The Bioavailability of Supplements


Recommending supplements is a part of helping to ensure the overall health and wellness of patients. Understanding that may impact a patient’s ability to absorb supplemental nutrients, however, can become a complex array of factors to consider. In looking at nutritional supplementation, a practitioner should be concerned with how much of a nutrient can be absorbed, and how much of that nutrient is available for cellular uptake, use, or storage. 1


Considerations affecting bioavailability include the physical properties of a supplement, such as hydrophobicity, solubility, and binding agents, all of which may influence absorption. Methods of formulation and encapsulation can also affect absorption—is a supplement time-released? Extended release? Solubility also appears to influence absorption, such as with vitamin C and mineral salts, wherein being water-soluble they are rapidly absorbed. Smaller doses (with the exception of vitamin C) have been shown to increase the percentage of nutrient absorbed, however, this does not affect absorption within the gastrointestinal tract. 2 Mineral salts such as zinc, are absorbed in a secondary phase of absorption within the intestine. 2


What of nutrients utilizing emulsification technology? Vitamin E, in softgel format, may compete with a vegetable-based vehicle, 2 thereby reducing bioavailability. In contrast, emulsification may facilitate bioavailability because the body must produce a protein-bound form of the nutrients in order to be compatible with transport into the serum. 2


Additional factors include the presence and content of other nutrients. For example, vitamin c improves absorption of iron; vitamin D improves calcium absorption; and fat soluble carotenoids see enhanced bioavailability with the addition of fat. 2 Inhibitors of absorption include oxalates like those found in spinach, as well as phytates found in plant-foods such as oatmeal, that can slow the absorption of minerals. 2


Dosing also plays a role. In larger doses, the bioavailability of certain nutrients decreases. 3 Zinc is an example of this, wherein an increase in concentration results in a decrease of efficiency in which zinc is absorbed. 3 This may not necessarily be deleterious for overall levels of zinc, as the process has been shown to be executed by the body to achieve homeostasis. 3 This scenario is also seen with vitamin B 12 , as well as calcium, wherein the body performs processes to keep the absorption of these nutrients regulated. 3


The microbiome also plays a large role in nutrient absorption, with certain gut microbes contributing to the synthesis and bioavailability of vitamins.(CITE Pressman) Vitamins synthesized in the gut often do not resemble their dietary forms, and human gut variability, including metabolic processes involving microflora, are large variables where bioavailability is concerned. 2


Taking into account the multitude of factors that can affect nutrient bioavailability, together with an individual patient’s general gastrointestinal tract health, acute or chronic illness status, pregnancy, athletic or nutritive status, age extreme (elderly, pediatric), and genetic makeup, 2 a more effective supplement regimen may be made.



1. Srinivasan VS. Bioavailability of nutrients: a practical approach to in vitro demonstration of the availability of nutrients in multivitamin-mineral combination products. J Nutr 2001;131(4):1349S-1350S.

2. Pressman P, Clemens RA, Hayes AW. (2017). Bioavailability of micronutrients obtained from supplements and food: A survey and case study of the polyphenols. Toxicology Research and Application.

3. Hambidge KM. Micronutrient bioavailability: Dietary Reference Intakes and a future perspective. Am J Clin Nutr. 2010;91(5):1430S-1432S. doi:10.3945/ajcn.2010.28674B