How to avoid food-drug interaction

Dear Dr. Roach: I’ve been taking levothyroxine for 30 years. I take my daily dosage at about 4 a.m. and eat breakfast at 6:30, more or less.

I usually have the same breakfast: rolled oats with some flax meal, blueberries, pea milk and half a banana. I just read an article in the newspaper that says I should wait four hours before eating any potassium-rich food, like a banana. Am I in danger?

J.S.B.

Answer: High potassium foods like bananas are a potential concern for people taking medications that raise the body’s potassium level. This would include ACE inhibitors (lisinopril and any other blood-pressure medicine ending in “-pril”), angiotensin receptor blockers (whose generic names all end in “-sartan”), some specific diuretics (such as spironolactone and triamterene), and of course potassium itself.

Thyroid medication absorption can be blocked by calcium or iron, or by foods very high in these, including milk and most plant-based milk substitutes like your pea milk (some studies show reduction in absorption by coffee as well).

When taken together, calcium can block absorption of thyroxine by 8%, which may be enough to make a normal thyroid hormone level become abnormal.

However, you are taking your calcium well after the thyroid medication, and I doubt there is much reduction in your thyroid hormone absorption, if any, from not taking calcium at all.

More importantly, your thyroid dose has been adjusted to the way you take your medication related to eating. Making a change now might require your dose to be adjusted.

Consistency is the key here: I recommend against changing your preferred breakfast or when you take medication.

This advice is good for many medicines. Warfarin (Coumadin), for instance, blocks vitamin K and prevents the body from making clotting factors. People should eat the same amount of vitamin K containing foods (especially dark greens) every day. So for a person on warfarin, stopping your daily spinach salad could make your meds work too well.