Take them with or without food?
A very simple mistake can be made when taking a supplement without food. Some vitamins like vitamin C or B9 are quite acidic and can make you feel sick if you eat them on an empty stomach. If your supplement contains a lot of those vitamins, make sure to always have it with food. On the other hand, some vitamins, especially fat-soluble A, D, E, and K absorb better without food. And iron is best absorbed on an empty stomach, but also causes nausea when taken without food. So it’s best to read the label or ask the manufacturer how the supplement should be taken.
You can overdose on some vitamins
Vitamins B and C are water-soluble, which means they aren’t stored in your body. If you have an excess, you will just pee them out. But fat-soluble vitamins do stick around and can be toxic in high concentrations. If you notice having trouble sleeping or concentrating or if you feel more irritable after introducing a new supplement, then that’s a warning sign that something’s wrong.
When you’re choosing a multivitamin, take your time and check what percentage of the recommended daily value of vitamin A (or beta-carotene as its precursor), E, D, and calcium it contains. These nutrients are relatively easy to get from food (and sun exposure) so you can easily create an excess with a poorly chosen supplement.
You’re not absorbing anything
Not all pills are created equal. It depends on the manufacturer what type of binding, filling, and flow agents they use in their pills and what kind of coating they use on the outside. Even though these substances make production easier and allow for a longer shelf life, they can make the pill slower to dissolve in the stomach and the minerals and vitamins harder or impossible to absorb.
Make sure to read through ingredients carefully before you put your trust into a supplement, be very picky and go for quality! Otherwise you might as well be flushing money down the toilet.