Thiamine (Vitamin B1) Deficiency

Thiamine deficiency is uncommon, but it deserves attention out of proportion to how often it happens, for two reasons: it is entirely a disease of diet, and it is one of the very few causes of severe neurological illness in a cat that can be reversed within days.

Vitamin B1 is central to the way cells generate energy from glucose. Nervous tissue is particularly dependent on it, because the brain runs almost exclusively on glucose and has very little metabolic flexibility when that pathway falters. Cats also have a comparatively high thiamine requirement and store very little of it, so unlike some deficiencies that take months or years to declare themselves, this one can develop in a matter of weeks.

The classic route is a diet built on raw fish. A number of fish species contain thiaminase, an enzyme that cleaves thiamine and renders it useless, and a cat fed largely on raw fish is effectively having its vitamin destroyed in the bowl. Cooking inactivates the enzyme, which is why an occasional piece of cooked white fish is harmless while a raw-fish diet is not. Heat cuts both ways, though: thiamine itself is fragile, and home-cooked diets prepared at high temperature or reheated repeatedly can lose much of their content. Other routes include home-prepared or raw diets that were never formulated for feline requirements, prolonged anorexia, and severe gastrointestinal disease. Commercial foods are supplemented as standard, though manufacturing failures have caused recalls, which is a reminder to take notice if several cats in a household become unwell at once.

The clinical progression is fairly consistent. It starts vaguely — a cat that goes off its food, seems flat, perhaps vomits — and then becomes unmistakably neurological. The cat walks unsteadily, the pupils dilate, vision seems impaired, and the head is held with the neck bent down towards the chest, a posture called ventroflexion. Left untreated it progresses to circling, tremors, seizures, and eventually collapse. Because that same ventroflexed posture also appears with low blood potassium, and because circling and seizures have many possible causes, a vet will need the history — and your cat's diet is the piece of information most likely to point at the answer.

What makes this condition memorable is the treatment response. Thiamine given by injection to a cat in the earlier stages can produce visible improvement in hours, and substantial recovery within a day or two. Cats already seizing or comatose do less well and may be left with lasting deficits, but even then treatment is worth attempting. The practical conclusion is the same one that runs through most feline nutrition: a complete, properly formulated cat food removes the risk almost entirely, and anything home-prepared needs a nutritionist rather than a recipe blog behind it.