Alzheimer’s disease is a progressive neurological (brain) disease that leads to dementia, which is the loss of cognitive functions such as memory, thinking, and reasoning. It’s most common in people ages 65 or older; in fact, age is the biggest known risk factor for Alzheimer’s.1

Aging itself does not cause Alzheimer’s. Complex brain changes can begin years or even decades before you begin any symptoms. Researchers believe a combination of genetics plus lifestyle and environmental factors leads to the development of this condition.

There are two types of Alzheimer’s: early-onset and late-onset. People with late-onset disease get symptoms at ages 65 or older. It’s by far the most common type of Alzheimer’s. Less than 10% of people with Alzheimer’s have early-onset, developing symptoms between their 30s and mid-60s.

It’s still impossible to predict who will get Alzheimer’s. Researchers are actively studying risk factors and have come up with several hypotheses for what brain changes cause the disease. Here’s what they’ve proposed so far.  


Alzheimer’s results in a major loss of brain cells (neurons) and their connections (synapses), starting in the areas of the brain that control memory. As damage spreads throughout the brain, more cognitive and physical abilities are affected. This causes the brain to physically shrink.

There are two main hypotheses for the development of Alzheimer’s: cholinergic and amyloid.

Cholinergic Hypothesis

The cholinergic hypothesis is the earliest explanation of Alzheimer’s. Cholinergic neurons throughout the brain play an important role in cognition (learning and understanding). People with Alzheimer’s disease show a severe loss of cholinergic neurons and a deficiency of acetylcholine (ACh)—a brain chemical messenger that is important for learning, memory, and other functions. 

The only approved medications for Alzheimer’s help maintain the level of ACh in the brain. These drugs can temporarily slow down cognitive symptoms, but they don’t prevent long-term brain damage.

Amyloid Hypothesis

For many years, researchers believed that abnormally high levels of beta-amyloid (a protein that surrounds the nerve cells) formed amyloid plaques in the brain. It is thought that these plaques are what contribute to the cognitive loss associated with Alzheimer’s. The beta-amyloid hypothesis was based on an influential 2006 paper published in the journal Nature.   

However, medications targeting beta-amyloid did not improve Alzheimer’s symptoms. Additionally, researchers found that amyloid plaques can also be found in people without Alzheimer’s as they age.

Then, in July 2022, a Science magazine report cast doubt on this major hypothesis. One neuroscientist found that the images in the 2006 study were altered. Since then, researchers have approached the beta-amyloid hypothesis with caution. 

In November 2022, results from the clinical trial of a medication called Leqembi (lecanemab) showed some renewed support for the role of beta-amyloid in Alzheimer’s development. Lecanemab reduced the amount of amyloid in participants’ brains, resulting in a moderate improvement of symptoms after 18 months. 

More research and trials are necessary to confirm the now-debated hypothesis. Investigators are also looking into new explanations for neuron loss as well. 

Is Alzheimer’s Disease Hereditary?

Some cases of early-onset Alzheimer’s are familial, meaning children may inherit certain mutations from their parents. In those cases, gene mutations cause the disease. Consider speaking to a healthcare provider about genetic testing if you have a history of early-onset Alzheimer’s in your family.

About 70% of Alzheimer’s cases are related to genetic factors. But the genetics of late-onset Alzheimer’s is less clear: It doesn’t seem to run in families. 

The gene that can affect your risk of late-onset Alzheimer’s the most is apolipoprotein E (APOE). Everyone has some form (or variant) of APOE in their DNA. However, you’re more likely to develop the disease if you inherit the ɛ4 variant. On the other hand, having the relatively rare APOE ε2 variant can actually help protect you from Alzheimer’s.

Who Gets Alzheimer’s Disease?

Some people are more likely to develop Alzheimer’s than others. Factors that can contribute to risk include:

  • Age: This is the most important risk factor; most Alzheimer’s symptoms start after age 65, and the percentage of people who have Alzheimer’s increases with age. Forty percent of people over the age of 85 have Alzheimer’s.
  • Biological sex and gender: Nearly two-thirds of Alzheimer’s cases are in people assigned female at birth. But women may not be at an increased risk of Alzheimer’s. For example, the difference may appear because women live longer than men on average; in the United States, the rates of women and men who develop Alzheimer’s at each age are the same. Recent studies have also revealed sex and gender bias in older research. 
  • Ethnicity: Black and Hispanic populations may be at a higher risk but, as with sex and gender, newer studies have challenged this idea. When researchers consider socioeconomic factors and health conditions (such as the high rates of heart disease and diabetes in Black and Hispanic populations), the differences in risk go away. Structural racism can affect other social and environmental risk factors for Alzheimer’s as well.

