There are many reasons people overdose on vitamins, and in some cases they are not even aware of this condition until it shows up in some medical test, which is brought on by an illness. Overdosing could be due to a number of reasons and most are simply due to the individual being careless or ill informed.
Taking vitamin supplements without proper medical supervision is also not advised, as some vitamins may react adveresly to other medications the individual may be taking for a medical condition.
Taking vitamin supplements may cause other medications to mutate or at the very least become non effective in treating the ailment it was prescribed to treat.
This of course could result in a very dangerous situation for the individual. There are also some vitamins known to counteract other vitamins when taken together. Following the dosage prescribed on the container is very important as any deviation could result in an overdose, especially when taking extra just to make up for the skipped sessions.
Another way to ensure the individual is not likely to overdose on the vitamins taken, is to have periodic blood tests done, as negative elements will show up clearly in the reports drawn up from the rests.