People usually describe deficiency as feeling persistently depleted in a way that rest does not fix. That description is accurate but not diagnostic, because it fits many conditions that have nothing to do with nutrition.
The B12 pattern
NIH ODS lists fatigue, palpitations, pale skin, glossitis of the tongue, weight loss, and neurological changes including numbness and tingling in the hands and feet. The tongue symptom and the pins-and-needles sensation are the more distinctive parts.
NIH ODS also notes symptoms "can take several years to appear" — so the onset is gradual enough that people often normalize it.
The iron pattern
NIH ODS describes effects on gastrointestinal function, immune function, and body temperature regulation. Feeling cold when others are not is a frequently reported experience that maps onto that last one.
The vitamin C pattern
NIH ODS describes scurvy as fatigue, widespread connective tissue weakness, and capillary fragility — which is why easy bruising and bleeding gums appear in descriptions.
The vitamin A pattern
NIH ODS identifies night blindness as the first sign — specifically difficulty seeing in low light. This is one of the few genuinely specific deficiency symptoms.
Why the overlap is the whole point
Four different nutrients, and fatigue appears in three of the four lists. Anyone reasoning backwards from "I am tired" to a specific nutrient is working from the least informative symptom available.
What helps a clinician is the pattern: which symptoms, how long, alongside what dietary and medication circumstances. That is a description worth bringing to an appointment.
Our free assessment organizes exactly that.
References
This article summarizes published guidance from the sources linked above. It is general information, not medical advice, and it cannot tell you whether you personally have a deficiency. Only a clinician ordering the right test can do that. If you have symptoms that concern you, speak to a doctor.