Are Absorption and Bioavailability the Same?

Are Absorption and Bioavailability the Same?

Posted by EyePromise on Mar 3rd 2022

When we take a medicine or supplement, we expect our bodies to be able to use it with no problem. Unfortunately, this isn’t always the case. It all depends on the ingredients, delivery method, quality, and, ultimately, your body. Learning what your body needs for optimal absorption and bioavailability is the first step to understanding what supplements you need. Actually, the first step is knowing the difference between absorption and bioavailability.

According to Paul Abialbon of the Department of Pharmacology & Clinical Skills, Medical University of Americas, Charlestown, Nevis, “absorption is the movement of a [substance (drug, vitamin, mineral, etc.)] from the site of administration to the systemic circulation. Bioavailability is the extent to which absorption occurs.” We’ll get into a bit more details to help you better understand the difference and what they mean for you.


The definition of absorption is “the process or action by which one thing absorbs or is absorbed by another.” For health purposes, it’s classified as the absorbing or digesting of substances into cells or across tissues and organs. This is typically done through the processes of diffusion or osmosis. Absorption can occur throughout the body, including the skin, mouth, stomach, and intestines. While absorption happens naturally with food, we typically think of it in reference to medicines or supplementation.

An important note when thinking about absorption: it completely depends on your body. Everyone is different, and that includes your body’s natural ability to absorb nutrients. Some people don’t absorb vitamins and minerals like they should. Often, this or lack of ingestion is what sparks a supplementation recommendation.


The definition of bioavailability is “the proportion of a [substance (drug or other)] which enters the circulation when introduced into the body and is able to have an active effect.” It’s the amount of a substance your body can distribute and use in the intended destination. Bioavailability is important because nutrients can do nothing for you if your body can’t get them where they need to be.

Type of Nutrient

Bioavailability can depend on the type of nutrient that is attempting to be used. Macronutrients (carbs, fats, and proteins) have a much higher bioavailability than most micronutrients (vitamins, minerals, flavonoids, carotenoids, etc.). Another reason these types of nutrients are common in dietary supplements.

Delivery Method

Delivery method can also play a huge role in bioavailability. For example, administering a substance via injection (i.e., directly into the bloodstream) helps ensure it will have the full intended impact. This is because it doesn’t go through any of the body’s natural filtration system like the liver and kidneys and it doesn’t get partially degraded by stomach acid. On the flip side, when you take something through a pill/tablet/powder form, you run into the possibility that the necessary nutrients you need may not make it to their intended destination.

How Absorption and Bioavailability Affect Supplementation

Bioavailability is the key to creating a supplement that delivers proven benefits. Bioavailability and absorption are part of the reason supplementation can take time to have an impact. While absorption is mostly unchangeable, the bioavailability of supplements can be affected and, in some cases, enhanced. Factors that can affect bioavailability in supplements include:

  • Formulation – the body absorbs some nutrient forms better than others, like those from dietary sources.
  • The delivery method – though some “quick release” forms are better for things like headache relief, there’s no scientific consensus that absorption/bioavailability is better with different delivery methods.
  • Taking it with food – the body absorbs certain nutrients (i.e., fat-soluble nutrients) better when taken with a meal that has some fat content. Think butter or avocado toast.
  • Potential interactions – some nutrients can interact with other substances in your system, like calcium supplements making it more difficult to absorb iron. Talk to your doctor about any potential issues.
  • Your health – as mentioned, everyone is different, and so is our bodies’ ability to absorb nutrients. Different health issues can add to this complexity, like poor gastrointestinal health or inflammation.

Beyond these, improving the bioavailability of supplements relies heavily on the ingredients and varies for each nutrient. For example, the active ingredient in turmeric, called curcumin, is fat-soluble and should be ingested with an oil or fat for best absorption.

Understanding absorption and bioavailability fully is a more complicated task, but this general knowledge can help guide you to selecting the right supplements for your health needs. When it comes to vision supplements, getting the nutrients to your eyes is critical. EyePromise® develops clinically proven eye vitamins created with the highest quality, natural ingredients for best use in your eyes. Find out which EyePromise eye vitamin is right for your eye health needs!