Risk Factors

While the cause of Alzheimer’s disease is unknown, researchers have identified different conditions, injuries, and other circumstances that can also contribute to the development of Alzheimer’s.

Vascular (Blood Vessel) Conditions

These conditions include high blood pressure (hypertension), heart disease, and stroke. Issues with blood vessels (for example, because of heart failure) can affect the blood supply to the brain, which can lead to brain inflammation and eventually Alzheimer’s. 

Metabolic Conditions

These include type 2 diabeteshigh LDL cholesterol, and obesity. Specifically, experiencing high LDL cholesterol levels and obesity during your midlife can increase your Alzheimer’s risk.


Depression can raise your risk of Alzheimer’s. Antidepressant treatment may reduce this risk, but there aren’t enough studies to say for sure.  

Depression can also be an early sign of Alzheimer’s, as dementia can cause similar mood symptoms.

Social Isolation and Loneliness

Social isolation means lacking social interaction. Loneliness is different—it’s feeling alone or separated, which can happen even when you’re around other people. Both are risk factors for Alzheimer’s disease. 

Fortunately, getting back into social activities can help protect you. You can improve your mood, cognition, and overall well-being by talking to others or volunteering.

Traumatic Brain Injury (TBI)

Traumatic brain injury happens when you experience a blow or jolt to the head. A history of TBIs (for example, in people who play sports) can increase the risk of Alzheimer’s. This is especially true for severe injuries, but even mild TBI (like a concussion) can have a long-term impact.

Heavy Alcohol Use

Heavy alcohol use is associated with changes in the brain and cognitive decline, though there’s not enough evidence to say that it causes these issues. This doesn’t mean you have to quit alcohol entirely—light to moderate drinking in middle to late adulthood has been shown to decrease the risk of cognitive decline and dementia.


People who’ve never smoked or have quit smoking long-term may have a lower risk of developing Alzheimer’s. If you don’t stop smoking completely, decreasing the habit can still reduce your risk. 

Secondhand smoke can also increase your chance of developing Alzheimer’s—especially if you’re exposed at home.

Hearing Loss

Alzheimer’s is associated with hearing loss, but researchers don’t know why, or if one condition causes the other. A major hypothesis is that hearing impairment may lead to social isolation, which is a risk factor for Alzheimer’s. Another hypothesis is that people with hearing loss require more cognitive resources in order to process sounds, which leaves fewer resources for other cognitive functions.

Air Pollution

Higher levels of tiny particulate matter are associated with higher rates of Alzheimer’s. This matter (PM 2.5) is pollution from sources like power plants, construction sites, and fires. 

Other types of pollution, such as nitrogen oxides (emitted from burning fuel in cars and power plants) and sulfur dioxide (emitted from burning fossil fuels at industrial facilities), can also cause brain damage similar to that seen in people with Alzheimer’s.

Physical Inactivity

Being active reduces your risk of Alzheimer’s (and all other causes of dementia). One 2022 review considered studies that followed participants for at least 20 years and found that physical activity could help protect against Alzheimer’s long-term.

Low Mental Engagement

Just like physical activity is important, staying mentally active—especially before age 20—can help protect you from Alzheimer’s. Studies have shown that higher education can reduce your risk of dementia, but so can other cognitively stimulating activities like reading, speaking a second language, and playing music. Having a mentally challenging job can also help.

A Quick Review

Alzheimer’s results in the loss of cognitive functions like memory and thinking, typically in people aged 65 or older. Researchers don’t yet know how Alzheimer’s develops, though it’s likely because of a combination of genetic and environmental factors. 

Age is the biggest risk factor for Alzheimer’s. Other known risks include heart disease, brain injury, and low mental or physical activity. New studies are including demographically diverse populations to better understand who gets Alzheimer’s, but there’s no way to predict exactly who will develop it at this time.

It can be scary to live with a disease that doesn’t have a known cause but remember: Alzheimer’s research is always ongoing. A healthcare provider can help explain what to expect if you or a loved one are diagnosed.


  • A new study tracked rates of BMI obesity for 20 years and found that many obese people were actually metabolically healthy.
  • BMI has been noted as an inherently flawed health metric, but is still widely used in the medical community as a quick, easy means of assessing an individual’s health status.
  • Experts recommend doctors analyze health from a more well-rounded perspective, including BMI, body composition, and metabolic health.

A person’s body mass index (BMI) is often used as an indicator of their general health, but that’s not always the most accurate tool, a new study found.

