What determines the expiration date of vitamins?

I've been told that the expiration dates on the bottles of vitamins are of no real value as they are still good for several months after that. If this is true then why bother to put one on them?

If the vitamins are oil (fat) soluable like Vitamin E, the oil can go rancid. If the vitamins are water soluable...theoretically water can get into the pills and break down the vitamins, but if you never open the bottle, what are the chances?

Why worry about it. If you buy a 60 day supply and get an expiration date of, say, 2 years - you and me don't have to worry about it.

Vitamins & expiration dates?

I have been taking fruit & vegetable supplements for a long time ago but I never realized their expiration date until my dad marked the expiration dates on the box. Anyway, my box of vitamins expired in 09/2008 & I took them up until Sept. 30th

In my opinion they will still be good for probably about three months past the expiration date. After that toss them out. That's speaking of vitamin supplements only. Prescription drugs should be discarded as soon as they reach the expiration date.

Is the expiration date on vitamins the start of the decline or the end of total decline in efficiency?

Usually the start, however it varies from to product how long they will be effective after the expiration date. For example I wouldnt use a probiotic too long after expiration date, however I still use other supplements after their date and they are fine.

How long after the expiration date on vitamins should you stop using them.?

You should stop using them the day after the expiration date.