Why this page comes before the product pages
A supplement sold for general support in healthy adults is the wrong answer to a deficiency. If something specific is missing, replacing that specific thing is both cheaper and far more likely to work. Ruling it out costs one appointment.
Vitamin B12
The most important one on this list, because it is common, it genuinely affects cognition, and it is easy to miss. Absorption declines with age. It declines further on metformin, and further again on long-term acid-reducing medication. A plant-based diet without supplementation makes it close to inevitable.
Symptoms can include memory complaints, confusion and difficulty concentrating, alongside the more familiar fatigue and pins and needles. A serum B12 test is routine and cheap; where results sit in the grey zone, a methylmalonic acid test resolves it.
Vitamin D
Low status is widespread at northern latitudes, particularly in people who are indoors most of the day or who cover up outdoors. The association with cognitive measures is real but weaker and messier than the B12 picture, and supplementation trials have been underwhelming.
Worth testing, worth correcting if low, and worth being sceptical of anybody selling it as a memory intervention.
Folate
Interacts with B12 closely enough that they are usually tested together. Supplementing folate while a B12 deficiency goes unnoticed can mask the blood picture while neurological damage continues, which is the specific reason to test rather than to self-prescribe.
Iron
Less discussed in this context than it should be. Iron deficiency produces fatigue and difficulty concentrating well before anaemia shows up on a full blood count, and ferritin is the test that catches it earlier.
The two-week version
Ask for a panel covering B12, folate, ferritin, vitamin D and thyroid function. Bring a list of everything you currently take, prescribed or otherwise. Those two things together resolve a surprising share of memory complaints, and they resolve them properly rather than approximately.
If the panel comes back clear and the complaint is ordinary — names, appointments, the occasional lost word — then the general-support shelf is a reasonable place to look next. In that order, not the other way round.