L-thyroxine malabsorption due to calcium carbonate impairs blood pressure, total cholesterolemia, and fasting glycemia

[helvella]

Suggestions to separate taking levothyroxine from medicines/supplements is very frequent on this forum.

And, yet again, backed up by research.

These women will not have decided on their own, "let us take calcium carbonate after levothyroxine". No, of course not. Some medic, somewhere, will have suggested, advised, maybe prescribed the supplement. And (obviously) failed to make sure the patients understand the need to separate such things from levothyroxine.

Mind, that their conclusion has to speak of not "solely measuring serum TSH" indicates something about their expected audience.

Endocrine. 2019 May;64(2):284-292. doi: 10.1007/s12020-018-1798-7. Epub 2018 Oct 27.

L-thyroxine malabsorption due to calcium carbonate impairs blood pressure, total cholesterolemia, and fasting glycemia.

Morini E1, Catalano A1, Lasco A1, Morabito N1, Benvenga S2,3,4.

Author information

1 Department of Clinical and Experimental Medicine, University of Messina, Messina, Italy.

2 Department of Clinical and Experimental Medicine, University of Messina, Messina, Italy. [e-mail].

3 Master Program on Childhood, Adolescent and Women's Endocrine Health, University of Messina, Viale Gazzi, 98125, Messina, Italy. [e-mail].

4 Interdepartmental Program of Molecular & Clinical Endocrinology, and Women's Endocrine Health, University Hospital Policlinico G. Martino, Messina, Italy. [e-mail].

Abstract

PURPOSE:

Calcium carbonate was previously shown to interfere with L-thyroxine absorption. To estimate the magnitude of tablet L-thyroxine malabsorption caused by calcium carbonate, with resulting increase in serum thyrotropin (TSH), we performed a cohort study in a referral care center.

METHODS:

Fifty postmenopausal hypothyroid L-thyroxine-treated women (age 71.7 ± 5.1 years) who added calcium supplementation (600-1000 mg/day) were considered. They were taking L-thyroxine 45-60 min before breakfast (setting 1). After 4.4 ± 2.0 years from initiation of L-thyroxine therapy, they took calcium supplemaentation within 2 h after L-thyroxine taking (setting 2) for 2.3 ± 1.1 years. Hence, we recommended postponing calcium intake 6-8 h after L-thyroxine (setting 3). We evaluated TSH levels, the prevalence of women with elevated TSH (>4.12 mU/L), total cholesterolemia, fasting glycemia, blood pressure, and the prevalence of hypercholesterolemia, hyperglycemia, and hypertension.

RESULTS:

TSH levels were 3.33 ± 1.93 mU/L versus 1.93 ± 0.51 or 2.16 ± 0.54 comparing setting 2 with setting 1 or 3 (P<0.001, both). In setting 2, 18% women had elevated TSH versus none in setting 1 or 3 (P<0.01). Total cholesterolemia, fasting glycemia, systolic, and diastolic blood pressure were also significantly higher in setting 2 compared to settings 1 and 3. For every 1.0 mU/L increase within the TSH range of 0.85-6.9 mU/L, total cholesterolemia, glycemia, systolic, and diastolic blood pressure increased by 12.1, 3.12 mg/dL, 2.31, and 2.0 mmHg, respectively.

CONCLUSIONS:

Monitoring of hypothyroid patients who ingest medications that decrease L-thyroxine absorption should not be restricted to solely measuring serum TSH.

KEYWORDS:

Blood pressure; Calcium carbonate; Fasting blood glucose; Hypothyroidism; L-thyroxine malabsorption; Serum cholesterol

PMID: 30368654

DOI: 10.1007/s12020-018-1798-7

ncbi.nlm.nih.gov/pubmed/303...

[SlowDragon Administrator]

NHS website warns of interactions of various foods and medicines with levothyroxine....but of course most medics won’t have read that or advise patients

nhs.uk/medicines/levothyrox...

There are some foods and drinks that don't mix well with levothyroxine.

Drinks containing caffeine, like coffee, tea and some fizzy drinks, can reduce the amount of levothyroxine your body takes in. Leave at least 30 minutes after taking levothyroxine before you drink them.

Calcium-rich foods, such as milk, cheese, yoghurt and broccoli, can reduce the amount of levothyroxine your body takes in. Leave at least 4 hours between taking levothyroxine and eating calcium-rich foods.

Soya in food and supplements may stop levothyroxine working properly. If you regularly eat soya or take soya supplements your doctor might need to do extra blood tests to make sure you're getting enough levothyroxine.

Kelp (a type of seaweed) can contain high levels of iodine, which sometimes makes an underactive thyroid worse. Do not take supplements containing kelp if you're taking levothyroxine.

[helvella Administrator Thyroid UK in reply to SlowDragon]

The way that is written allows you to think of coffee as being a "wait 30 minutes" drink - and completely ignore or miss the four hours needed for mega-latte or cappuccino grande with lots of calcium-rich milk. Or soya milk.

[asiatic]

I believe calcium carbonate is used as a filler in many tablets eg. Atorvastatin. I suppose the amounts being so small are not significant.

[helvella Administrator Thyroid UK]

How do the flagging systems get designed, maintained and updated?

I suspect that any new interaction of this nature would take quite some time to be noticed and filter through into these systems.

And without having access, we cannot check.

[helvella Administrator Thyroid UK]

You are quite right - I was just calling into question all such systems with a specific example of how we would positively expect them to be wrong.

We have no idea, other than guesswork, how any of these systems were developed. Could they have missed some really obvious examples?

I'll give you one specific example/question. Many levothyroxine documents were updated to show that there is an interaction between levothyroxine and ferrous sulphate. But everyone continued to ignore ferrous fumarate, sodium feredetate, ferrous gluconate, ferric maltol, even liver!

(Those are just some of the prescription iron products, leaving aside the "supplements" so many find they have to buy.)

I suggest that the MHRA should have an accessible database and a system which parallels the Yellow Card system. You or I should be able to look up current known status, and any ongoing questions/research. If we think some issue is missing, we fill in a form.

There are all too many combinations which might never have been tested together and any suspicions could be important.

I have wondered whether anyone has ever tested carbimazole and levothyroxine together? I could easily imagine that if you had suggested it years ago, you would have been laughed out of court. Obviously no-one would take both at the same time so no possible issue. Until another person dreamt up block-and-replace.

[helvella Administrator Thyroid UK]

I'd go so far as to say that we should be able to look up, for example, levothyroxine and "eye of newt". And see "No research has been performed" - not just be unable to find it!

(Obviously joking - but seems not unreasonable to include all prescription medicines and well-known supplements.)