What Can Affect the Absorption of Multivitamins?

Many of us take a multivitamin every day to make sure we aren’t missing any of the vitamins and minerals we need.  But did you know that you may be losing some of the benefits from multivitamin?  Sometimes other factors can affect how much of the nutrients your body absorbs.

What Is Bioavailability?

The official term for this is bioavailability.  This refers to how much of a nutrient that someone consumes in their diet is then absorbed and used by the body. Lots of things can affect bioavailability. For instance a person’s diet, how concentrated the nutrient is, how healthy the person is, and the person’s age can have an influence. What you eat can also affect how much of your multivitamin you absorb. Eating certain foods together can also influence how the body absorbs various micronutrients because some components of foods interact with other foods, leading to less absorption than expected.


multivitaminsOne you may have heard about is iron.  Iron from plants in particular is hard to absorb.  However studies show that vitamin C can capture iron and store it in a form that’s more easily used by the body. Vitamin C can be found naturally in foods such as vegetables and fruits, especially citrus.  On the other hand, things like calcium, eggs, tannin, and oxalates inhibit the absorption of iron.  Oxalates are found in foods such as spinach, kale, beets, nuts, chocolate, tea, wheat bran, rhubarb, strawberries and herbs such as oregano, basil, and parsley. Ironically, because of the oxalate in spinach your body hardly absorbs any of the iron in it. Any iron Popeye got from spinach would probably have been from the minute particles of sand or dirt clinging to the plant, rather than the iron contained in the plant.  So always check your multivitamin to see that is has both vitamin C and iron.

Calcium and Vitamin B12

Calcium and vitamin B12 are two micronutrients that affect each other. Even though you may eat plenty of foods that contain calcium, your body has to have other nutrients, especially vitamin B12, to help you absorb this mineral to obtain its full benefits. On the other hand, to absorb vitamin B12, pancreatic enzymes have to bind it to a protein known as intrinsic factor. The small intestine can only take up vitamin B12 and intrinsic factor complex when calcium is present. Any multivitamin must have both calcium and vitamin B12 together for it to be effective.


Some antioxidants can bind with certain micronutrients in the gastrointestinal tract and prevent absorption into the body. One such antioxidant is phytates.  Foods, such as grains, nuts and legumes are high in phytates can bind with minerals like zinc, calcium or iron, which prevents their absorption in the intestines. To counteract this you can soak, sprout or ferment high phytate foods. It might also be a good idea to bear this in mind when you are taking your multivitamin.

When Should You Take Your Multivitamin?

You also need to consider when you take your multivitamin. It’s a good idea to get into a routine of taking your vitamins at the same time every day.  Some multivitamins are designed to be taken on an empty stomach whereas others are designed to be taken with food.  With many multivitamins the best time to take it is just before lunch on an empty stomach.  Remember to drink orange juice not milk if you are taking iron.

Vitamins can be divided into two types – fat soluble and water soluble. It won’t be a surprise to learn that this describes how they dissolve. Vitamins that come into this category include vitamin A, vitamin K, vitamin E, and vitamin D.  These vitamins are therefore best taken in the evening with a meal that contains saturated fats or oils to help you absorb them. Excess amounts of these vitamins can build up in the body and become toxic.  Water soluble vitamins on the other hand are best taken first thing in the morning, half an hour before eating.  Failing that, it is advisable to wait two hours after a meal. Because these vitamins dissolve in water your body can use them easily and any excess is excreted.  Vitamins that fall into this category include vitamin C, all B vitamins, and folate (folic acid).

Some prescription drugs can also affect how your multivitamins are absorbed.  It’s always advisable to check the instructions on your medicine to make sure there are no conflicts.

As you can see, there is a lot more to consider with multivitamins than just which one to take!