1. Sleep Apnea
This common but treatable sleep disorder causes breathing to stop briefly and frequently throughout the night. It is linked to memory loss and dementia, according to Constantine Lyketsos, MD, director of the Memory and Alzheimer's Treatment Center at Johns Hopkins Medicine and professor and chair of psychiatry at Johns Hopkins Bayview. You might have sleep apnea if you wake up with a headache and have daytime fatigue — or if your partner complains of loud snoring.

When not treated, sleep apnea affects spatial navigational memory, found a study published in The Journal of Neuroscience. This type of memory includes being able to remember directions or where you put things like your keys. The research suggests that deep sleep, also known as rapid eye movement (REM) sleep, plays an important role in memory.

One explanation is that for people with sleep apnea, oxygen delivery to the brain is interrupted several hundred times during the night, explains Dr. Lyketsos. “The brain is stressed, so people wake up,” he says. The injury sleep apnea causes can show up as a variety of memory loss symptoms, he adds.

2. Silent Stroke
Obvious changes in the ability to think and move normally can come from strokes that block major brain blood vessels, Gale says. Mild memory problems can also develop gradually after silent strokes that affect smaller blood vessels. These changes in brain function, which can range from mild to severe, are called vascular cognitive impairment.

The brain is especially vulnerable to blocked or reduced blood flow depriving it of oxygen and essential nutrients. People with memory loss are at greater risk for stroke. And forgetfulness may be an early warning sign of stroke, found a study published in the journal Stroke.

3. Medications
Memory loss could be a sign that your medication needs to be adjusted. Several types of drugs can affect memory, according to the U.S. Food and Drug Administration (FDA), including:

sleeping pills
antihistamines
anti-anxiety medications
antidepressants
certain painkillers
cholesterol-lowering medication
diabetes medication
The FDA also cautions that cholesterol-lowering drugs known as statins could slightly increase the risk for reversible cognitive side effects. These include memory loss and confusion.

A commonly prescribed type 2 diabetes drug, metformin, has also been associated with memory problems. A study published in Diabetes Care found that people with diabetes who took the drug had worse cognitive performance than those who did not take it.

4. Nutritional Deficiency
A lack of sufficient B12, one of the B vitamins essential for normal nerve function, can lead to confusion and even dementia. Each day, you should get about 2.4 micrograms of B12 in your diet from natural sources like dairy products, meat, and fish, or from foods fortified with vitamin B12 — like fortified cereals.

Try our free online tool to plan healthy meals that will give you the vitamins you need.

RELATED: How to Navigate the Heart-Mind Connection

5. Stress, Anxiety, and Depression
Significant stress or anxiety can lead to problems with attention and memory, cautions Lyketsos. This is particularly common among people who may be juggling home and work responsibilities and are not sleeping well. Usually, easing stress can improve memory, Lyketsos says.

Untreated chronic stress can lead to depression, which could also affect brain function, according to research published in the Journal of Pharmacy & BioAllied Sciences. A mood disorder may improve with medication and counseling, notes the National Institute on Aging.

Less Common Causes of Memory Loss
Other conditions that can lead to problems with memory include:

Infection: Memory loss may be attributed to severe infection around the brain, including neurosyphilis, Gale says.
Head injury: Symptoms of a mild brain injury may include confusion and trouble with memory and concentration, according to the U.S. National Institute of Neurological Disorders and Stroke.
Tumors: Memory and the ability to process information may be affected by brain tumors, the American Brain Tumor Association says. In addition, treatments for a tumor can affect your memory, including brain surgery, chemo, or radiation therapy.
Alcoholism, Substance Abuse: Both alcoholism and drug abuse can affect memory, says Lyketsos. A study published in Neurology found that men who drank heavily showed signs of mental decline one to six years earlier than light drinkers.