The only two items I can see research done to confirm that when ingested close to Levo dosing cause issues with taking Levo are dairy/milk/caffeine or coffee.
Two questions:
Are there any other items that cause the same amount of issues in this way
Why is there confidence that keeping outside of a certain time limit makes them OK eg take your coffee one hour before Levo dose
Any feedback appreciated
Just to be clear .. coffee etc 1 hour before levo ... not ok .
For optimal absorption Levo Should be taken on empty stomach .
Coffee etc 1 hour after levo is ok because levo has then had an hour in ideal conditions to be absorbed (before coffee etc gets there)
This paper has lots of detailed info on the subject of Gastrointestinal Malabsorption of Thyroxine .
academic.oup.com/edrv/artic...
".......The tablet formulations of levothyroxine contain a stable salt, sodium T4, together with a variety of excipients (27). After ingestion, a dissolution phase of the tablet is necessary for the subsequent intestinal absorption and, in the dissolution phase, a near physiologic gastric pH is required (28). After dissolution, and disregarding a hypothetical minimal absorption in the stomach, T4 is essentially absorbed in the small intestine (29, 30).
Wenzel and Kirschsieper (31) showed that the absorption of T4 is significantly reduced when the drug is taken after a meal. Indeed, it has been shown that certain foods or drinks (e.g., dietary fibers, soybeans, coffee, or papaya) (32–35) reduce the absorption of T4. Additionally, nonfasting regimens of T4 administration are associated with higher and more variable serum TSH concentrations (36).
Under fasting conditions (in euthyroid subjects), the unidirectional absorption of T4 or peak values of T4 absorption occur in the first 90 minutes following T4 administration, with a rapid increase in the first 60 minutes (37). The time to reach the maximum concentration (Tmax) of T4 is ∼2 hours after T4 ingestion. Shortly afterward, absorption starts to plateau (37, 38). On average, 60% to 80% of ingested T4 is absorbed and rendered bioavailable, with the distribution volume of the hormone averaging 11.5 L (37). However, in a study on hypothyroid subjects the Tmax and distribution volumes were 3 hours and ∼15 L, respectively (38). After a meal, the peak value of T4 absorption is decreased and Tmax is delayed, with resulting decreased T4 bioavailability.
When food is not postponed by at least 1 hour following T4 ingestion, delayed and decreased intestinal absorption of T4 may follow (37). However, bedtime intake of T4 significantly improved thyroid hormone efficacy, probably because the lower intestinal motility at night increases the exposure time of T4 to the intestinal mucosa (39) or because of better patient compliance with the treatment (40).
Based on these results, postponing breakfast by 1 hour after ingestion of T4 has been suggested in different studies (28, 36, 40) to warrant efficient absorption of T4 and to carry out proper studies on malabsorption (41). In fact, in the latter studies the daily dose of T4 required to obtain a serum TSH between 0.5 and 2.5 mU/L was 1.3 μg/kg body weight (42, 43). This dose is significantly lower than the one recommended by an ad hoc American Thyroid Association task force (1.6 to 1.8 μg/kg body weight) in adult patients with minimal endogenous thyroid function (4).
Despite these studies, leaflets on this hormone still indicate a lag time of 30 minutes between the morning ingestion of T4 and breakfast, and the same interval is commonly recommended by the prescribing physicians. Weekly tablet T4 administration has also been proposed (44), suggesting that autoregulatory mechanisms may maintain near-euthyroidism. However, for complete biochemical euthyroidism, a slightly larger dose than sevenfold the normal daily dose may be required (44). Presently, weekly tablet T4 administration is used only to detect nonadherence to treatment....."
If there is a long enough gap, the levothyroxine is unlikely to come into contact with the food/drink/supplements in question.
This is the issue which is addressed by a time limit. Although some people have extreme delayed gastric emptying/gastroparesis, for most of us, a couple of hours are enough.
If the interaction occurs in our bloodstreams, or elsewhere, the suggested time gaps would not be useful.
When the interaction with iron (e.g. ferrous sulfate) was first being discussed in papers, they found that there could be an impact up to four hours away.
Even NHS website says avoid calcium rich foods (eg milk, butter) for 4 hours after levothyroxine
Many people find it better to take levothyroxine at bedtime
Many thanks for the responses - I take.note of the advice not to take Levo after a meal
Is it okay to cycle my Levo dose? 
symptoms when increasing levo dose
Foods that react with Levo 
Increasing Levo Dose 
25mcg levo dose increase
