L-thyroxine malabsorption due to calcium carbonate impairs blood pressure, total cholesterolemia, and fasting glycemia
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.
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In 50 postmenopausal women with L-T4-treated primary hypothyroidism who started taking 600-1000 mg/d calcium carbonate ≤2 h after L-T4, undertreated hypothyroidism (TSH >4.12 mU/L) occurred in 9/50 women (18%); overall TSH increased from 1.93 ± 0.51 to 3.33 ± 1.93 mU/L (+73%), but when all women took calcium 6-8 h after L-T4, all had TSH <4.12 mU/L (2.16 ± 0.54 mU/L).
“Fifty postmenopausal women with L-T4-treated PH started taking 600–1000 mg/d calcium carbonate ≤2 h after L-T4. UTH (TSH >4.12 mU/L) occurred in 9/50 women (18%). Overall, TSH increased from 1.93 ± 0.51 mU/L to 3.33 ± 1.93 mU/L (+73%), but when all women took calcium 6–8 h after L-T4, all had TSH <4.12 mU/L (2.16 ± 0.54 mU/L) (44).”
From L-T4 therapy in the presence of pharmacological interferents (2020) · cites this paper as [44]
Concerning interfering medication-induced undertreated hypothyroidism, few data are available on metabolic/cardiovascular complications and costs of frequent assays to monitor L-T4 therapy.
“Concerning IM-induced UTH, few data are available on two issues (23, 44, 98, 99): (i) metabolic/cardiovascular complications, (ii) costs of frequent assays to monitor L-T4 therapy.”
From L-T4 therapy in the presence of pharmacological interferents (2020) · cites this paper as [44]
For every 1.0 mU/L increase within the TSH range of 0.85-6.9 mU/L, total cholesterolemia, fasting glycemia, systolic blood pressure, and diastolic blood pressure increased by 12.1 mg/dl, 3.12 mg/dL, 2.31 mmHg, and 2.0 mmHg, respectively.
“For every 1.0 mU/L increase within the TSH range of 0.85–6.9 mU/L, TC, FG, SBP, and DBP increased by 12.1 mg/dl, 3.12 mg/dL, 2.31 mmHg, and 2.0 mmHg, respectively (44).”
From L-T4 therapy in the presence of pharmacological interferents (2020) · cites this paper as [44]
In 50 postmenopausal L-T4-treated primary hypothyroidism women, TSH increased significantly from 1.93 ± 0.51 (before calcium; setting 1) to 3.33 ± 1.93 mU/L (calcium taken ≤2 h after L-T4; setting 2), and was significantly lower than 2.16 ± 0.54 mU/L (calcium taken 6-8 h after L-T4; setting 3); total cholesterolemia, fasting glycemia, systolic and diastolic blood pressure were also significantly
“In the above study on 50 postmenopausal L-T4-treated PH women (44), TSH increased significantly from 1.93 ± 0.51 (before calcium; setting 1) to 3.33 ± 1.93 mU/L (calcium taken ≤2 h after L-T4; setting 2), and was significantly lower than 2.16 ± 0.54 mU/L (calcium taken 6–8 h after L-T4; setting 3). Total cholesterolemia (TC), fasting glycemia (FG), systolic and diastolic blood pressure (SBP and D”
From L-T4 therapy in the presence of pharmacological interferents (2020) · cites this paper as [44]
Regular intake of 600 to 1000 mg calcium carbonate near levothyroxine can raise TSH, with the effect lessening as the interval between them increases.
“Regular consumption of 600 to 1000 mg of calcium carbonate near the time of taking LT4 can elevate TSH levels, although this situation diminishes as the time interval between them increases.34,52”
From Refractory hypothyroidism: unraveling the complexities of diagnosis and management (2023) · cites this paper as [52]
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References 47 · Cited by 12
- Authors
- Morini, E., Catalano, A., Lasco, A., Morabito, N., & Benvenga, S.
- Affiliations
- University of Messina (IT)
- Corresponding author
- Benvenga, Salvatore
- Venue
- Endocrine
- Published
- 2018-10-27
- Volume
- 64
- Issue
- 2
- Pages
- 284-292
- ISSN
- 0969-711X (ISSN-L)
- 1355-008X
- 1559-0100
- OpenAlex
- W2898302663
- Cited by
- 12
- References
- 47
- Citations by year
- 2026: 1 · 2024: 1 · 2023: 2 · 2022: 1 · 2021: 3 · 2020: 1 · 2019: 3
- FWCI
- 1.39
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- www.springer.com/tdm (tdm)
- Locations
- Endocrine (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
- Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
- Health Sciences › Medicine › Nephrology › Parathyroid Disorders and Treatments
- Keywords
- levothyroxine, calcium carbonate, drug malabsorption, hypothyroidism, thyroid-stimulating hormone, hypercholesterolemia, hyperglycemia, hypertension, postmenopausal women
- MeSH terms
- Aged, Blood Glucose, Blood Pressure, Calcium Carbonate, Cholesterol, Fasting, Female, Humans, Hypothyroidism, Thyroid Hormones, Thyrotropin, Thyroxine, Dietary Supplements
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