Drug Name: Thyrolar

Nutritional Considerations

• Ingestion of soy products simultaneously with thyroid hormones appears to reduce the absorption of the hormones.

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• To be safe, people taking thyroid medication should not consume soy products within three hours of taking their medication. In addition, infants with congenital hypothyroidism given thyroid medication must not be given increased or reduced amounts of soy-based formula without consulting a pediatrician or pediatric endocrinologist.

  1. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in infants with congenital hypothyroidism: The influence of soy-based formulas. J Am Coll Nutr 1997;16:280—2

• Calcium supplementation should be separated by at least four hours from the taking of this medication.

  1. Schneyer CR. Calcium carbonate and reduction of levothyroxine efficacy. JAMA 1998;279:750.
  2. Singh N, Singh PN, Hershman JM. Effect of calcium carbonate on the absorption of levothyroxine. JAMA 2000;283:2822-5.

• Iron deficiency may result in the body's inability to produce thyroid hormones. Ask your physician if you have an iron deficiency. Supplementation of this mineral may help your body in its normal thyroid function, particularly if you are on a restricted or low calorie diet.

  1. Beard JL, Borel MJ, Derr J. Impaired thermoregulation and thyroid function in iron deficiency anemia. Am J Clin Nutr 1990;52:813-9.
  2. Beard J, Borel M, Peterson FJ. Changes in iron status during weight loss with very-low-energy diets. Am J Clin Nutr 1997;66:104-10.
  3. Campbell NR, Hasinoff BB, Stalts H, et al. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Intern Med 1992;117:1010-3.
  4. Campbell NR, Hasinoff BB. Iron supplements: A common cause of drug interactions. Brit J Clin Pharmacol 1991;31:251-5.

• Thyroid hormone medications taken with food may result in a decrease absorption of the medication. Separate taking this medication by at least two hours from foods.

  1. Liel Y, Harman-Boehm I, Shany S. Evidence for a clinically important adverse effect of fiber-enriched diet on the bioavailability of levothyroxine in adult hypothyroid patients. J Clin Endocrinol Metab 1996;81:857-9.
  2. Threlkeld DS, ed. Hormones, Thyroid Hormones. In Facts and Comparisons Drug Information. St. Louis, MO: Facts and Comparisons, Jun 1991, 132-3c.