Optimal Supplement Absorption Guide

Optimal Supplement Absorption Guide

Dec 01, 2010 • By

Vitamin and mineral supplements are meant to provide nutrients that people may not otherwise get, but it's important to ensure that those nutrients can be absorbed and utilized by the body. Such supplement bioavailability varies due to many factors, including when supplements are taken. But literal time of day is less important than is the presence or lack of food in your system, which roughly corresponds to the time of day for most people. Other factors that may inhibit absorption include things like nutrient antagonism – some nutrients cancel out the body's ability to absorb other nutrients – so it's important to be aware of these interactions.

Generally speaking, it's best to take vitamins and minerals with food to ensure optimal supplement absorption, especially if they're likely to upset your stomach. For example, multivitamins and minerals should be taken with food. Eating some protein with mineral supplements will aid in the body's ability to absorb and utilize those minerals. That said, there are some kinds of supplements that require an empty stomach to be absorbed properly.

Fat-soluble Supplements

Fat-soluble supplements like vitamins A, D, E, K, coenzyme Q10, and fish and flax oil require fat to be absorbed properly. These supplements should be taken with food that has some fat content. Fat-soluble supplements get stored in the liver and other fatty tissues, so they may stay in your system for longer periods of time. The exception is vitamin K, which isn't absorbed or stored well, but can be synthesized by your good intestinal bacteria, which is part of why vitamin K deficiencies are less common.

For those taking a vitamin E supplement, you may want to choose one that's derived from natural sources, rather than the synthetic kind. The body absorbs natural vitamin E slightly better than synthetic (Rock). Natural vitamin E will be denoted as "d-alpha" on its label, as opposed to the synthetic forms denoted by "dl-alpha."

Water-soluble Vitamins

Vitamin C and the B vitamins are water soluble, meaning they dissolve in water. These supplements do not get stored in the body, so they need to be taken every day. Vitamin C passes through your system in around 3 hours. To keep levels up, you should separate doses of vitamin C and take them throughout the day. Interestingly, vitamin C may aid in the absorption of iron. Researchers have found that "vitamin C interacting with inorganic iron may enhance bioavailability of the iron" (Yetley). So if taking iron supplements, pairing them with vitamin C supplements may be helpful. Vitamins B and C are also anecdotally reported to be best in the mornings, providing an increase in energy levels. This effect hasn't been scientifically proven and the supplements are still effective at other times of day, however.

Amino Acids

The naturally-occurring amino acids in food compete with amino acid supplements, causing lower absorption for both. Because of this, amino acids need to be taken on an empty stomach. It's easiest to do so in the mornings, when you know you haven't had anything to eat for several hours. Otherwise, you can take amino acids 1 hour before eating or 3 hours after your last meal. Eating more necessitates a longer time period for your stomach to empty, so adjust accordingly.

Calcium and Magnesium

Calcium is best absorbed with other nutrients, so it's ideal to take with meals. Calcium should be taken in doses of a maximum of 500mg, ideally at breakfast and dinner (Rock). But be careful not to take calcium at the same time as iron or a multivitamin containing iron. These two minerals are antagonists, resulting in less absorption of both. Researchers have found that "decreasing the levels of magnesium and calcium increases the bioavailability of iron" (Yetley). Calcium often comes paired with magnesium - the two work well together and may aid in sleep, so they're both best at night.


Like calcium and magnesium, zinc absorption is also inhibited by iron supplements. "Iron can have a negative effect on zinc absorption, if given together in a supplement, whereas no effect is observed when the same amounts are present in a meal as fortificants" (Lönnerdal). Research has found that protein from meats aid in absorption of zinc, but protein from milk can inhibit it. "The amount of protein in a meal has a positive effect on zinc absorption, but individual proteins may act differently; e.g., casein has a modest inhibitory effect of zinc absorption compared with other protein sources" (Lönnerdal). For optimal supplement absorbtion, zinc should be taken apart from iron supplements, but with some animal protein.


Do not mix fiber supplements with any other kind of supplement. Research has found that the "addition of cereal fiber to human and animal diets has been found consistently to depress absorption and retention of calcium, magnesium and zinc, and usually to depress absorption of iron" (Greger). Fiber binds minerals, making them unavailable for the body to absorb or use. Thus, if taking a fiber supplement, it's best to take it apart from all other supplements.

Supplement Antagonists

Some supplements do not play well with others. Calcium absorption may be inhibited by iron, zinc, or vitamin A. Magnesium absorption may be inhibited by potassium, selenium, or iron. Absorption of the A vitamins may be inhibited by vitamin D, zinc, or vitamin E. Vitamin D absorption may be inhibited by vitamin K, calcium, or vitamin A. These inhibitory effects may only occur at higher doses, however, so it's best to be mindful of how much you're taking and at what levels the nutrients interfere with one another.

Supplement Form

If you have a choice in the form of supplements, gelatin capsules may be easier for the body to break up and absorb. Researchers have found that "[soft elastic gelatin] capsules because they represent liquid fills, as opposed to hard gelatin capsules, which encapsulate a dry-powder blend, often tend to be better absorbed" (Thakker et al). Similarly, supplements in liquid form may also be easier for the body to absorb.

General Guidelines

Always make sure to read the instructions on the label. If a supplement label says to take it with food, it means solid food, not protein shakes or the like. Some supplements need to be mixed with solid food in your system, slowing their passage through the body and allowing you to absorb more. If a supplement should be taken with food, it's better to take in the midst of a meal or immediately after.

Always drink plenty of water when taking supplements. Never lie down immediately after taking them. If you're taking a large amount of a certain nutrient, try and spread doses throughout the day so as to avoid stomach irritation. The body can only absorb a certain amount of a nutrient at any given time. The rest passes out of your system. Thus, it's always better to break up large doses of supplements, ensuring you get the optimal supplement absorbtion throughout the day.

While it's best to take your supplements every day, if you miss a day every once in a while, it's not a problem (Rock). Similarly, if you've been taking supplements at a sub-optimal time, don't become too concerned. The absorption likely only drops around 10%. Of course, the ideal is to maximize your absorption of any supplements you take, so while it's not a crisis if you haven't been taking them at the optimal times, you should make every effort to do so in the future.

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Greger JL. "Nondigestible carbohydrates and mineral bioavailability." The Journal of Nutrition. 1999. 129: 1434S-5S.

Lönnerdal B. "Dietary factors influencing zinc absorption." The Journal of Nutrition. 2000. 130: 1378S-83S.

Rock A. "Vitamin Hype." Money Magazine. September 1995. http://money.cnn.com/magazines/moneymag/moneymag_archive/1995/09/01/205710/index.htm

Thakker KM, Sitren HS, Gregory JF 3rd, Schmidt GL, Baumgartner TG. "Dosage form and formulation effects on the bioavailability of vitamin E, riboflavin, and vitamin B-6 from multivitamin preparations." The American Journal of Clinical Nutrition. 1987. 45: 1472-9.

Yetley EA. "Multivitamin and multimineral dietary supplements: definitions, characterization, bioavailability, and drug interactions." The American Journal of Clinical Nutrition. 2007. 85: 269S-276S.

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