Age

Alzheimer’s disease is the most common form of dementia. About a third of people 85 and older show signs of the disease. The genes you get from your parents play a part at this age, but so do things like diet, exercise, your social life, and other illnesses. Dementia is not a normal part of getting older.

Heart Disease

It could lead to a heart attack or stroke, which makes dementia more likely. Heart disease is usually caused by plaque buildup in arteries around your heart (atherosclerosis). That can slow blood flow to your brain and put you at risk for stroke, making it harder to think well or remember things. And many things that cause heart disease -- tobacco use, diabetes, high blood pressure, and high cholesterol -- also can lead to dementia.

Diabetes

Doctors are not sure exactly why people with diabetes get dementia more often. But they do know that people with diabetes are more likely to have damaged blood vessels. This can slow or block blood flow to the brain, and damage areas of the brain, leading to what is called vascular dementia. Some people may be able to slow brain decline if they keep diabetes under control with medicine, exercise, and a healthy diet.

High Cholesterol

High cholesterol levels, especially in middle age, are linked to obesity, high blood pressure, and diabetes. All of these boost your risk of dementia, but it is not yet clear if cholesterol by itself adds to the problem. Some research shows that high cholesterol in midlife could be a risk for Alzheimer’s disease later in life, but the exact link is not clear.

High Blood Pressure

Even if you had no other health problems, having high blood pressure makes you more likely to get vascular dementia and Alzheimer’s. That is probably because high blood pressure harms the blood vessels in your brain. It also can lead to other conditions that cause dementia, like stroke. Managing your blood pressure with diet, exercise, and medication, if needed, may slow or prevent this from happening.

Depression

If you have ever had this common condition, you may be more likely to get dementia. Scientists are not yet sure that it is a cause. It may simply be an early symptom or a sign of other causes like Parkinson’s and Huntington’s diseases. Talk to your doctor or a therapist if you feel down for more than 2 weeks, and right away if you think of harming yourself. Therapy and medication can help treat depression.

Head Injury

One mild traumatic brain injury may not make you more likely to get dementia later in life. But more severe or repeated hits or falls could double or quadruple your chances, even years after the first time. Get to the hospital if you have hit your head and you faint or have blurry vision, or feel dizzy, confused, nauseated, or become over-sensitive to light.

Obesity

Having a lot of extra weight in middle age could put you at risk. It also drives up your odds of getting heart disease and diabetes, which are linked to dementia. You can check your BMI (body mass index) online to see if it is in the “obese” range. Your doctor can help you set a weight loss goal that is right for you. A healthy diet and regular exercise could help you turn things around.

Genes

They seem to matter more in some types of dementia than others. But dementia does not always run in families. And even risky genes do not mean you will get it. If you are thinking about genetic testing for Alzheimer's, ask your doctor about the pros and cons -- and about genetic counseling. Doctors do not routinely recommend those tests.

Stroke

The most common kind blocks the flow of blood to areas of the brain. Afterward, damaged blood vessels can make it hard to think, speak, remember, or pay attention (vascular dementia). Things that make a stroke more likely -- like high blood pressure, heart disease, and smoking -- also raise your risk of this type of dementia. Think “FAST” for stroke symptoms: Face drooping, Arm weakness, Speech problems? Time to call emergency.

Poor Sleep

Many people have a bad night of sleep now and then. But if it happens often -- you wake up a lot or do not sleep enough -- you could be more likely to get dementia, including Alzheimer’s disease. Set and stick to a smart sleep routine: Avoid alcohol, caffeine, and electronics in evening, and set up a soothing bedtime ritual with regular bedtime hours.

Smoking

It is bad for your blood vessels, and it makes you more likely to have a stroke, which can cause vascular dementia. That might lead to problems with thinking or remembering. Talk to your doctor or a mental health professional if you smoke and want support to quit.

Dementia With Lewy Bodies

In this and other forms of dementia, proteins called Lewy bodies build up and damage brain cells. Dementia with Lewy bodies can lead to problems with memory and movement. Someone with this condition might act out dreams or see things that are not there (hallucinations). Although there is no cure, your doctor can help treat symptoms.

What Helps: Diet

Talk about a win-win. The traditional Mediterranean-style diet that is so good for your heart is also good for your brain. It features whole grains, fruits, vegetables, fish, nuts, olive oil and other healthy fats like avocado (in moderation), and keeps red meat to a minimum.

What Helps: Exercise

People who are physically active are more likely to stay mentally sharp and less likely to get Alzheimer’s and other types of dementia. If you already have early stages of these conditions, being active may help you think more clearly and remember things. You do not have to go to extremes. Just get out for some brisk walking, dancing, gardening, or something similar. Build up to 30 minutes or more on most days of the week.