What is Bioavailability? Five Factors to Consider When Taking Vitamin Supplements

Have you ever had a friend or family member recommended a supplement to you, telling you they’ve experienced amazing results from it? Then next time you’re at the supermarket, you remember their recommendation and pop a bottle in your trolley.

If you don’t feel any immediate benefits from taking a food supplement, you’d be forgiven for thinking it isn’t working.  However, the reasons behind why some food supplements have amazing results for some people but do very little for others are many, and quite complex. An important aspect of effectiveness relates to  ‘bioavailability’ or more simply, how absorbable something is. In this article we’re going to break down this scientific subject, as well as some other factors to bear in mind when considering which supplements to take. 

Illustration of nutritional processes

You Are What You Absorb

We’re all aware of the saying “You are what you eat” but in reality it is more accurate to say “You are what you absorb”. Bioavailability is how well a substance, such as a nutrient or medicine, gets into your bloodstream. When we eat or drink, our bodies are very efficient at taking the nutrients into our bloodstream and then they’ll either choose to use, store or get rid of them. Macronutrients are the nutrients we need in large quantities to provide us with energy i.e. proteins, fats and carbohydrates, and these are usually very well absorbed by our bodies. Micronutrients, on the other hand, are only required in small amounts, but they are still essential for us to function properly. Certain ones can be harder for our bodies to absorb, such as magnesium, or iron from plant sources.

When packaged up as a food supplement, if these nutrients are not bioavailable, that is, present in  an absorbable formulation or taken with the right substance to help absorption, then they will simply not reach enough levels in the body to be able to do their job.

Illustration of nutrients moving within the gut

Take for example curcumin, the active ingredient in turmeric. It is a fat soluble substance, so if it is not taken with a meal that contains fat it will not be  absorbed as well by the body. Similarly, for a turmeric food supplement to be properly absorbed, it needs to be combined with ingredients that can help its absorption, such as lecithin (a type of fat) or black pepper.

Nutritional scientists fundamentally understand the importance of bioavailability. So when they’re developing supplements and vitamins, they know that one of the key considerations when creating a proven formula that delivers benefits is - you’ve guessed it - bioavailability.

What Else Can Affect Bioavailability?

Without getting too deep into the science, there are many factors that can affect bioavailability.

These factors include:


  • The method by which the substance is administered i.e. if you have an intravenous drip of a substance, it will be far more bioavailable than a tablet.
  • Nutrients that are fat soluble, such as vitamin D, will be better absorbed if they are eaten with a meal, as most meals contain a significant amount of fat (oils, butter, milk etc).
  • Digestive health - conditions that affect your gut (such as IBS), or the amount of  acid produced in the stomach can, in turn, affect absorption of certain nutrients.
  • Interactions - certain substances can help or hinder absorption. For example iron should not be taken with drinks that contain tannins (such as coffee or tea) as it can affect absorption negatively. On the other hand,  taking iron with orange juice can aid absorption, as it contains vitamin C.
  • The ageing process - As we get older, absorption in the gut becomes less efficient, so it becomes harder to get all the nutrients we need from food.


Illustration of divided plate showing fats, carbohydrates and proteins


Is Bigger Always Better?

You would be forgiven for thinking that the higher the dose of a supplement you take, the better it will be for you. It can be very tempting to go for a tablet that boasts say, 1,000mg of vitamin C, for example. Surely taking a higher dose guarantees getting more of the goodness straight into your body. This is not always the case.  With this particular nutrient, your body will take only what it needs and then discard the rest. So if you’re already following a healthy diet which already includes lots of vitamin C, you probably don’t need such a high strength supplement.

If the supplement hasn’t been developed in a highly bioavailable formulation, the chances are your body will simply excrete what it doesn’t need and you will feel very little benefit. So, if you have two types of the same supplement containing different amounts of the main ingredient - let’s say formulation A has 500mg of magnesium and formulation B has 125mg. The first is a standard form of magnesium, the second one is 5x more bioavailable. So, in this case, the second formulation will be equivalent to taking  625mg of magnesium from the first formulation; so considerably more than the first. This is important as certain nutrients like magnesium, if taken in high amounts, can cause some undesired gastrointestinal side effects.

Isn’t It Better to Just Eat Lots of Fruit and Vegetables, than Having a Supplement?

In an ideal world we would get every macro and micronutrient in exactly the right amounts from our diet. Whilst many of us do follow what we’d consider a healthy, varied, balanced diet, abundant with fresh fruit, vegetables, lean proteins and good fats, we may still be missing out on vital nutrients. This is due to several factors:


  • Eating vegetables and fruit that is out of season - they will generally not have the same nutrients as food grown in season.
  • If you follow a restrictive diet, such as a vegan diet, nutrients such as iron and B12 will be difficult to obtain through plant sources alone.
  • Our body’s ability to absorb nutrients from foods - i.e. the ageing process can impact this.
  • The amount of a certain food we’d need to eat to meet our requirements.


Illustrated plate showing wheel of different vitamins and minerals


Let’s take the substance lycopene that is found in tomatoes and gives them their bright red colour. It’s hard for our bodies to absorb lycopene from raw tomatoes alone, lycopene is better absorbed  after the tomatoes  have been cooked in fat or oil. Tomato sauce is a good source of lycopene, but because we tend to have it with fatty foods such as pizza or fries, we’ve undone all its goodness. A lycopene supplement could help, but as lycopene on its own is not well absorbed, it won’t do us much good unless it’s taken from a bioavailable formulation. A supplement that combines lycopene with whey protein has been shown to have better absorption than standard lycopene, and one daily dose (in form of capsule) provides the same amount of lycopene you would get from eating 1kg of cooked tomatoes per day!

So the next time you’re in the market to try a new supplement, it pays to do some research into the different kinds available. Take a look at how the vitamin or food supplement has been formulated, if it is bioavailable and what other ingredients have been combined. Many supplements now come in a form that can be made into a drink, which for many is a much better way of taking them.



Click here to find more information on bioavailability from FutureYou Cambridge.

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