There are many health risks when taking high potent vitamins (unless there is an extremely high deficiency in which case they would be prescribed by a physician); just one example is that an overdos e in Vitamin C can cause a threat of free radical production within the body.
High intake of Vitamin E can lead to excessive thinning of the blood, and in extreme cases, increasing the possibility of even death.
Although this is not advised to frighten you, you must be aware of the risks. Taking a good range and healthy amount of vitamins and minerals, when taking a good quality product, is extremely good and beneficial to your health.
There are items that have been studied for years which can be much more powerful than some vitamins which have quite a weak antioxidant property. All of which do fight off and scavenge free radicals and prevent damage to cell damage. However, these items are so much more powerful and you do not have to take these in huge amounts either.
An example of a natural powerful antioxidant is alpha lipoic acid, which is much stronger than high potency vitamins such as C or E as listed above, these also come minus the health risks, as you do not need to take as much to reap the same health benefits.
As minerals work together, it is important that scientists with approved and trusted credentials formulate the product. There are a lot of products, which are just quickly put together, in many cases, ingredients end up overriding each other, therefore, not getting the benefit for which you bought the product. Many showing not to have any effect at all.
Choosing a manufacturer that follows pharmaceutical GMP compliance is a good idea as many supplements created in the US are not regulated and therefore have no effect.