Key takeaways

Bioavailability, the measure of how much of a substance is absorbed by the body, is crucial for the effectiveness of dietary supplements, with factors such as form, type, concurrent food and drink intake, and other medications affecting absorption.
Specific strategies to enhance the absorption of supplements include taking calcium with vitamin D, iron on an empty stomach with vitamin C, magnesium with carbohydrates, and turmeric with black pepper, alongside considerations for the timing and combination of other supplements.
Certain supplements can interact negatively with medications and medical conditions, emphasizing the importance of consulting with a healthcare provider before beginning any new supplement regimen.
Despite the widespread use of dietary supplements, they may not be necessary for everyone and should ideally be considered as short-term solutions, with a balanced diet and healthy lifestyle being paramount for nutrient absorption and overall wellness.

Did you know that more than half of all Americans aged 20 and older take dietary supplements? In fact, 80% of women aged 60 and older take some kind of supplement. The bioavailability of vitamins is one thing that many people fail to consider when they add vitamins or supplements to their diet. Bioavailability is how readily your body is able to absorb the nutrient, which plays a large role in how effective a supplement or vitamin is. If you’re not sure that you’re getting the most out of your supplements, keep reading.

What is bioavailability?

Bioavailability is the scientific term for how much of a nutrient is absorbed or made available to the body. In other words, just because a food or supplement contains a specific nutrient, it’s not a guarantee that your body is actually able to absorb and put it all to use. Some nutrients are more bioavailable than others. If your body can’t absorb the substance, it won’t reap any of the benefits.

How are vitamins absorbed by the body?

When you ingest something, it moves through your digestive system. Your body absorbs helpful nutrients for use by your cells or stores the excess. But not everything is able to be used. Those nutrients that aren’t bioavailable are destroyed or excreted. That means just because a food has a particular micronutrient or vitamin in it doesn’t necessarily mean that your body is putting it to use. Absorption matters, and quite a few things can affect vitamin absorption.

What affects vitamin absorption?

Because all vitamins and minerals are different, what affects each’s bioavailability varies. A major thing for people to consider is the correct type of the vitamin or micronutrient, says Tanja Barco, APRN-CNP, a certified functional medicine nurse practitioner with MetroHealth in Cleveland, Ohio. Things that can affect vitamin absorption include:

Form (e.g., tablet vs. liquid vs. powder)
Type (e.g., calcium carbonate vs. calcium citrate)
What you eat when you take it
What you drink when you take it
Other medications, such as acid reflux medication or metformin
Gastrointestinal issues, such as celiac disease, pancreatitis, or Crohn’s disease

How to absorb vitamins better

The best way to absorb vitamins when you’re taking supplements is to know the best practices to maximize absorption for each type—and to work with your healthcare provider to determine the best form for your condition. Here is how to maximize bioavailability of supplements.

1. Take calcium with vitamin D

Taken to help prevent osteoporosis, the two most common forms of calcium are carbonate and citrate. Calcium carbonate is usually less expensive, but calcium citrate has fewer side effects—and both are better absorbed by the body when taken with food. Vitamin D helps calcium absorption.

Choose a calcium supplement that’s combined with vitamin D, or take calcium alongside vitamin D-rich foods, like eggs (with the yolk), mushrooms, and fatty fish. Calcium supplements are available as capsules, tablets, powders, and chews—and they are better absorbed in smaller doses, so stick with doses of 500 mg or less (taken several times daily).

Calcium supplements can interfere with some common medications, including certain antibiotics, thyroid medication, and more, so be sure to disclose to your healthcare provider or pharmacist if you’re taking this supplement.

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2. Take iron an hour before a meal

Iron helps transport oxygen in the blood and is found mainly in animal products or iron-fortified foods, like grains. Iron supplements help replace iron more quickly than just adding more iron-rich foods into your diet, so your provider might recommend supplementation if you’re low on iron or have been diagnosed with iron deficiency anemia.

Iron bioavailability is affected by how much iron is already in your body. Low iron means greater bioavailability, while having higher levels of iron already means your body will absorb less from supplements. To improve absorption even more, take your iron supplement on an empty stomach, either one hour before or two hours after a meal. A source of vitamin C, like orange juice, might help you absorb slightly more iron.

Iron is available in various forms, including tablets and liquid. If you’re taking a capsule or an extended-release tablet, be sure to take them whole, not crushed or chewed. Also, avoid taking iron with tea, coffee, milk, or soda, as these reduce absorption of iron. It’s also believed that iron absorption can be affected by calcium, so if you are taking both supplements, it’s best to take them at different times of the day.

Certain antibiotics, thyroid disease medications, Parkinson’s disease medications, and antacids can be affected by iron supplements; let your healthcare provider know if you’re taking these.

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3. Combine magnesium with carbs

Magnesium is necessary for your body’s muscles and nerves to work properly. Common types of magnesium include oxide, citrate, l-threonate, glycinate, chloride, and aspartate. The type of magnesium you opt for will depend on what you’re using it for—for example, magnesium citrate works best for muscle cramps; and l-threonate may improve sleep, anxiety, and migraines. The type most providers prescribe is magnesium oxide. Magnesium is available in a variety of forms, including tablets, powders, and transdermal—or skin-based varieties—like oils and lotions.

Combining magnesium supplements with vitamin D, whether through supplements, sunshine, or vitamin D-rich foods, including cheese, eggs, or fortified grains, may help magnesium bioavailability. Combining magnesium with carbohydrates like grains might help as well.

If you’re taking zinc supplements as well, it’s best to not take them together with magnesium. Magnesium can interact with certain antibiotics, osteoporosis medications, and some thyroid and heart medications. Additionally, if you have kidney disease, you should check with your doctor before taking magnesium supplements.

