Several years ago a major drug company claimed that its vitamin pills helped to relieve stress from the "complications of everyday life" and gave their products names such as "StressTabs." The New York Attorney General forced them to stop their deceptive advertising, but many people still remember and believe this claim.
There is no evidence that stress increases your needs for vitamins or that taking vitamins will help you handle stress. When you eat vitamins in pills or in your food, they go into your bloodstream and then into cells. They function by combining with other chemicals in cells called apoenzymes, to form complete enzymes that cause reactions to proceed in your body. All chemical reactions in your body require enzymes to make them go, and that is why vitamins are essential. For example, all of the B vitamins form enzymes that convert food to energy. But since enzymes only start chemical reactions and are not used up by them, they can be used over and over again and only minuscule amounts are needed from your diet.
In the 1930's, Hans Selye of McGill University in Montreal reported that the adrenal glands contain the highest concentration in the body of vitamin C. The adrenal glands make cortisol from vitamin C. When a person is under stress, the adrenal glands make tremendous amounts of cortisol and the concentration of vitamin C in them drops. However, scientists have known for more than forty years that the levels of vitamin C in the adrenal glands are still high enough to continue to produce cortisol and that giving extra vitamin C will not increase production of cortisol. So the myth that vitamins treat stress is based on a misinterpretation of one study on one vitamin, and that research did not show that taking extra vitamins prevents or treats stress.