meds/vitamins at the same time as levothyroxine), changes in weight (weight gain may increase requirement, loss decrease), changes in estrogen levels (more estrogen, like oral contraceptive pills and pregnancy, increase requirements; less estrogen, like menopause, decreases requirements. The timing of development of hypothyroidism/thyroidectomy is probably not relevant.

The next section is of very rare situations and should only be considered if increasing the dose or identifying a cause of impaired absorption does not solve the issue, or if the FT4 goes above the normal range but TSH remains elevated.

Rarely (outside of impairing absorption) drug interactions can affect the metabolism of thyroid hormones. TSH levels can very be falsely elevated by interfering substances in a patient’s blood, e.g. heterophile antibodies, rheumatoid factor or the presence of inactive macroTSH.

(TB Autumn 2020)

I would like to know what could be the impact of taking soy milk when a person takes Synthroid?

Dr. Morrison:  Many foods can interfere with absorption of thyroid hormone (e.g. Synthroid or Eltroxin). It is ideal to take thyroid hormone at least four hours after taking soy, dairy, calcium supplements/antacids, iron supplements; probably also best to wait about an hour before eating, but the most important thing is to take at the same time, and in the same way each day, the time of day is not important as long as there is consistency.

If the Synthroid has always been taken a few minutes before the intake of milk, and the TSH is normal, should we still wait 30 min before taking the milk / calcium?  Or is there a risk of TSH dosing being disrupted and medication adjustment necessary?

Dr. Morrison:  Consistency is most important, if someone was just starting thyroid hormone replacement I’d advise not to take with dairy, as above, but if this has been a steady routine and TSH is normal I would not change anything. If one decided to stop drinking the milk for some other reason, then a TSH should be checked in about 6 weeks to see if a dose reduction would be necessary.

What other possible causes can there be for the drop in TSH to 0.21, in a 52-year-old woman, in good health, without any other comorbidities, complying with her medication, physically active, with healthy eating habits ?

Dr. Morrison:  Changes in thyroid hormone requirements are most often due to changes in absorption. This can be due to variations in how the medication is taken (with and without food, missing doses, extra doses), or how changes in the gut (acid levels – e.g. taking antacid drugs not only can bind the thyroid hormone, but could change the stomach acid environment and have an effect on absorption). Gut diseases like celiac, inflammatory bowel diseases and other causes of malabsorption could cause an increase in thyroid hormone requirements; fixing any off these things could cause a decrease in dose requirement.

Changes in weight can effect the amount of thyroid hormone needed; increase in weight might result in increased dose requirement, vice versa for weight loss.

Changes in thyroid hormone binding protein levels can effect the need for thyroid hormone.  E.g. estrogen level changes, more estrogen (pregnancy, birth control pill, hormone replacement therapy) means more thyroid hormone binding proteins, less free (active) thyroid hormone, and a need for increased thyroid hormone dose.  Less estrogen (e.g. menopause), means less thyroid protein binding proteins and that could mean a need for a dose reduction – this could be what is going on in this case.

Rarely something can interfere with the accuracy of the TSH, taking high dose biotin can falsely lower TSH; the TSH should be repeated about a week after stopping biotin.  Very rarely some people have antibodies in their blood that interfere with TSH testing and usually this would cause falsely high levels; this is very uncommon.

(TB Spring 2021)

I live in BC, and I was diagnosed with Hashimoto’s after the birth of my third child 30 years ago. I was stable for years, but about 20 years ago, when I was about 50, I began to experience symptoms. For about 10 years, my levels went up and down as my doctor adjusted my Synthroid dose according to my symptoms. Finally, I heard about a doctor in Victoria, an endocrinologist specializing in thyroid problems, and my doctor kindly referred me to him. He ordered free T3 & T4, and based on the results, prescribed SR liothyronine in addition to Synthroid. My symptoms improved dramatically. I live in a small, remote coastal town (Powell River), and no one here had heard of prescribing liothyronine in addition to thyroxine for some patients, and there was frank skepticism. However, I’ve continued to do much better than I was doing before seeing the endocrinologist, though I still have some trouble keeping both levels near target. Also, I find that it can be difficult to get blood work done, as some labs won’t do free T3 & T4 and do a TSH instead, even if the requisition is clear.

