It does get absorbed by the body if it's by itself. The key is that, whether it's in your food or a supplement, your body will not take in more than it needs. So unless you're deficient in a particular vitamin, any extra won't get absorbed, and you'll just pee it out. So supplements are good for people with specific vitamin deficiencies, to make up for that lack, but for anyone without a deficiency, they just give you expensive urine.
I speculate a lot of people (in the US) don't eat particularly well.
i.e. the lack of fruit/veg/nuts/legumes/fiber and the amount of fat/sugar/salt/carbs/indirect-crazy-chemicals in food.
My main concern is that when I get "old" I have "X" becz I didn't eat enough "Y". e.g. eat things and potentially take something to help/avoid glaucoma.
At worst (if I'm not stupid) I have expensive urine. With a bit of luck I've reduced my chances of getting cancer/heart-disease/stroke by a few points.
I mean, maybe, but that's definitely a question to ask your doctor. Instead of self-diagnosing with a deficiency that you may not have and then spending money to treat it in a way that does nothing if you were wrong, ask your doctor, get a blood test, and get a real diagnosis to know if you need supplements.
Especially since, as stop50 mentioned in this thread, there are some vitamins that you can actually overdose on without meaning to as they get stored in fat and accumulate. Then you're causing yourself harm based on guessing you might have a deficiency. Doctors, medicine, blood tests: they all exist for a reason. Get the information before taking action, don't make guesses about your health.
This is not correct. An individual nutrient might not be as well absorbable by itself: it might need to be packed with other chemical from REAL foods to be absorbed.
Eg we know that different form of magneisum supplementation are absorbed in a very different % based on which substances they are "packed with".
It becomes even more complicated because certain foods might block nutrient absorption or certain diets might cause a loss of certain nutrients much more (eg high carb vs keto).
While you're right that that some nutrients are better (or worse) absorbed based on what other nutrients you digest at the same time, that doesn't really change the fact that you won't absorb/use more of any given nutrient than you need, so without a deficiency, supplements don't help.
This is only true for vitamins that disolve in water. fat disovable vitamins (vitamin d for example) are stored in the body and can overdose more easily.
True, but I think that means "still not helpful, and possibly even harmful for those"... so still no good reason to take vitamin supplements without a deficiency.
