You're probably not absorbing what's on the label

The supplement drawer in most households tells a familiar story: capsules, tablets, softgels, a monthly spend somewhere north of £50 that continues on the quiet assumption that if the label says '500 mg', then 500 mg is what the body receives. It rarely is.

Between swallowing a capsule and a nutrient reaching a cell in usable form sits a gauntlet of chemistry — stomach acid, gut-wall permeability, liver processing, transporter competition — that can reduce what actually enters the bloodstream to a fraction of what the packet declares. This fraction has a name: bioavailability, defined as the proportion of an ingested compound that reaches systemic circulation in active form.

In Practical Regeneration, Professor Paul Lee places this problem at the heart of his Chemistry pillar, arguing that delivery method is not secondary to ingredient content — it is co-equal with it. The body's internal environment, he contends, is the invisible determinant of whether any nutrient does its job. The science behind that claim is more concrete, and more actionable, than most supplement labels let on.

What bioavailability actually measures

Think of bioavailability as the gap between the dose on the label and the dose the body can actually use. Pharmacologically, it is defined as the fraction of an ingested compound that enters systemic circulation in active form — with intravenous delivery set at 100% as the reference standard, because it bypasses every barrier between bottle and bloodstream.

Four variables determine where any oral supplement lands on that scale.

Chemical form is often the deciding factor at source. The same mineral can exist in several configurations with dramatically different absorption profiles — a distinction that operates before a compound even reaches the gut wall.

Solubility determines whether a compound can cross the intestinal lining at all. Fat-soluble molecules — vitamins A, D, E, K, and CoQ10 — cannot pass through the gut wall without first being incorporated into micelles, tiny transport structures that require adequate dietary fat to form. Without fat in the meal, absorption may fall sharply regardless of the stated dose.

Transport mechanism governs the route through that wall: passive diffusion, active carrier proteins, or micelle-mediated uptake via the lymphatic system. Each route has its own saturation ceiling and is vulnerable to different interference patterns.

Hepatic first-pass metabolism intercepts what does get absorbed. Compounds drawn from the gut enter the portal vein and travel directly to the liver, where hepatic enzymes may break down a significant proportion before anything reaches general circulation — making the liver less a villain than an unavoidable checkpoint.

Critically, none of these variables is fixed. Each shifts with gut health, microbiome composition, and what else happens to be in the meal — which means two people swallowing the same capsule at the same dose may end up with measurably different circulating concentrations. Understanding which of these variables you can influence is where the practical conversation begins.

The barriers between pill and cell

Swallowing a capsule sets off a journey with several checkpoints — and at each one, losses mount.

Gastric acid is the first. At a pH of roughly 1.5 to 3.5, the stomach is a hostile environment for many compounds: certain B vitamins, plant extracts and enzyme-sensitive forms begin to degrade here, well before the small intestine where absorption principally occurs. Fat-soluble nutrients face a related but distinct problem: without dietary fat in the same meal, there is insufficient bile stimulation to form the micelles that carry vitamins A, D, E and K across the gut wall — so timing and meal composition both affect the dose that actually arrives.

At the intestinal wall itself, other contents of the meal intervene. Phytates in wholegrains and legumes, and oxalates in spinach and certain nuts, bind to minerals — iron, calcium, zinc, magnesium — forming insoluble complexes that the intestinal lining cannot absorb. Label milligrams and bioavailable milligrams can diverge quietly in every high-fibre meal.

Transporter competition adds a further constraint. Calcium, magnesium, iron and zinc share a limited pool of carrier proteins in the gut wall; taken together at the same moment, each reduces the others' uptake rate.

Absorption capacity also shifts across a lifetime. Gastric acid output tends to decline after middle age, carrier-protein efficiency changes, and the gut microbiome — which influences how nutrients are processed prior to absorption — differs substantially between a person's 30s and 60s. A labelled dose that was adequate at one life stage may reach systemic circulation in meaningfully lower concentrations a decade or two later.

Knowing where in that sequence things go wrong is the prerequisite for making formulation choices that work with the body's chemistry rather than against it.

Chemical form is where most supplements fail or succeed

Two products can list the same ingredient in the same milligram quantity and produce completely different results in the body — and the reason usually comes down to a single word printed after the slash on the label.

Consider magnesium. Magnesium oxide, the form found in many high-street products, has a fractional absorption of approximately 4% — the unabsorbed majority remaining in the intestines, where its osmotic effect may simply accelerate gut transit rather than replenish any cellular deficit. Magnesium glycinate, in which the mineral ion is chelated — chemically bound — to the amino acid glycine, absorbs through dipeptide transport pathways with fractional absorption reaching approximately 80% and measurable serum concentrations within three to five hours. The elemental dose may appear identical on both labels; the systemic dose differs by a factor of roughly twenty.

