Ask the Doctor

Dr. Deric Morrison, Endocrinologist, answers your questions.

Dr. Deric Morrison, MD FRCPC, ECNU
Medical Advisor to the Thyroid Foundation of Canada


 

Childhood thyroidectomy and mid-life changes

I had a full thyroidectomy at the age of 13 and of course have been on thyroid replacement since then. Now at the age of 44 I’m currently, rather suddenly in the past months, experiencing a very high TSH level and starting the road of adjusting meds … 

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I had a full thyroidectomy at the age of 13 and of course have been on thyroid replacement since then. Now at the age of 44 I’m currently, rather suddenly in the past months, experiencing a very high TSH level and starting the road of adjusting meds to see if I’m responsive to this sudden change. I thought I might have had an interaction with a new supplement, but after a 4–5 week bloodwork follow-up after stopping the supplement, my TSH has budged only slightly from 9 to 8.85. This is highly irregular for me.

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 patients blood, e.g. heterophile antibodies, rheumatoid factor or the presence of inactive macroTSH.

Thyroid and soy products:

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

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

Dr. MorrisonMany 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.

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