A vitamin is an organic compound required as a nutrient by a living organism. It was not unusual for humanoids to crave foods that were rich in the very vitamins and minerals that their bodies were lacking. (VOY: "Elogium")
According to a commercial for the cereal Tribbles, it came with eighteen essential vitamins. (ST: "The Trouble with Edward", credit cookie)
In 2267, Doctor McCoy suggested that Montgomery Scott simply needed to take some vitamins before he saw how he, like much of the crew, was undergoing accelerated aging. (TOS: "The Deadly Years") Three years later, following McCoy's acquittal from charges stemming from the outbreak of a plague the Dramens believed the doctor responsible for, Spock berated McCoy for failing to dispense vitamin rations to the crew. (TAS: "Albatross")
When Rear Admiral Gregory Quinn was infected with parasitic beings in 2364, he exhibited extraordinary strength which he attributed to vitamins, stating "They do wonders for the body." (TNG: "Conspiracy")
Sonny Clemonds enjoyed martinis – straight up – with two olives "for the vitamins." (TNG: "The Neutral Zone")
24th century Starfleet rations were, specifically, "concentrated vitamin enriched nutritional supplements" and nourished the body in place of normal food, though their taste often left much to be desired. (VOY: "Innocence"; DS9: "The Siege")
Leola root was a root vegetable native to the Delta Quadrant, and one of the best sources of vitamins and minerals in the quadrant. Neelix introduced the plant to the USS Voyager crew in 2371, and prepared many dishes using it. (VOY: "State of Flux")
The Doctor expressed dismay that the food prepared to celebrate First Contact Day in 2378 had no nutritional value, and suggested that in the future Neelix include a vitamin supplement when he replicated them. (VOY: "Homestead")