The JAMA study, published March 9, tracked rates of BMI obesity from 1999 to 2018, and found that many obese people with elevated BMIs were actually metabolically healthy, meaning they didn’t have elevated blood pressure, blood sugar, bad cholesterol, or triglyceride levels.1

The general prevalence of people with metabolically-healthy obesity (MHO) increased from 3% to 7% during the 20-year period. Individuals with MHO now make up a larger proportion of those with obesity; though the percentage of MHO increased, the levels of metabolically-unhealthy obesity and general levels of obesity also went up.1

“We define obesity based on BMI, and that inherently is flawed,” Mohini Aras, MD, obesity medicine specialist at the comprehensive weight control center at Weill Cornell Medicine and who was not involved in the study, told Health. “People with the same BMI can have markedly different weight-related medical comorbidities and health risks.”

BMI and Metabolic Health

Researchers looked at ten cycles of National Health and Nutrition Examination Survey (NHANES) data from 20,430 participants between 1999-2000 and 2017-2018.

Researchers looked at 7,386 participants with obesity, or a BMI over 30, and assessed their metabolic health. Over the 20-year period, the study found that BMI obesity rates increased from 28.6% to 40.9%. The number of those with metabolically-unhealthy obesity also jumped during this period, from 25.4% to 34.3%.

Both these categories also increased within the general population during this timeframe.

“The prevalence of [MHO] has increased among obese people. The new news is that we’re more obese—there are more people who are metabolically unhealthy obese, and there are more people who are [MHO] in the last 20 years,” Sam Klein, MD, director of the Center for Human Nutrition and of the weight management program at the Washington University School of Medicine in St. Louis, told Health. He was not involved in the study.

Interestingly, while metabolically-unhealthy obesity and general obesity saw a more steady rise, MHO jumped sharply between 1999 and 2006, but has only increased marginally since then. Experts aren’t quite sure why.

Body Mass Index (BMI) is a dated health measure that does not account for several factors, like body composition, ethnicity, race, gender, and age.

This said, BMI is still used in the medical community as an inexpensive and quick method for analyzing potential health status and outcomes.

Of the four metrics used to determine metabolic health—elevated blood pressure, cholesterol, blood sugar, and levels of triglycerides (a type of fat) in the blood—only two decreased during the survey period. In the late 1990s and early 2000s, many people were concerned with cutting out fat from their diets and many were treated aggressively for high cholesterol and triglycerides, Dr. Aras explained. This could explain why MHO increased so quickly from 1999 to 2006, she posited.

While positive changes in public health patterns have occurred, the incidence of high blood pressure has stayed stagnant and the percentage of high blood glucose levels has increased substantially among the BMI-obese population since 1999.

Researchers also found that men, older people, white people, those with a higher income, those with a BMI closer to 30, and those with private insurance saw larger MHO increases.

Though the mechanisms behind the MHO’s rise is unclear, Dr. Klein said, we do know that all kinds of BMI obesity have increased in the U.S. between 1999 and 2018, even though BMI at face value doesn’t tell us the whole story about the health of that population.

The Problem with Tracking Weight and Health

In addition to its findings on obesity rates, the study also illuminates some of the challenges that come with trying to measure weight and health. Every person’s experience with weight is different, Dr. Aras noted, so making broad conclusions about an entire population can be challenging.

“We don’t know the whole story just based off of BMI,” Vijaya Surampudi, MD, assistant professor of medicine at the Center for Human Nutrition at UCLA Health, told Health.

BMI is based on a person’s weight and height, which can sometimes indicate whether they’re at a healthy weight. But that’s certainly not always the case.

“You just have a weight and the height, but it doesn’t give you any information of how weight is deposited on the body,” observed Dr. Surampudi, who was not involved in the study.

A BMI over 30 is considered obese. Using this metric, somebody tall and muscular—like Dwayne “The Rock” Johnson, Dr. Klein said—would be considered obese. This is obviously uncommon, but still illustrates some of the errors inherent in the tool.

BMI aside, judging whether a person is healthy is challenging. The four criteria that these researchers used to determine a metabolically-healthy person are not universally agreed upon, which means that these definitions of health can vary from person to person.

“There [are] no standardized definitions for [MHO],” Dr. Klein clarified. “Depending on the definition that’s used, depending on the population being studied, you can get a large variability in the prevalence of [MHO] in different studies.”

Despite the challenges of judging weight at a public health level, looking at body composition can be a useful tool when determining an individual’s health, Dr. Surampudi explained. This allows doctors to look at the amount of muscle and different types of fat in the body, giving a much clearer picture of overall health.

More to Learn About People’s Experiences with Weight

Though the disconnect between metabolic health and BMI is clear, more work needs to be done to figure out why some people with obesity are healthier than others, noted Dr. Klein.

