The supplement aisle is built on a simple pitch: if a little helps, a lot must help more. Labels shout 5,000 IU, 1,000 mcg, mega, extra-strength. That logic works for shoes and bandwidth. It does not work for nutrients.

Most vitamins and minerals follow a U-shaped curve. Too little and you get deficiency. A band in the middle is where the body works well. Past that band, extra dose does not buy extra health. It buys waste, then interference, then harm. The industry sells the right-hand slope as "optimisation." Your liver, bones, hair, and unborn child do not read the marketing.

What "more" actually does

Water-soluble vitamins (B-complex, C) are the friendliest version of this. The body keeps a small working pool and dumps the rest. Neon-yellow urine after a high-dose B-complex is mostly unused riboflavin leaving. It is not proof the pills are "working." It is a receipt for what you paid for and did not keep. Absorption itself is dose-dependent: as the swallowed amount climbs, the fraction absorbed often falls. You spend more to move a little more across the gut wall, and a lot more into the toilet.

Some nutrients do not just leak out. They trigger gates. A large oral iron dose raises hepcidin, which then blocks the next dose for many hours. Mega-dosing daily can be less efficient than a smaller amount on alternate days. The body is not a bucket. It is a set of transporters and feedback loops. Flooding them does not override the locks.

Form matters more than the number on the bottle. Organic magnesium salts generally absorb better than cheap oxides. Poorly soluble curcumin powder is almost a tourist in the bloodstream; a better delivery form of the same molecule reaches more tissue at a lower dose. "Potency" that never arrives is just expensive dust.

When more is not waste, it is poison:

Fat-soluble vitamins and several trace minerals are stored. They do not flush as politely as riboflavin. Vitamin A (preformed retinol, not carrot beta-carotene) is the textbook case. The adult RDA is on the order of 700–900 mcg RAE. The tolerable upper intake level for preformed vitamin A is 3,000 mcg (10,000 IU) a day from supplements and fortified foods combined. Chronic intake above that can cause headache, skin peeling, liver injury, bone thinning, and raised intracranial pressure. In pregnancy, high supplemental retinol is teratogenic; the usual caution is to stay well below 10,000 IU from pills alone. Liver, cod liver oil, and a high-A multi stacked together can get there without anyone noticing. Beta-carotene from plants is a different story: conversion is regulated, so you get orange skin long before classic vitamin A toxicity. Preformed A is not.

Selenium is even tighter. The RDA is 55 mcg. The UL is 400 mcg. Selenosis, hair and nail brittleness or loss, garlic breath, GI upset, fatigue, neurological symptoms, shows up with chronic excess. A single Brazil nut can deliver a full day's requirement. A "thyroid support" or "antioxidant" stack at 200 mcg on top of nuts, a multi, and seafood is how people drift over the line. There was also a real outbreak when a liquid supplement was manufactured at about 200 times the labelled selenium dose; hundreds of people got sick. That was a factory error, but it only happened because people assumed a bottled mineral was automatically safe at whatever the label implied.

Other familiar examples sit on the same curve: high-dose vitamin E associated with higher bleeding risk and, in some trials, worse outcomes; excess zinc crowding out copper; high-dose niacin flushing and liver strain; too much folate masking B12 deficiency; vitamin D megadoses driving calcium into the wrong places if K2 and magnesium status are ignored. SELECT found that men who already had high selenium status and then supplemented had a higher prostate-cancer signal. Antioxidant megadoses have failed, and sometimes harmed, in large prevention trials. The pattern is consistent: the sweet spot is not "as much as the bottle allows."

Numbers are easy to print. "10,000 IU" looks twice as serious as "5,000." Absorption, timing, form, and interactions do not fit on a front label. Stacking a multi plus hair, immune, eye, and "detox" products is how ordinary people exceed upper limits without ever taking a single "toxic" pill on purpose. Fortified cereals and energy drinks add another silent layer.

Food rarely does this. You would have to live on liver and Brazil nuts. Pills and liquids can.

A saner rule:

1.Fix a documented gap (labs, diet, pregnancy, restricted eating).

2.Count all sources of the same nutrient before adding another bottle.

3.Prefer forms the gut can use, at doses near the RDA unless a clinician has a reason to go higher and a plan to stop.

4.Treat upper limits as real, especially for preformed vitamin A, selenium, iron, and high-dose fat-solubles.

5.If urine is neon and the bottle is "mega," you are funding a very expensive filtration project.

The Mercola newsletter that sparked this article (link below), is right on the narrow point: bigger labelled doses often mean more waste, and form beats swagger. It underplays the sharper point. For several nutrients, more is not merely inefficient. It is the other side of the same U. Deficiency and toxicity are neighbours. The marketing lives in the gap between them and hopes you never notice the cliff.

https://takecontrol.substack.com/p/sep-19-2026-take-control-nl?