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.
Vegetarians have to be careful to include the following key nutrients that may be lacking in a vegetarian diet: 1  iron. 2  calcium. 3  protein. 4  vitamin D. 5  vitamin B12. 6  zinc.