Final answer:
Low levels of serotonin are most closely linked to depression.
Step-by-step explanation:
Under supply of serotonin is most closely linked to c) Depression.
Serotonin, also known as 5-hydroxytryptamine (5-HT), is a neurotransmitter that plays a crucial role in mood regulation. Low levels of serotonin have been consistently associated with depression, as serotonin helps regulate feelings of happiness and well-being. Decreased serotonin levels can lead to symptoms such as sadness, loss of pleasure, changes in appetite and sleep patterns, difficulty concentrating, and thoughts of worthlessness.