Is Alzheimer’s disease contagious?

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AD is a neurodegenerative disease and is not contagious. It is not possible to catch AD from another person.

Researchers are currently looking into whether it is possible to pass on amyloid proteins, a key feature of AD, through medical procedures.

According to a 2019 review, AD may share some similar features with prion diseases, such as Creutzfeldt-Jakob disease (CJD).

Prion diseases are transmissible and may pass on from person to person through invasive medical procedures.

CJD can pass on through prion proteins in blood transfusions or meat products.

Prions are proteins that can cause protein misfolding. Protein folding is how proteins form their 3D structure. Protein misfolding diseases, such as AD and CJD, occur when proteins fold in an abnormal way.

Both AD and prion diseases share some similarities, such as protein misfolding. These similarities have led researchers to question whether AD could pass on from person to person.

Research in humans found that treatment for CJD involving a human growth hormone from cadavers led to the development of amyloid proteins. There is no evidence to show that these people developed AD, however.

This procedure is no longer in use, and doctors use a synthetic growth hormone instead. The growth hormone itself does not cause a buildup of amyloid.

The review also found that transferring the brain tissue of a person with AD into mice might lead to a buildup of amyloid. Studies in mice may differ from results in human studies, though.

There is currently no evidence to suggest AD can pass on through blood transfusions or surgical equipment.

The 2019 study looked into whether AD can pass on between humans. A key feature of AD is a buildup of beta-amyloid and tau proteins in the brain.

Previous research found that beta-amyloid proteins were present in a person who had developed CJD through childhood treatment with human growth hormone containing prions and beta-amyloid. These findings suggest beta-amyloid proteins may be transmissible.

Researchers found that injecting the human growth factor with beta-amyloid and prions into mice accelerated a buildup of amyloid plaques, including in blood vessels of the brain.

Researchers also injected brain tissue from humans with AD into mice and found it led to a buildup of amyloid in blood vessels of the brain. They also found through mice studies that amyloid in the blood might travel to the brain and cause features of AD.

Other research looked at adolescents who had treatment with hormone growth factor from a cadaver to treat short stature and later developed CJD from the treatment. Researchers found that beta-amyloid and tau proteins were present in most of the vials of the human growth factor.

Although the human growth factor also contained tau proteins, there was no buildup of tau proteins in the study participants. It is not clear whether tau proteins are transmissible, or whether transmission may take longer to appear in test results.

None of the people who developed CJD via medical treatment with human growth factor developed AD. It is unknown whether they would have developed symptoms of AD if they had lived longer.

Prion diseases can spread through nonsterile surgical equipment and blood transfusions, so researchers are looking into whether this could also be true for AD.

A review of 1,465,845 people looked at whether neurodegenerative disorders could pass on through blood transfusions from donors who later developed these disorders.

There was no evidence of any increased risk of AD from blood transfusions. There is also no evidence that AD can pass on through surgical equipment.

The review concluded that amyloid may be transmissible between people in a similar way to prions, but researchers require further studies on whether this could lead to AD.

Certain lifestyle and dietary factors may help to reduce the risk of AD, including:

• preventing or controlling high blood pressure
• managing blood sugar
• maintaining a healthy weight through healthy eating and regular exercise
• staying physically active
• avoiding or quitting smoking
• avoiding excessive alcohol consumption
• getting enough quality sleep
• preventing or correcting hearing loss

Learn more about Alzheimer’s prevention and tips here.

This section answers some common questions about AD and whether or not it is contagious.

Who is most likely to inherit Alzheimer’s?

People may be more likely to inherit AD if they have a parent or sibling with the disease.

The risk of inheriting AD increases if people have more than one family member with the condition. Risk factors for AD running in families may include genetic and environmental factors.

What causes Alzheimer’s to spread?

An abnormal buildup of beta-amyloid and tau proteins plays a key role in the development of AD.

Abnormal tau proteins may gather in certain areas of the brain that affect memory. Beta-amyloid collects as plaque between neurons.

As the buildup of beta-amyloid increases, it reaches a certain level that results in a rapid spread of tau in the brain.

Over time, injury and death to neurons in the brain lead to neuron connections breaking down, and areas of the brain may shrink. In the advanced stages of AD, this damage is widespread across the brain.

Learn more

Learn more about Alzheimer’s and tau proteins.

• Alzheimer’s: How does tau disrupt brain cells?
• Alzheimer’s: How do tau tangles grow?
• Inflammation drives tau damage in Alzheimer’s

Research suggests AD may share some similarities with prion diseases, which are transmissible through invasive medical procedures.

It may be possible for amyloid proteins to transfer from person to person, although much of the research focuses on medical procedures that are no longer in use or studies in mice.

Researchers need further human studies to find out if amyloid proteins can transfer between people through medical procedures.