We've all had moments where we don't remember where we put our car keys, or forgot the specific thing we went to the store to buy. That's normal. What shouldn't happen is serious memory loss, including diseases like dementia and Alzheimer's.

The brain is an incredibly complex organ, so much so that a great deal of it remains a mystery. This includes many of the memory functions: while scientists have "mapped out" most of the brain's areas, there are still many unanswered questions, such as the role of sleep and dreaming in memory retention, how various areas of the brain interact, and how to tell if someone is at risk for memory loss. Still, doctors do know some of the precautions that can be taken to keep the brain healthy, including proper diet, regular sleep patterns, brain "exercises," and substances to avoid.

Memory is a very complex procedure, involving different areas of the brain. It involves both short-term memory - remembering where in the parking lot you put the car - and long-term memory, such as the name of the dog you had when you were a child. These are stored in different areas of the brain, which is why it's common for people with injuries or diseases affecting a portion of the brain to lose only one type of memory: dementia patients who don't remember their last meal, but vividly recall their wedding day forty years ago. There are also different types of information the brain remembers: an amnesia patient may not know her own name, but remembers how to tie her shoes.

It is important to combine diet and exercise, nourishing the brain, with exercises that target the memory centers, creating a "whole health" regime that can strengthen the body and possibly help avoid memory loss.

Dementia is a Latin term meaning "apart from the mind." It is a gradual and irreversible deterioration of memory skills. It can have several root causes, including stroke, cardiovascular disease, brain injury and long-term substance abuse. Alzheimer's disease is the most common cause of dementia, but it is not the only one. The earliest sign of dementia is usually forgetfulness, but as the condition progresses, it can also affect the ability to speak, walk or control bodily functions. It is possible to suffer dementia at any age, depending on the underlying cause, but it is far more common in older people. However, it is not aging itself that causes dementia, but underlying diseases that become more common as people age.

Since strokes can be a major factor in dementia, especially when Alzheimer's is already present, the root causes of stroke can also be said to affect memory, including high blood pressure, cardiovascular disease, high cholesterol levels, smoking, diabetes and overweight.

Not all memory loss is catastrophic, though, and many people experience temporary difficulties with memory, for a variety of reasons. So-called "fuzzy brain," minor difficulty with short-term memory and concentration, is common for women in menopause. Memory problems can also be linked to certain prescription medications, thyroid problems, vitamin B12 deficiency, depression, stress, lack of sleep, alcohol, "recreational" drugs, abnormally high levels of sodium or calcium, kidney or liver disease, poor diet, and head injuries such as concussion. In most cases, treating the underlying problem will also restore normal memory function.

Many of the underlying causes of memory loss, including dementia, are due to preventable diseases and conditions.

Eating fresh fruits and vegetables, limiting saturated fat, and cutting back on processed foods will help maintain cardiovascular health, which in turn will help prevent strokes that are a major factor in irreversible memory loss. There are also several nutrients that specifically help to keep the brain healthy, including antioxidants, vitamins C, E and B12, beta carotene, lecithin, folic acid, and omega-3 fatty acids.

Exercise is important: those in their 70s and 80s who are still mentally sharp are generally also physically active. Exercise increases blood flow and helps to maintain body and brain health. Likewise, that which is bad for the body is bad for the brain, such as smoking or too much alcohol. The effects of being overweight can lead to strokes, diabetes and heart disease, which will in turn affect the brain, but a recent study at Northwestern University in Chicago found evidence that excess weight in older women caused memory difficulties even though they had no other medical conditions.

Along with exercising the body, exercise the brain. Studies show that people who read books, play games, participate in social activities and perform other cognitive exercises are less likely to have memory problems than those who do not. The key is to be an active participant: memory loss is more likely among those who watch a lot of television than those who limit their hours in front of the set.

It's important to cut down on stress, which produces a hormone called cortisol, which can affect the brain's hippocampus over time, affecting memory. Sleep difficulties will also add to memory problems, and it's important to take steps to ensure a full night's sleep.