To back up a bit – let me say that I am a strong believer in good nutrition. From a basic science point of view, it just makes sense. We need specific nutrients for various biochemical reactions in our bodies. Deficiencies are clearly related to specific diseases. Further, in areas where nutrition is poor overall development is also poor. The connection is clear.
The question of routine supplementation, however, goes further. It asks whether or not taking vitamin supplements are necessary or helpful for someone who has a reasonable diet and does not have any specific disease or condition that would impact their demand for specific vitamins – i.e. routine. In most wealthy industrialized nations lack of quality food is not a problem for most people. Also, modern methods of growing, preserving, and shipping food means that more people have access to a wider variety of foods all year round.