A B-complex is referred to all of the known essential B-vitamins which include: B-1 (thiamine), B-2 (riboflavin), B-3 (niacin), B-5 (pantothenic acid), B-6 (pyridoxine), biotin, folic acid and B-12 (cobalamin). There are other members of the B-vitamins, most notably choline, inositol and para-aminobenzoic acid (PABA), but considered non-essential. Each B-vitamin has a different role in the body, but when together, they convert protein, fats, and carbohydrates into energy, and can also help with mood and nerves.
The general requirement for each B-vitamin varies considerably and depends on each person taking them. So, taking equal amounts of each vitamin B, as found in many B-complex supplements, makes little sense. Furthermore, taking larger doses of B-complex, like a B-100 complex, do not appear to offer any more benefits unless a person is deficient in one or more of them.
Most multivitamin-mineral products contain B-complex along with other vitamins and minerals. Since they are more complete than B-complex vitamins alone, multiple vitamin-mineral supplements are found to be more popular to improve overall micronutrient intake and prevent deficiencies.