Is it true that eating broccoli can interfere with levothyroxine absorption or thyroid function, and should I change how I time my dose if I eat it?

Eating broccoli does not specifically block levothyroxine absorption, but meals in general can reduce levothyroxine uptake if the tablet is taken too close to food; you do not need to avoid broccoli, but you should take levothyroxine on an empty stomach and separate it from meals and certain supplements. ^{[1] [2]}

Key points at a glance

• Levothyroxine is absorbed best on an empty stomach; food can lower or delay its absorption and make TSH levels more variable. ^{[2] [3]}
• Official guidance advises taking levothyroxine once daily, on an empty stomach, 30–60 minutes before breakfast, and at least 4 hours apart from interacting medications/supplements. ^{[2] [4]}
• Broccoli and other cruciferous vegetables do not appear to impair thyroid function in typical cooked servings among iodine‑sufficient people, and there is no direct evidence they uniquely reduce levothyroxine absorption. ^[5]
• Some foods and supplements clearly reduce levothyroxine absorption (e.g., soybean flour, high‑fiber binders, walnuts; and minerals like calcium or iron), so consistent timing and spacing are important. ^{[6] [7]}

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Levothyroxine and food: what matters

Levothyroxine’s absorption is sensitive to the presence of food, which can decrease or delay how much medicine gets into your system. ^[2] This is why labels recommend taking it on an empty stomach, 30–60 minutes before breakfast, and maintaining a consistent routine day to day. ^[2] In clinical studies, taking levothyroxine with breakfast or at bedtime (vs. fasting) led to higher and more variable TSH levels, indicating less predictable absorption. ^[3]

Certain foods and supplements are known to bind levothyroxine and reduce absorption, including soybean flour, cottonseed meal, walnuts, and dietary fiber; minerals such as calcium and iron, antacids containing aluminum or magnesium, bile acid sequestrants, phosphate binders, and others can also interfere and should be separated by several hours. ^{[6] [7]} Guidance advises keeping at least a 4‑hour gap from drugs known to interfere with levothyroxine absorption. ^[1]

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Broccoli and cruciferous vegetables

Cruciferous vegetables (such as broccoli, Brussels sprouts, kale, cabbage) contain natural compounds (glucosinolates) that can form “goitrogens,” but cooking inactivates key enzymes and typical dietary amounts have not shown harmful effects on thyroid hormone levels in humans with adequate iodine intake. ^[5] In a small human study, eating 150 g of cooked Brussels sprouts daily for 4 weeks did not change TSH, T4, or T3. ^[5]

Importantly, levothyroxine product information and clinical guidance do not list broccoli specifically as a food that binds levothyroxine or requires special timing beyond the standard empty‑stomach recommendation. ^[2] Therefore, there is no evidence that broccoli uniquely impairs levothyroxine absorption when compared with other ordinary foods. ^[2]

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How to time your dose if you eat broccoli

• Keep doing the standard, evidence‑based timing: take levothyroxine with water on an empty stomach, 30–60 minutes before breakfast. ^[2]
• If you prefer evening dosing, take it at least 3–4 hours after your last meal to mimic an empty stomach, and be consistent with the schedule. ^[1]
• You do not need to avoid broccoli; just avoid taking your tablet with food (including broccoli) and keep your dosing routine consistent. ^[2]
• Always separate levothyroxine by at least 4 hours from calcium or iron supplements, certain antacids, or bile acid sequestrants, which are proven to interfere. ^{[7] [1]}

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Practical examples

• Morning routine: Take levothyroxine with water when you wake up, wait 30–60 minutes, then have breakfast (broccoli omelet included if you like). ^[2]
• Evening routine: Eat dinner (with broccoli if desired), wait 3–4 hours with no further food or supplements, then take levothyroxine before bed. ^[1]
• Supplements: If you take calcium or iron, schedule them at lunch or bedtime if you dose levothyroxine in the morning, maintaining a 4‑hour gap. ^[7]

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When to consider adjustments

If your TSH results become unexpectedly high or variable after changing your meal timing, coffee habits, fiber intake, or supplement schedule, it may suggest altered absorption and your dose or timing may need to be adjusted. ^[3] Keeping a consistent pattern around dosing usually minimizes the need for changes. ^[2]

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Quick reference table

Topic	What to do	Why
Empty stomach dosing	Take 30–60 min before breakfast or 3–4 hours after the last meal	Food can reduce/delay absorption and raise TSH variability. [2] [3]
Broccoli/crucifers	No avoidance needed; just don’t take with food	Typical servings, especially cooked, have not shown harm to thyroid function. [5]
Calcium/iron/antacids	Separate by ≥4 hours	These agents bind levothyroxine and impair absorption. [7] [1]
Consistency	Keep the same routine daily	Consistent timing improves stable TSH control. [2]

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Bottom line

You don’t need to stop eating broccoli. Focus on taking levothyroxine on an empty stomach and keeping a consistent schedule, and keep a clear 4‑hour gap from minerals like calcium and iron or other known binding agents. ^{[2] [7]} If labs shift after a change in your routine, your clinician may fine‑tune the dose or timing. ^[3]