Men, white people, older people, and privately insured people saw more increases in MHO. This could suggest that MHO is a consequence of better medical advice and having more time to exercise and eat well, Dr. Aras reasoned.

The type of obesity a person has seems to have something to do with the different types of fat in their body—whether they have more fat around the organs, or in other places, such as under the skin. Though Dr. Klein noted it’s also unclear if those differences cause better or worse metabolic health, or if they’re yet another effect of something else.

“If we can understand what protects [people with MHO] from the adverse effects of excess body fat, and what predisposes other people to adverse metabolic effects of excess body fat, we would go a long way into developing better treatments to improve the health of people with obesity, without even changing their body weight,” explained Dr. Klein.

Another large factor at play is doctors’ ability to determine whether someone has MHO or metabolically-unhealthy obesity. For example, people with MHO could be told to lose weight when in actuality, Dr. Klein said, it would do little to improve their health.

While BMI isn’t always an indicator of health, obesity can affect some people’s ability to move and breathe well and can put them at risk of other diseases, such as type 2 diabetes. Since consequences of weight is different for each person, Dr. Aras recommended those with higher BMIs be evaluated to see what effect, if any, their weight is having on their health.

“Diet and activity are the foundation of this,” she said. “It’s not necessarily the number on the scale.”


Image by David Illini / Stocksy

When you come across a statistic stating that early-onset dementia diagnoses are up 200%, it’s only normal to wonder what you can do to protect yourself.  

We’ve long known that dementia is partially connected to lifestyle factors. In fact, Alzheimer’s disease has been referred to as “type 3 diabetes,” and now a new study suggests that one diet may particularly help lower dementia risk.

Can the Mediterranean diet lower dementia risk?

Performed by researchers at Newcastle University in England, the study involved collecting data from more than 60,000 participants for over 10 years. The participants were assessed for genetic risk factors for dementia, and they also completed a dietary assessment that allowed the researchers to score them based on how much their diet consisted of foods in the Mediterranean diet plan. 

The results showed that after 10 years, 882 participants developed dementia. When the researchers looked to see whether the patients’ diets were associated with a higher or lower risk of developing dementia, they found that those eating a Mediterranean diet (or the closest to it!) had a significantly lower risk.

But how much, exactly? The results showed that those on a Mediterranean-like diet had up to a 23% lower risk of developing dementia compared with those not on the diet. 

Is a Mediterranean diet the best diet for dementia? 

What’s more, the Mediterranean diet affected participants who had genetic risk factors for dementia just as much as it affected those who didn’t have those genetic risk factors, meaning nutrition is a powerful tool even if you’re at a higher risk of the illness.

John Mathers, Ph.D., study author and Professor of Human Nutrition at Newcastle, noted in a statement, “The good news from this study is that, even for those with higher genetic risk, having a better diet reduced the likelihood of developing dementia.”

This study doesn’t tell us that a Mediterranean diet can prevent dementia, nor does it tell us whether it’s the best diet for reducing our risk. But it is a step in that direction, as it’s the first large study showing a link between this eating pattern and a lower risk of dementia. Past studies have been too small to draw any firm conclusions. Mathers continued, “Although more research is needed in this area, this strengthens the public health message that we can all help to reduce our risk of dementia by eating a more Mediterranean-like diet.”

How to lower your dementia risk today.

We can’t draw any hard and fast conclusions from this study, but it sure looks like a Mediterranean diet is a healthy brain diet. Not to mention its other benefits, like improved cardiovascular health, increased longevity, and weight loss. So, how can we make our diet more Mediterranean-like? 

Eat more fish: Fish is a staple of the Mediterranean diet, which contains high levels of healthy anti-inflammatory fats. Reach for omega-3-rich options like salmon, herring, or sardines. Not that into fish? Try supplementing with an omega-3 supplement instead.

Eat a diverse range of fruits and vegetables: One of the major characteristics of the Mediterranean diet is a colorful plate of fruits and veggies. This helps provide your gut microbes with a diverse range of food and gives you a dose of antioxidants.

Avoid processed foods: A Mediterranean diet comprises whole foods. It doesn’t involve many packaged or processed foods (think a long lazy lunch versus a grab-and-go meal). Try to avoid highly processed foods, which often contain added sugars, refined grains, trans fats, and refined vegetable oils (soybean oilcorn oil, etc.)

The takeaway.

A new study—the largest of its kind—shows that following a Mediterranean diet is correlated with a lower risk of developing dementia. The good news is that you can start adopting a more Mediterranean way of eating today! 


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