Parkinson's disease (PD) is a type of movement disorder. It happens when nerve cells in the brain don't produce enough of a brain chemical called dopamine. Sometimes it is genetic, but most cases do not seem to run in families. Exposure to chemicals in the environment might play a role.
Why Vegans are Often Deficient in Vitamin B12. The few plant foods that are sources of B12 are actually B12 analogs. An analog is a substance that blocks the uptake of true B12, so your body's need for the nutrient actually increases.
A vegan diet does not include any animal-derived products, such as meat, fish, milk, eggs, butter or cheese. It does include non-animal products such as vegetables and fruits (including potatoes), grains (bread, rice, oatmeal, etc.), beans (including lentils), nuts etc.