This is the 11242nd most frequent Portuguese word.
melatonina
Melatonina: A hormone that regulates sleep-wake cycles.
In this sentence, 'melatonina' refers to the hormone that plays a role in controlling sleep cycles.
A melatonina ajuda a regular o sono.
Melatonin helps regulate sleep.
Here, 'melatonina' is used in the context of dietary supplements containing the hormone to aid sleep.
Você já experimentou um suplemento de melatonina?
Have you ever tried a melatonin supplement?
In this case, 'melatonina' describes the subject of scientific studies and research related to its effects.