Bioavailability is the degree and rate at which a substance is absorbed into a living system or is made available at the site of physiological activity(Mirriam Webster definition).
Basically that means…how much of it can your body actually use?
The problem is that bioavailability will vary for every person. Not only that but each type of medicine you take will be different too.
There are some medicines and vitamins that claim a certain percentage will be absorbed…but that is highly unlikely to be accurate because every person that takes it will react differently.
Some folks (like me) can’t take full dosages of some medications because their bodies react more than usual. A full dose of some cold medications will make me feel dopey(and probably act that way too).
Not only is each persons body different but some people have a tendency not to follow directions. And that can make a huge difference too.
Some medications need fats to be taken with them so they get absorbed…some need other things. That is one reason why many pills require you to take them before or during meals.
Some need to be taken at a certain time such as before bedtime…so they are more likely to actually get absorbed and do some good.
Now some vitamins are made with other things (chelated) to improve the absorption but even so they can’t really say for sure that every singly person will get a definite amount.
There are some vitamins and supplements that have been extensively tested so it is known how much benefit most people will get out of them.
You have to read the information carefully though…sometimes it isn’t easy to tell if it a supplement has been tested or if the company is just trying to sell more.
So you have to be very careful when reading the labels and other information..