What is Baking Powder?
Traditional baking powder is essentially composed of a mixture of tartaric acid and bicarbonate of soda (baking soda). Although baking soda is commonly found with aluminum salts.
Baking Powder and Aluminum
The use of aluminum compounds as food additives is a source of concern, given the scientific data regarding the safety of aluminum in the diet. High levels of aluminum have been found in the brain tissue of people who suffered from neurological conditions such as Alzheimer's disease. While the use of aluminum pans for frying has become less common due to this concern, aluminum is still being added to the diet via baking powder, aluminum cookie sheets, and other conduits. 
It's recommended to use aluminum free baking soda in recipes and eat store bought food that strictly displays "Aluminum Free" on the label to avoid any health issues.