A chelate does something structurally elegant: it wraps a charged mineral ion in an organic molecule, effectively disguising it from the intestinal environment that would otherwise strip it away before transport.

The curcumin story illustrates a different chemistry altogether. Turmeric's active compound is rapidly inactivated by glucuronidation enzymes in the liver and gut wall, leaving blood concentrations that are often undetectable after a standard oral dose. Research suggests that co-administering approximately 20 mg of piperine — the alkaloid responsible for black pepper's heat — inhibits those same enzyme pathways, raising curcumin bioavailability by up to 2,000%. No change to the curcumin itself; a targeted change to the enzymatic environment that determines its fate.

Inorganic salts — oxides, sulphates, carbonates — cost less to manufacture and dominate mass-market shelves precisely because the milligram figure on the front panel looks the same as any other. The practical implication is straightforward: the chemical form listed after the slash is, in many cases, more consequential than the number in front of it.

Cofactor chains — when one nutrient depends on another

The vitamin D story is a useful illustration of how even well-absorbed nutrients can fail to deliver — not because they never reached the bloodstream, but because subsequent steps in the chain were missing.

Vitamin D is fat-soluble and, as already described, relies on micelle formation for gut-wall absorption — meal composition matters at the point of ingestion. But once absorbed, the story continues. The body must enzymatically convert vitamin D into its biologically active form, calcitriol, in the liver and kidneys; that conversion requires magnesium as a cofactor. Where magnesium status is insufficient, supplemental vitamin D may remain largely inactive regardless of the dose taken.

Calcitriol, once produced, drives calcium absorption from the gut. A further dependency then surfaces: vitamin K2 is needed to direct that mobilised calcium towards bone rather than allowing it to accumulate in arterial walls. Without adequate K2, calcium shifted by an optimised vitamin D protocol has no reliable routing mechanism downstream.

One practical point worth noting when choosing a combined supplement: calcium and magnesium share overlapping intestinal transport mechanisms, and high calcium doses can suppress magnesium uptake — the same mineral required to activate the vitamin D taken in the same breath.

What this sequence reveals is that 'am I taking enough vitamin D?' is only half the question. The more useful framing, which Professor Paul Lee develops in Regeneration by Design, is whether the whole activation chain — absorption, enzymatic conversion, downstream routing — is adequately provisioned. That is a systems question, not a dosing one.

What better delivery actually looks like — and what to do this week

Liposomal formulations represent the most practically accessible upgrade from standard capsules. By encasing nutrients in phospholipid vesicles that mimic cell membrane structure, they resist gastric acid breakdown and route absorption through the intestinal lymphatic system rather than the portal vein — largely sidestepping first-pass hepatic clearance. Clinical data for liposomal vitamin C record an area-under-curve approximately 1.79 times greater than standard oral forms. That uplift is most meaningful for compounds that are inherently fragile in the gut or rapidly cleared by the liver; for already well-absorbed nutrients, the premium may matter considerably less.

A necessary caveat applies to novel delivery formats in general: the UK Committee on Toxicity noted in December 2025 that marketing claims for liposomes, micelles, and emulsions frequently outpace the clinical evidence behind them, with toxicological effects at higher effective doses still poorly characterised. The practical dividing line is between well-studied chemical forms — magnesium glycinate, methylfolate, calcifediol — where absorption data are robust, and branded "enhanced-delivery" products where independently cited evidence is absent. When a label claims superior bioavailability but cites nothing, the standard well-characterised form is usually the sounder choice.

For those seeking to eliminate oral absorption variability altogether, intravenous delivery bypasses every barrier discussed across this article: solubility limits, first-pass clearance, transporter competition, meal timing. The Regen365 protocol within the Regen PhD ecosystem operates on this principle — a clinically administered wellness option, not a daily supplement alternative, for anyone asking how close to full cellular delivery is actually achievable.

Four things to action this week:

• Read beyond the milligram number: glycinate or citrate forms for minerals consistently outperform oxides; methylfolate is more reliably absorbed than folic acid where relevant.
• Take fat-soluble vitamins (D, K2, E, A) with a meal containing fat — micelle formation in the small intestine depends on it.
• Pair vitamin D3 with magnesium and K2 to support the full activation and downstream routing chain covered in the previous section.
• When paying a premium for "enhanced bioavailability," ask for an independent cited study; if none is provided, the standard well-characterised form is usually the better buy.

The Chemistry pillar asks not just 'what am I taking?' but 'what is my body actually receiving?' — the distinction Practical Regeneration frames as the threshold between passive supplementation and deliberate nutritional design.

Before adjusting your supplement regimen, speaking with a qualified healthcare professional is advisable, particularly where prescription medications or underlying health conditions are involved.

1. [1] Bioavailability — Wikipedia. https://en.wikipedia.org/?curid=769021 https://en.wikipedia.org/?curid=769021