Whether there is a need for taking daily vitamin supplements is probably one of the questions I get asked most during consults. The answer is: Yes, No, Maybe!
For those who eat really well--meaning, home prepared natural foods, with a good balance between carbs/fats and protein, vitamins may seem unecessary. For those who have been ill, are experiencing some minor health concerns and who are not eating well, supplements are a definite- Yes. For those who are doing well and want to do better by taking mega-vitamins or more than the RDA, the answer is - No.
To complicate matters even more, studies are streaming out in the last few years regarding the diminishing amounts of nutrients found in fresh fruits/vegetables, largely due to environmental, farming and storage practices. An article in Mother Earth News http://www.motherearthnews.com/ , details how essential nutrients, such as protein, calcium, iron, B vitamins, C and phosphorus in todays foods are way below levels found 50-100 years ago. They cite "Environmental Dilution"-which occurs when too much fertilizer is used, causing plants to take up excess water. The result is a sometimes larger yield, but less nutrient dense. Another problem is "Genetic Dilution" caused by hybridization and GMO activity that improves appearance, shipping viability or survival in unintended climates, thereby changing the nature of a particular food.
This, of course, causes a domino effect in our diet since animal feed comes from plants, we are finding less nutrients in milk, meat, eggs and all dairy products.
My advice is to supplement a healthy diet a few times a week with ORGANIC vitamins/minerals, to take a daily organic multi- vitamin/mineral supplement if you are suffering from or recovering from illness or have exessive amounts of stress.... and to never take mega- vitamins. More is usually never, better and instead can throw off the vitamin/mineral balance in our bodies and are very difficult to digest and metabolize.
Moderation always wins the day, but we now have to reverse and compensate for practices we have little control over in the short run. So, to start, do take seriously getting most of your food fom local organic growers, if you plant gardens, rely heavily on heirloom varieties... and become political about food and farming. Our lives do depend upon it.