I know this was controversial some years ago; I don’t know if that’s still the case. But I wonder if it’s a topic you might think worth addressing at some point. I now wonder if my mother, who also was hypothyroid (as are my sister & brother) might not have been like me, needing liothyronine to help keep her free of symptoms. When I look back at how she was, I remember her as being overweight, tired, constipated, irritable, brittle nails, thinning hair, all things that alsoaccompany age, but I do wonder if perhaps she was like me, and how much easier her life might have been if she’d been adequately replaced, assuming she wasn’t.

I don’t know how many thyroid patients are taking liothyronine. According to the literature I was given, about 20 per cent of us do better with it. I wonder if there are other people who are like I was before I began taking liothyronine, when I was symptomatic and swinging between high and low as my doctor adjusted my Synthroid prescription up and down.

Thank you for any perspective you can offer,</p/>Madeleine F., Powell River BC

Dr. Morrison:  For a large majority of people with hypothyroidism levothyroxine treatment is effective. Unfortunately, a minority ofpeople with hypothyroidism have persistent symptoms despite what seems to be optimal levothyroxine therapy. Itis not yet clear whether combination treatment might help some of these patients. Large high quality randomisedcontrolled trials are needed to address this question. In the meantime for some people with hypothyroidism,after excluding other causes for symptoms, a trial of combination therapy is reasonable with an appropriate dosecombination of T4 and T3, and careful monitoring of thyroid function tests and symptoms.

(TB Spring 2020)

Dr. Morrison:  The recommendation for monitoring and adjusting treatment for primary hypothyroidism is to check TSH ~6-8 weeks after a dose adjustment and periodically (e.g. ~ yearly) when stable. Monitoring the FT4 and FT3 is not necessary unless there is one of the rare situations where the TSH is thought to be inaccurate (i.e. due to laboratory assay interference) or there is high suspicion for pituitary disease.

The FT4 and FT3 are not necessary and may be more affected by when the last dose was taken.

Most people can achieve a stable TSH if the levothyroxine is taken on an empty stomach around the same time each day with no major changes to weight or health.

Dr. Morrison:  The most common reason for Hashimoto’s to flare up is post pregnancy; this is called post-partum thyroiditis.  The immune system is relatively suppressed during pregnancy and the concentration of antibodies that cause Hashimoto’s often decreases, after delivery there is a relative flare of antibodies that can cause sudden thyroid inflammation resulting in leaking out of preformed thyroid hormone, and temporary hyperthyroidism, followed by returning to normal, or a period of hypothyroidism.  While the thyroid usually recovers, sometimes a person might remain hypothyroid long term after post-partum thyroiditis.  Outside of the post-partum period the hyperthyroid phase of Hashimoto’s is uncommon, but can occur, it is not well understood what else contributes to these rare flares or influences changes in antibody concentrations.

Dr. Morrison:  There does seem to be some association between higher TSH levels in cold weather in people with working thyroids.  The season/weather would not be expected to change thyroid blood test results in people taking thyroid hormone replacement, as far as I know.

Dr. Morrison:  I don’t know of a reason that the surgery would have a longstanding impact on thyroid hormone levels.  For people taking thyroid hormone replacement reasons for a change in requirement can be weight changes, or a change in estrogen levels.  Weight gain may result in need of a higher dose, weight loss might require a lower dose.  Higher estrogen states (pregnancy, hormonal contraception, pre-menopause) may require higher levothyroxine doses compared with lower estrogen states.

Dr. Morrison:  Severe, prolonged, and untreated hypothyroidism could decrease pulse and blood flow output from the heart and possibly cause congestive heart failure, but usually even then only if another severe illness occurs simultaneously as a stress on the system.

 Long term and significant overtreatment of Hashimoto’s with much higher than necessary doses of thyroid hormone replacement could cause a cardiomyopathy due to sustained, abnormal high pulse rate, but this would be easily avoided with appropriate dosing and periodic monitoring of the TSH.