By Professor Harrison Weisinger
Australians spend billions on vitamins and supplements every year, but according to Melbourne medical practitioner and researcher Professor Harrison Weisinger, many people are overlooking one crucial question: how much of those supplements is the body actually absorbing?
“It’s the bioavailability problem,” Professor Weisinger says.
“A supplement can look impressive on the label and contain the right ingredient at the right dose. But if very little of it gets absorbed and used by the body, the label doesn’t mean much.”
Bioavailability refers to how much of a substance reaches the bloodstream in a usable form. Two supplements may contain the same active ingredient but behave very differently once consumed, depending on how they are processed, formulated and delivered.
“If you ignore delivery, you’re only looking at half the story,” he says.
One of the clearest examples, according to Professor Weisinger, is curcumin—the active compound found in turmeric.
Curcumin has long been associated with anti-inflammatory properties, but standard curcumin is notoriously difficult for the body to absorb. It is poorly soluble in water, rapidly metabolised and quickly cleared from the body, meaning many traditional powders and capsules may result in low absorption rates.
“That is why people often take turmeric for months and feel almost nothing,” he says.
“The issue is not always the ingredient. Often, it is the delivery system.”
Professor Weisinger says improving absorption has become a major focus in supplement development, particularly through technologies designed to help fat- soluble compounds move more effectively through the digestive system.
One approach attracting growing attention is micellar delivery technology, which uses tiny structures called micelles to carry compounds such as curcumin through the gut and into the bloodstream more efficiently.
A 2021 study published by Flory and colleagues found micellar curcumin demonstrated higher bioavailability than several other curcumin formulations tested, including standard curcumin powders and piperine-enhanced products.
Professor Weisinger says the broader lesson extends well beyond turmeric.
“Bioavailability matters for plenty of other nutrients and supplements too,” he says.
Fat-soluble vitamins such as vitamins D, E and K are generally absorbed more effectively when taken with dietary fat, while different forms of minerals like magnesium can vary significantly in absorption. Digestive health, food timing and interactions with other nutrients can also influence how effectively supplements are utilised by the body.
For consumers, Professor Weisinger says it’s worth looking beyond marketing claims and high-dose formulations.
“People love to talk about what is in a supplement,” he says.
“They should talk more about how it gets in.”
His advice is simple: look beyond the number on the label, consider the delivery method and be cautious of products focused purely on potency rather than absorption.
“If something has done nothing for months,” he says, “ask whether the problem is the formulation, not the ingredient.”
Ultimately, he believes consumers should be asking a different question when choosing supplements.
“The useful question is not, ‘What is in this supplement?’” he says.
“It is, ‘How much of this will my body actually absorb and use?’”
General advice only: Speak with your doctor before starting any new supplement, especially if you have a chronic condition or take prescription medication.
