I had dementia symptoms with B12 malabsorption. In my case due to autoimmune pernicious anaemia. I had severe B12 deficiency. It took a month for my memory to start improving after weekly B12 injections. I switched to 2000 mcg daily of sublingual (under the tongue) B12 spray which I find superior personally. I have permanent nerve damage.
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Excerpt from Livestrong - Be Aware of Alcohol's Effects on B-12 Absorption..
“Most people enjoy drinking alcohol, but even moderate amounts of alcohol consumption can have negative effects on the amount of vitamin B-12 you absorb.
Moderate-to-severe chronic alcohol consumption can have damaging effects on your stomach lining, causing a condition called atrophic gastritis, or inflammation of the stomach. When this occurs, the cells of the stomach cannot do their job of making and secreting a substance called intrinsic factor, which enhances B-12's absorption.
When intrinsic factor is negatively affect by alcohol, your body will not be able to absorb sufficient amounts of this nutrient, leading to vitamin B-12 deficiency.
Without intrinsic factor or a diet that contains the recommended intake of vitamin B-12, the amount of vitamin B-12 found in the body is decreased. When this occurs, these signs and symptoms of a vitamin B-12 deficiency occur: fatigue, shortness of breath, tingling and numbness in the extremities, headache, dementia, disorientation, and loss of concentration and memory.
In severe cases, a vitamin B-12 deficiency by permanently damage your nerves, leading to lifelong side effects.“