A concussion is a type of traumatic brain injury in which a forceful bump, blow or jolt to the head causes the brain to move inside the skull. This can result in headache, nausea, dizziness, blurred vision, and sluggishness. In some cases, there may be confusion and memory problems, as well. Symptoms typically appear within the first 7-10 days and often resolve within weeks or months but may persist for more than a year.

Concussions are surprisingly common with nearly 4-million occurring annually in the US. According to an NPR-Truven Health Analytics Poll, 1 in 4 Americans has suffered a concussion at some point in their lives and more than one-third said they had suffered 2 0r 3 concussions.

Depending on the severity of the trauma, when the brain moves inside the skull, there may be changes in brain chemistry, bruising, bleeding, and stretching of and damage to brain cells. These changes may have consequences long after the initial symptoms resolve.

A lesser-known potential result of concussion is that it is associated with a significantly increased the risk of Alzheimer’s disease and other dementias even 30 years later. It may also accelerate the age of onset for cognitive decline.

It’s not entirely clear why this relationship between head trauma and dementia exists, but there are some clues. We know head injury leads to an inflammatory response in the brain and neuroinflammation is present at all stages of Alzheimer’s disease. Brain injury can also lead to the production of unstable molecules called free radicals that can damage neurons and it may also damage tiny blood vessels and thereby reduce blood and oxygen flow in the brain. It’s also possible that brain injury causes the accumulation of abnormal proteins in the brain, as happens in Alzheimer’s disease, which subsequently cause neuron cells to die.

Much of the studies of brain injury and subsequent risk of dementia have focused on athletes and combat veterans. Former Chicago Bears quarterback Jim McMahon is the athlete who put the subject of traumatic brain injury in sports on the public map. In 2011 he shared his own struggles with dementia. Later, Mark Gastineau, who played for the New York Jets, revealed that he had received a double diagnosis of Alzheimer’s disease and Parkinson’s disease, which he attributes to his ten-season career in football. By 2014, the evidence for the risk posed to professional football players was so great that the NFL entered into a settlement with 5,000 former players who were already suffering from, or expected to suffer from, various forms of dementia as a result of their profession.

Soccer players have become equally concerned about their long-term cognitive health. The Field Study, conducted by the University of Glasgow’s Brain Injury Group, found a five-fold increased risk of Alzheimer’s disease among former professional soccer players when compared to the general public. It’s noteworthy that goalkeepers, who do not head the ball, do not share the elevated risk.

A study of 178,779 Afghanistan and Iraq war veterans found an increased risk of 2.5 times in those who experienced mild concussion without a loss of consciousness, 2.8 times if there was a loss of consciousness, and 3.8 times in severe brain injury with a loss of consciousness.

Obviously, we are wise to do everything within our power to protect ourselves while participating in activities that pose a risk for head trauma. We should wear appropriate protective headgear while skiing, cycling, horseback riding, and ice-skating, among other sports. However, as the NFL studies show, even a helmet may not be sufficient to prevent injury to the brain.

Despite the growing focus on athletics, falls remain the most common cause of concussion. To lessen the chance of falls in the house, consider installing grab bars around tubs, toilets, and inside showers. Be sure that rugs and carpeting are affixed securely to the floor using non-slip rug pads or Velcro. Avoid leaving books, magazines, or other papers on the floor. Add non-slip adhesive strips to slippery tile, outdoor and indoor steps, and hardwood floors. Instead of socks, wear a house shoe or slipper that has a rubber sole. Look for and remove tripping hazards such as extension chords or lamp cords. Finally, always wear a seat belt when driving or riding as a passenger in motor vehicle.

Because every case of head injury is potentially serious, even in the absence of symptoms, one should always be evaluated by a medical expert.