Registered Practical Nurse (RPN) Practice Test

Serotonin levels are influenced by fluctuations in dietary intake of what substance?

1. Tyrosine

2. Glutamine

3. Tryptophan

4. Phenylalanine

The correct answer is: Tryptophan

Serotonin is a neurotransmitter that plays a significant role in mood regulation, among other functions in the body. Its synthesis in the body is closely linked to the availability of certain dietary components, with tryptophan being the most critical. Tryptophan is an essential amino acid, which means that the body cannot produce it on its own and must obtain it from dietary sources. Once ingested, tryptophan undergoes conversion into serotonin through a series of biochemical reactions, which are also influenced by the presence of other nutrients, particularly carbohydrates. When dietary intake of carbohydrates increases, it helps to increase the transport of tryptophan across the blood-brain barrier, thereby enhancing serotonin production. The other options—tyrosine, glutamine, and phenylalanine—are also amino acids, but they are primarily involved in the production of different neurotransmitters. Tyrosine is a precursor for dopamine and norepinephrine, glutamine serves various roles including as a neurotransmitter itself, and phenylalanine can also be converted into tyrosine. While these compounds play essential roles in the body, they do not have the same direct influence on serotonin synthesis as tryptophan does. Thus,