Levothyroxine absorption and food interactions
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Levothyroxine Absorption and Food Interactions
Impact of Food and Beverages on Levothyroxine Absorption
Levothyroxine absorption is significantly affected by the presence of food and certain beverages. Taking levothyroxine with meals, especially those high in fiber, soy, or iodine, can decrease its absorption and reduce its effectiveness in treating hypothyroidism 12479. Coffee, soy products, dietary fiber, and enteral nutrition have all been shown to lower levothyroxine absorption when taken together with the medication 1249.
Specific Food Interactions: Milk, Coffee, and Juices
Cow’s milk, which contains a high amount of elemental calcium, has been shown to significantly reduce the absorption of levothyroxine when ingested at the same time 145. Coffee and certain juices, such as grapefruit juice, can also interfere with levothyroxine absorption, though the effect of grapefruit juice appears to be minor and may only slightly delay absorption without major clinical impact 1489.
Dietary Supplements and Mineral Interactions
Calcium and iron supplements are well-documented to decrease levothyroxine absorption due to direct complexing with the drug in the gut 1234. Other supplements and medications, such as aluminum-containing antacids, phosphate binders, and chromium supplements, can also impair absorption 1234.
Soy Products and Levothyroxine
The evidence regarding soy products is mixed. While some case reports suggest a possible reduction in absorption with soy, larger and more controlled studies have not consistently shown a significant effect, especially with newer liquid formulations of levothyroxine 1410. The clinical impact of soy on levothyroxine absorption appears to be limited .
Timing and Formulation: Strategies to Improve Absorption
To maximize absorption, it is generally recommended to take levothyroxine on an empty stomach, ideally 30–60 minutes before breakfast or at bedtime, several hours after the last meal 1246. Maintaining a proper time interval between levothyroxine and food or supplements, especially coffee, calcium, and iron, is an effective way to avoid interactions 124.
Newer formulations, such as liquid solutions and soft-gel capsules, may help reduce the impact of food and supplement interactions, offering more flexibility in dosing and potentially improving absorption even when taken closer to meals 1269. For example, a novel levothyroxine solution has shown comparable absorption when taken 10 or 30 minutes before a high-fat, high-calorie breakfast, suggesting that the interval before eating may be shortened with these formulations .
Enhancers of Levothyroxine Absorption
Vitamin C has been observed to enhance levothyroxine absorption, though more research is needed to confirm this effect and its clinical significance 14.
Conclusion
Levothyroxine absorption is highly sensitive to food, beverages, and dietary supplements, with many common items—such as milk, coffee, fiber, calcium, and iron—reducing its effectiveness if taken together. The best practice is to take levothyroxine on an empty stomach and to separate it from interfering foods and supplements by at least 30–60 minutes. Newer liquid and soft-gel formulations may offer improved flexibility and absorption, even when taken closer to meals. Patients and clinicians should be aware of these interactions to ensure optimal management of hypothyroidism.
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