Vitamins were discovered by studying diseases, not by studying health

Price traces vitamin science back to puzzling deficiency diseases — scurvy among sailors, beriberi among people eating heavily processed rice, rickets among children with little sun exposure — that resisted explanation under the era's dominant nutritional theory, which focused almost entirely on protein, fat, and carbohydrate as the only nutrients that mattered. Something else was clearly missing, but no one yet had a name or a mechanism for it.

Researchers eventually identified that minuscule quantities of specific organic compounds, present in unprocessed or varied foods, prevented these diseases entirely, and their absence caused them reliably. This was a genuinely surprising finding at the time: health could hinge on trace substances rather than only the bulk nutrients previously assumed to be nutrition's whole story.

Price's point is that vitamins entered public consciousness as cures for specific, severe deficiency diseases, which is a very different context from how they're marketed and consumed today, mostly by people with no deficiency at all. Vitamins were discovered by curing severe deficiency, not by proving a benefit for people who already had enough.