Bioavailability: What Does It Refer To?

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In the United States, billions of dollars are spent every year by consumers in an effort to maintain health and wellness. Money is spent on nutrient-dense foods, wellness supplements, and more. 

Unfortunately, many people simply believe that eating nutrient-rich fruits and vegetables or taking multivitamins is where the road to wellness starts and stops. But this is only half the battle. 

Many don’t realize that the numerous health benefits associated with the top vitamins and minerals only take effect if our bodies can absorb them. This principle is known as bioavailability. 

Understanding Bioavailability

In short, bioavailability refers to how efficiently and effectively your body absorbs and uses a given nutrient. This applies to macronutrients and micronutrients, like vitamins and minerals. 

Now, that may sound cut and dry, but the process can be quite complicated. We assume that once we’ve consumed the nutrient, either by food or supplement, the efficacy of the health benefits is a given — but that just isn’t true. 

The problem is, there is a lot of competition when it comes to nutrient absorption. Not only do nutrients compete for absorption, but some actually block absorption for others. So, when it comes to nutrients (and especially supplements), timing is key. 

Intravenous administration of a developmental drug can help provide valuable insight and information on the fundamental volume(V) of distribution and clearance(CL).

In terms of pharmacology, relative bioavailability measures the bioavailability of a formulation of a certain drug compared with another formula of the same drug. 

Clearance is measured by the drug elimination rate divided by the plasma drug concentration. 

How Does the Body Absorb Nutrients?

Our body survives and thrives off of the various nutrients we consume through our food and supplements. In fact, without nutrients, food would be completely useless. 

Essential nutrients are needed for every single function in the body, from immune support to brain health. But how does the body actually absorb all the rich benefits of these nutrients?

In short, nutrients are absorbed through the process of digestion. There are two marked stages of digestion, beginning in the mouth and continuing through the gastrointestinal tract. 

The first is referred to as mechanical digestion, where food is chewed, mashed, and broken down in the mouth. But chemical digestion is also happening. Digestive enzymes in the mouth and stomach help break down the chemical structure of food.  

How the Process Works

  • Chewing allows for the introduction of digestive enzymes into the mouth (salivary amylase); this helps break down the food's chemical structure.
  • Next, the mixing and churning with stomach acid helps break down the food even further.
  • The real process of nutrient absorption begins in the small intestine, particularly through the brush-like lining known as villi.
  • Once nutrients are absorbed by the villi, they enter the bloodstream. Carrier proteins help bring the essential nutrients into the various cells throughout the body.  

Macronutrient and Micronutrient Absorption

Not all nutrients are created equal. While the digestive process is the primary avenue in which the body properly absorbs nutrients, the actual bioavailability of each nutrient varies.

Macronutrients, such as fats, proteins, and carbohydrates, are typically easier for the body to absorb. This makes the bioavailability of macronutrient absorption high. Basically, a nutrient that is high in bioavailability is able to reach its destination and accomplish its goal — in this case, providing energy for the body. 

Micronutrients such as vitamins, minerals, and various phytochemicals are not as easily absorbed. Since they exist in so many different forms, their absorption rate is much harder to predict than macronutrients.

Water-Soluble vs. Fat-Soluble

Vitamins vary greatly in how they’re absorbed, stored, and excreted in the body. However, they are typically classified in two ways: Water-soluble and fat-soluble. 

Water-soluble vitamins are more easily absorbed in the body than fat-soluble vitamins. However, this also means the body does not store water-soluble vitamins in large amounts. Excess amounts are excreted through the urine. 

Fat-soluble vitamins are basically the opposite, this includes vitamins A, D, E, and K.

These are dissolvable in fat and are stored in the tissue. This allows the body to access them at any time. The caution is the fact that you can end up storing more than you actually need. 

Factors That Affect Bioavailability of Nutrients

The absorption rate and the bioavailability of nutrients in food vary from person to person and can be affected by several factors. Here are some of the main factors that could affect nutrient bioavailability:

  • Age
  • Gender
  • Pregnancy
  • Health status
  • Nutrient demands in the body
  • Body composition (such as body fat)
  • How food is processed, prepared, or cooked

The efficacy and bioavailability of dietary supplements and drug formulations also depend on many different factors. 

For example, the rate of drug bioavailability is affected by things like food intake, the physicochemical properties of the drug, dosage form, and a whole host of external/internal factors that are unique to each individual. 

The Bioavailability of Dietary Supplements

While it is ideal to get all necessary nutrition from the food we consume, that is not always the case. In fact, according to nutrition statistics put out by the Center for Disease Control, fewer than one in ten adults in the United States eat enough vegetables and fruits — primary sources for essential nutrients. 

This is one reason why so many people opt for nutritional supplements. The same principle of bioavailability that applies to the nutrients that we consume through our food also applies to those we consume in supplements. 

But there are some differences. For instance, bioavailability typically refers to the percentage of a nutrient that enters the bloodstream, but it can also refer to how much of the nutrient is utilized and stored by the body. 

The absorption rate and bioavailability of the supplements (vitamins/minerals) vary depending on the type, delivery form (capsule, liquid, etc.), and what is taken with. 

Enhancing the Bioavailability of Your Supplements

There are some things that could make a difference when it comes to increasing the bioavailability (i.e. enhancing the absorption rate) of your supplements. Here are a few things to consider: 

Time of Day

Various factors affect the efficacy of nutrients (e.g. metabolism and time of day). For example, supplements like magnesium are best taken at night due to the potentially calming effects. 

Supporting Supplements

Some nutrients are supported by others. For example, piperine is known for its ability to significantly boost the bioavailability of other nutrients. This is why it is often added to curcumin supplements, as it helps raise its bioavailability.  

Take With or Without Food 

Typically, supplements are not tolerated well on empty stomachs. That is why many are to be taken with meals, such as fat-soluble supplements like vitamins A, D, and E.

The Bottom Line

Bioavailability refers to how efficiently and effectively nutrients are absorbed and utilized by the body. This principle applies to macronutrients and micronutrients consumed through food and supplementation. 

The rates of absorption vary from nutrient to nutrient and are heavily influenced by several factors when taken in supplement form. So, when choosing a supplement, here are some things to consider:

  • What is the most absorbable delivery form of this supplement?
  • Does it need to be taken with or without food?
  • What time of the day should it be taken?
  • Can I take these supplements with other supplements? Will it interact with, inhibit, or be inhibited by any other supplements?

At the end of the day, bioavailability is tough to estimate, but being aware of it makes all the difference when choosing the right supplement. 


Healthy Directions Staff Editor