Not All Vitamins Are Created Equal
The 13 essential vitamins divide into two fundamentally different categories based on their solubility. Fat-soluble vitamins (A, D, E, K) dissolve in lipids and can be stored in body fat and liver for months. Water-soluble vitamins (C and the eight B vitamins) dissolve in water, are not significantly stored, and excess is excreted in urine within hours. This distinction determines everything about how they should be consumed.
The Micelle Gateway
Fat-soluble vitamins cannot cross the intestinal wall alone. They must first be incorporated into micelles — tiny spheres of bile salts and dietary fat that form during digestion. Without adequate fat in a meal, micelle formation is insufficient and most of the vitamin passes through the gut unused. Studies show that taking vitamin D with the largest meal of the day (which typically contains the most fat) increases absorption by 50% compared to taking it on an empty stomach.
Nutrient Competition and Synergy
Vitamins and minerals do not exist in isolation — they interact in complex ways at the absorption site. Iron and calcium compete for the same transporters, so taking them together reduces absorption of both. Conversely, vitamin C enhances non-heme iron absorption by up to 6-fold by reducing ferric iron to the more absorbable ferrous form. This simulator models these interactions through competition and synergy factors.
Optimizing Your Supplement Strategy
The difference between optimal and poor supplement timing can be a 3–5x difference in actual absorption. Take fat-soluble vitamins with meals containing fat. Separate competing minerals by at least 2 hours. Take iron with vitamin C but away from calcium and coffee. Water-soluble vitamins are best taken in divided doses since excess is rapidly excreted. This simulation helps quantify these effects so you can make evidence-based decisions.