Even though you can breathe normally, your brain may not be getting enough oxygen. Lack of oxygen in the brain is not something the average person can recognize. However it can cause poor brain function and increase the risk of vascular dementia, the second most common form of dementia after Alzheimer’s. The brain can be hungry for oxygen years or decades before dementia sets in. Risk factors include high or low blood pressure, heart disease, diabetes, smoking, alcoholism, and high cholesterol.