Interesting article about supplements in this week's New Scientist - newscientist.com/article/mg... (Subscription required)
Their final conclusion is that most people don't need to take any supplements unless recommended by a doc. This was a very interesting paragraph...
As we age, we begin to produce less stomach acid, which can impede our ability to absorb certain nutrients from our diet. One of these is vitamin B12, used to make red blood cells, nerves and DNA. Adults over the age of 50 are therefore often deficient in this nutrient, and should either consider getting more of it from supplements or fortified foods, including some breakfast cereals.