What is bioavailability? We often hear this term thrown around when it comes to biohacking and supplementation, but what on earth does it mean and why does it matter?
Simply put, bioavailability refers to the fraction of a nutrient or medicine that can be absorbed into the body to be used — in the chemical activities of the body’s cells, or in structures such as muscles and bones.
When you swallow a supplement, drink a herbal tonic or rub a herbal cream onto your body, active components such as vitamins or herbal constituents need to be absorbed into your body before they can work. If they can’t be absorbed, they will have little to no effect.
When you take medicine orally, substances are moved by the contraction of muscles in your digestive tract (known as peristalsis) from the mouth and throat into the gastrointestinal tract. In the stomach and small intestine, digestive acids and enzymes break the compounds of the medicine or vitamin down into smaller fragments.
Of these, water-soluble compounds such as vitamin C are taken up by the intestinal cells and then released into the bloodstream. Fat-soluble compounds such as Omega-3 fatty acids are taken up by lymph nodes, which carry lipids into the lymphatic circulation. The amount or proportion of these unique compounds absorbed is referred to as bioavailability.
Water-soluble particles are easily absorbed, while the lymphatic system deals with fat-soluble lipids easily. Ingredients that are poorly soluble — i.e those that don't break down in fat or water are very poorly absorbed.
In summary, some components are more easily absorbed than others, making them more bioavailable.
Once a nutrient or medicine is taken into the body, cells may break it down, pump it straight back into the digestive tract, or release it into the bloodstream.
From there it is carried directly to the liver, where it may be metabolised (broken down), activated, or inactivated by the liver cells. This is known as first-pass metabolism.
And finally, the liver may simply eliminate the compound by secreting it into bile, which is then carried back to the intestine for excretion. All these factors affect bioavailability.
Therefore to be highly bioavailable, an ingredient needs to be efficiently absorbed and remain in the body in an active form long enough to have an effect.
Iodine is an essential nutrient. This trace mineral is very water-soluble, is easily dissolved and is almost 100% absorbed. This is a highly bioavailable nutrient.
Magnesium, also an essential element, is absorbed from food at a rate of 30-40%. In supplements, magnesium oxide is poorly soluble and bioavailability is only 15%.
Studies have found that magnesium in the aspartate, citrate, lactate and chloride forms is absorbed more completely, and is more bioavailable than magnesium oxide and magnesium sulphate.
Now as important as improving bioavailability is, it is also important to understand what can inhibit bioavailability. Strap in for a quick crash course in science!
• Insoluble compounds. For example, magnesium citrate is water-soluble, but magnesium oxide is much less so. The insoluble oxide form reduces absorption. Soluble minerals are preferred in dietary supplements.
• Large molecules. Polyphenols, for example, are the most abundant bioactive phytochemicals in the human diet (think berries, coffee and cocoa), but their bioavailability is extremely low: only 1-10% due to their relatively large molecular size.
• Food binders. Phytic acid in legumes, grains and rice binds to essential minerals and reduces their absorption.
• Poor digestion. There are many factors that drive the efficiency of the digestion and absorption processes. These include a person's unique metabolism and characteristics of the food being digested. In essence, poor digestion drives poor bioavailability.
• Gastrointestinal dysbiosis, or an overgrowth of nasty gut bugs. For example, healthy microbiota (healthy gut bugs) produce the enzyme phytase, which releases essential minerals from phytate in the food. Without a healthy microbiome, this will not occur and you will not be able to release nutrients from certain foods.
• Tea and coffee. These beverages contain polyphenols which markedly reduce the absorption of plant-based iron.
• Fibre supplements. Large doses of fibre supplements can reduce the absorption of calcium, magnesium, zinc, vitamin B12 and potentially other nutrients if taken at the same time. The fibre should be taken at least half an hour before a meal or by consuming supplements so that it doesn't impact absorption.
• Alcohol. Excessive alcohol consumption reduces the bioavailability of many nutrients including biotin, folate, other B vitamins, vitamin A, lutein, and zeaxanthin. This can be due to reduced absorption, poor digestive function, increased urination, increased bowel movements, or all of these. When this is the case, additional supplementation is recommended. Excessive alcohol consumption may also unfavourably alter the microbiome of the digestive tract. This is where replacement probiotic supplements can support a healthy microbiome.
There are several methods that increase the bioavailability of nutrients in your body. Here are our top suggestions:
To enjoy optimum bioavailability of foods, medicines and supplements, you need a healthy digestive system, alongside a varied, balanced and whole food diet. Effective digestion requires a healthy microbiome, which needs regular consumption of prebiotic foods such as soluble fibre, dairy foods and fermented foods as well as probiotic bacteria such as in yoghurt.
Where fibre supplements are necessary — supplements should be soluble fermentable fibre, rather than insoluble. Sources of soluble fibre include oat bran and psyllium. Fibre supplements should be taken at least half an hour before meals or other supplements and medicines, to avoid interfering with absorption.
Nutritional supplements are best taken with food as the digestive system is active, increasing the digestion and absorption of nutrients.
Meals should include spices such as pepper and ginger, to enhance the bioavailability of all nutrients.
Moderation in consumption of tea, coffee and alcohol is recommended, as it can impact the absorption of vital nutrients.
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*Always read the label and follow directions for use. If you experience any symptoms or if symptoms persist, talk to your health professional. Vitamin and/or mineral supplements should not replace a balanced diet.