It’s not just the type of vitamin you take that’s important; it’s how you take it.
That’s right. Certain methods of taking vitamins are better absorbed by your body than others. This absorbability is determined by a number of factors, but one of the most important of these factors is bioavailability.
We break down what bioavailability is, what it means when taking supplements, and how to choose supplements that will make the most impact for you.
The standard form for taking vitamins and supplements is oral. That’s gummies, pills, tablets, and even powders. This is the standard because they’re fairly easy to consume, and are the most easily found in stores.
Yet various studies show that oral supplements are not as efficacious compared to other forms of supplements.
That’s why bioavailability is so important in understanding what a supplement's dosage really means.
What is bioavailability?
When you take a supplement, not all of it is absorbed by your body. With most supplements, a large fraction never even enters systemic circulation because it’s broken down, or metabolized, before it can be used by your body.
Systemic circulation refers to the movement of blood from your heart to the rest of your body. Your bloodstream carries oxygen as well as other nutrients and substances (like supplements) to be used by those parts of the body.
In regards to supplements, bioavailability refers to the remaining amount of a substance that successfully reaches systemic circulation. This fraction is what gets actually absorbed vs. what was ingested. This remaining portion is what gets used by your body.
The necessary dose of a drug is indirectly proportional to its bioavailability.
When something has high bioavailability, a high percentage of the amount is absorbed by the body. A supplement with high bioavailability does not require a large dose to reach a minimum effective concentration.
When something has low bioavailability (poor), the amount that is properly absorbed by the body is very low. A supplement with low bioavailability requires a larger dose to reach a minimum effective concentration.
What this means: if your supplement is highly bioavailable, you don’t need to take as much as you would have otherwise with a supplement that has low bioavailability in order to get the same effect.
What impacts bioavailability?
In pharmacokinetics, the study of drug movement through the body, the route of administration (ROA) is the way a drug is applied.
ROA is determined by the location of application; for example, oral supplements are consumed. Intravenous supplements are injected directly into your bloodstream via IV. An intranasal supplement is absorbed through your nose, or nasal passage.
Depending on this ROA, the drug's properties and design differ. This, as well as the dose of a drug, impact the rate and extent of a drug's bioavailability.
Essentially, the different ways supplements enter your body affect how bioavailable– how efficiently absorbed– the supplement is.
An intravenously delivered substance (IV) is assumed to immediately enter systemic circulation. It does not require consideration of absorption or first-pass metabolism to determine adequate dosage. By definition, an intravenously administered substance’s bioavailability is 100%.
On the other hand, an oral supplement passes through the gastrointestinal (GI) system, where it’s exposed to intestinal absorption and hepatic first-pass metabolism before it’s absorbed. This method typically has a much lower bioavailability, as low as 15%.
You can see how the same dosage amount, taken in different ways (oral vs. IV), would result in very different effects. Therefore, changing the route of administration requires a change in dosage.
Why oral supplements have low bioavailability
Insufficient time for absorption in the gastrointestinal (GI) tract is a common cause of low bioavailability.
Orally administered substances must pass through the intestinal wall and the liver; both are common sites of first-pass metabolism (metabolism that occurs before a substance reaches systemic circulation).
Because of this first-pass effect, substances’ concentration is significantly reduced.
Supplements that do not have to pass through the GI tract do not experience this issue. That’s why in studies with melatonin supplements, oral supplements had far poorer bioavailability compared to intravenous methods and intranasal methods (sleep sprays).
In fact, intranasal supplements in various drug studies tend to yield significantly higher bioavailability than their oral counterparts.
In the case of melatonin, more than 80% of oral melatonin gets metabolized before it’s absorbed, resulting in its poor bioavailability. Not only that, because it takes time for your body to break down and absorb oral melatonin, it can take up to an hour or more for oral melatonin to take effect.
There’s still variability among different types. A clinical study compared vitamin D3 as either a single gummy or tablets; it found that the gummies had greater bioavailability than tablets and led to higher vitamin D concentrations over time.
How to select bioavailable supplements
Oral supplements in general tend to have much lower bioavailability. Research your other options to avoid low bioavailability supplements.
For example intranasal absorption is one such option that is available for a number of supplements.
Intranasal supplements (nasal sprays)
Supplements like nasal sprays are absorbed through the nose. Your nasal cavity contains structures that are highly permeable and porous, which allow rapid transportation of a substance via molecular diffusion. By going through the nasal cavity, you bypass the typical physiological barriers such as the blood-brain and blood-cerebrospinal fluid barriers that slow absorption to the brain and bloodstream.
Intranasal application offers a more direct pathway to your brain, bypassing any barriers that would delay it from being absorbed such as first pass metabolism.
A study comparing methods of absorption for melatonin found the greatest potential in intranasal absorption, which was absorbed much more quickly compared to other methods including oral and transdermal melatonin.
You can see why nasal supplements like Ascent Sleep, which is almost more than 90% absorbed by the body, might be an alternative to your standard melatonin gummies.
Transdermal supplements (skin patches)
Skin patches and topical solutions applied on the skin are considered transdermal supplements, and are absorbed through the skin. Transdermal absorption similarly allows you to bypass the first-pass effect that affects oral supplements. This can mean there’s improved bioavailability through this method.
There are limited factors, however. Transdermal administration requires hydrophobic substances, restricting the type of substances or medications that would yield good results from this method.
What supplements to take
When it comes to choosing supplements, there’s always a recommendation to take such and such vitamins to support such and such functions; Vitamin D for our immune system, calcium for bone strength, magnesium for mood regulation, fish oil for cholesterol, and the list goes on.
While those vitamins and minerals can be found in the foods we eat, taking supplements can help us avoid potential deficiencies in our diet.
It should be noted that supplements are intended to supplement your nutrient needs, not replace them. Taking vitamin or mineral supplements can help support an aspect of your health, but you should still be consuming a varied, balanced diet.
Other factors that influence absorbability
Taking other vitamins and minerals might influence the absorbability of a supplement.
For example, taking vitamin C helps absorb iron. There is also the opposite, where taking one type of vitamin or mineral might compromise absorption of another.
For example, it’s usually recommended not to take calcium and zinc at the same time, as they are commonly stated to compete for the same absorption sites.
Taking vitamins with fats
This is more specific to oral supplements. Low bioavailability is most common with oral dosage forms of poorly water-soluble, slowly absorbed substances. There are a number of vitamins that are absorbed in a manner similar to that of fats, making them more easily transported when taken with fats.
Some fat-soluble vitamins include Vitamin A, D, E or K.
Other factors include
- Your sex, age, or general health conditions
- Your overall diet
- Having microbiome imbalances (your gut health)
- Conditions that inhibit nutrient absorption