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4. Eat black pepper with turmeric

Curcumin is the main ingredient in turmeric, a spice that has been used for thousands of years in Asian and Indian cultures for its healing properties. Turmeric supplements have grown in popularity, but their effectiveness is difficult to measure because curcumin is unstable—it changes into another substance easily—and it’s not well absorbed by the body when taken orally.

Piperine, one of the compounds in black pepper, can improve absorption of curcumin and turmeric bioavailability. You can either take a piperine supplement along with curcumin, or enjoy your turmeric-infused foods with a hearty dose of freshly cracked black pepper. Curcumin supplements or turmeric spice should also be combined meals that include fat, like avocado or olives, says Jacob Hascalovici, MD, Ph.D., the co-founder and chief medical officer at Clearing chronic pain care. (This is also true for fat-soluble vitamins, like vitamins A, D, E, and K.)

Turmeric may interact with certain medicines, such as blood thinners and antacids, so check with your provider before taking turmeric.

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5. Ingest vitamin B12 in the morning

This vitamin is important in creating red blood cells and is found naturally in animal foods. If you supplement B12, your body will only absorb as much as it’s missing, and anything excess will be excreted when you urinate. Most vitamin B12 supplements are made up of cyanocobalamin, a synthetic form of the vitamin. It’s readily absorbed by the body and more inexpensive to manufacture.

B12 is a water-soluble vitamin, so taking it with water on an empty stomach will help B12 absorption. One positive side effect of vitamin B12 supplements for some people is a boost of energy, so taking it in the morning is best.

Taking B12 with vitamin C can reduce B12 bioavailability, so if you’re taking both supplements, it’s best to keep them a few hours apart.

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6. Take zinc with protein

A mineral crucial for much of the body’s functions, like the immune system and blood clotting, zinc is a common supplement. As a supplement, you can buy zinc as pills, lozenges, or as a dissolvable powder. Zinc sulfate is usually the cheapest, but it’s the form least easily absorbed by your body and can lead to stomachaches. Good alternatives include zinc citrate or zinc glycinate.

Food can affect zinc bioavailability. Zinc is best taken with water or juice on an empty stomach, either one hour before or two hours after a meal, although if it upsets your stomach, it’s okay to take it with food. Protein may improve zinc absorption, but casein, a protein found in dairy products, may slightly inhibit absorption.

High levels of zinc can inhibit copper absorption, so if you are taking a zinc supplement, you should consult with your provider about adding copper supplementation as well (or taking a zinc supplement that contains copper). Iron and calcium supplements should not be taken at the same time as zinc, as they can inhibit absorption. Zinc can also interact with certain antibiotics, blood pressure medications, nonsteroidal anti-inflammatory drugs (NSAIDs), and diuretics.

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7. Take vitamin C on an empty stomach

Vitamin C is crucial for keeping cells healthy, maintaining and repairing body tissue, including skin and bones, and helping wounds heal. Most vitamin C supplements are composed of synthetic ascorbic acid, which has similar bioavailability to naturally occurring ascorbic acid found in foods like fresh oranges and cooked broccoli. Vitamin C also comes in a couple other forms: mineral ascorbate and time-released capsules.

Vitamin C can’t be stored in the body, so if you take in any more than you need, you will urinate the excess. As a water-soluble vitamin, it’s recommended you take vitamin C with water and without food. But if you are sensitive to acids, taking it at mealtimes can help with any stomach side effects—or you can try a buffered vitamin C, which is gentler on the stomach. Both natural and synthetic vitamin C seem to be equally bioavailable. Bioflavonoids can help you absorb vitamin C.

Vitamin C can interact with radiation or chemotherapy, so if you have cancer, consult your doctor before taking any vitamins or supplements. It can also interfere with estrogen levels if you are on hormonal contraception or hormone replacement therapy. Some other medications such as warfarin (blood thinner), statins (for cholesterol), and certain antiviral drugs can be affected. Those with kidney disease should also speak with a healthcare provider before taking vitamin C.

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The bottom line: Are supplements worth it?

Before taking vitamins or supplements for deficiencies, you should consult your healthcare provider to see if it’s necessary. Your physician can test you for most deficiencies or make sure that any symptoms you might have are actually from a deficiency and not something else.

Some groups of people really benefit from vitamin supplementation, like those who are pregnant, have restrictive diets (whether by choice or by medical necessity), or have limited exposure to sunshine. For most people, supplements aren’t necessary and, if they are, should be considered a short-term solution for a bigger problem, says Dr. Hascalovici.

It’s also important to disclose what you’re taking in case any prescriptions are made less effective by your supplements. “As with many health habits, when it comes to vitamin and mineral absorption, it’s good to be aware of the overall science, to practice balanced eating and exercise habits, as exercise can help boost levels of certain vitamins, like vitamin D, and to know your specific health-related goals so you can develop specific absorption strategies,” Dr. Hascalovici says.

When taking vitamins, there are general rules that apply:

Stick to the recommended dosage unless otherwise instructed by your provider.
Avoid alcohol at the time you take your vitamins.
Take fat-soluble vitamins at a meal that includes some kind of dietary fat, like avocado or olive oil.
Take water-soluble vitamins on an empty stomach.
Keep a few hours between vitamins and that cup of coffee. Caffeine can affect supplement absorption.
Avoid smoking at the same time as taking your vitamins. In fact, quitting smoking will likely do more for your health than any supplement could.

Finally, keep in mind that the Food & Drug Administration regulates supplements as food, not drugs. Meaning, they are not evaluated for safety and efficacy. Be wary of taking any supplements that sound too good to be true and get them vetted by a healthcare provider first.