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.
With the exception of vitamin B 12 a vegan diet can in principle provide all necessary nutrients. However, in practice, vegans are frequently deficient in calcium , iron , vitamin D , selenium , phosphorous , and zinc . Vitamin B 12 presents a special issue. This vitamin is not provided to any meaningful extent by non-plant foods. (The algae spirulina contains B 12 , but in a non-absorbable form.) Deficiency in B 12 is therefore inevitable among those who follow a strict vegan diet and do not take supplements.