Multivitamin supplement: A factor in the maintenance of good health and to help the body metabolize proteins. Stress, aging, active lifestyles, poor digestion, alcohol consumption, PMS, menopause, and cardiovascular disease are just some of the factors that increase the body’s need for B vitamins and why so many people can benefit from supplements. Inadequate intake of some B vitamins is not uncommon and deficiencies can be associated with fatigue, insomnia, depression, and migraines. In the diet, B vitamins are found in yeast, green leafy vegetables, and lentils. The best sources of B12 are meat and seafood, making supplements particularly advisable for vegetarians.