- Currently, neurodegenerative conditions, such as Parkinson’s and Alzheimer’s diseases, are challenging to preempt.
- A large-scale, innovative new study investigates how hormonal, dietary, metabolic, and digestive issues may help predict these conditions years before they begin.
- The study identifies several conditions that are associated with an increased risk of Alzheimer’s and Parkinson’s.
- Importantly, the findings also hint at ways to help reduce the risk of developing these disorders.
A new study, published in Science Advances, investigates links between 155 health conditions and the future risk of developing Alzheimer’s and Parkinson’s.
The scientists identified several relatively easy-to-treat conditions that are linked to the later development of neurodegenerative conditions, years before symptoms begin.
Additionally, the study identifies that the timing of each condition affects the size of the risk increase.
There are many versions of neurodegenerative diseases — conditions marked by the degradation of the brain — but Parkinson’s and Alzheimer’s are the most common.
Despite decades of focus and millions of dollars worth of research, they remain steadfastly difficult to predict and treat.
Once these conditions begin, some drugs can slow progress for some patients; however, there is no cure, and no surefire way to know who will develop them.
Medical News Today spoke with Lucy McCann, MBChB, MSc, ANutr, a medical doctor and registered nutritonist, about the importance of this study.
“Alzheimer’s and Parkinson’s disease are among the most common neurodegenerative disorders in the world. With an aging population, preventing and managing these conditions is becoming a public health priority,” McCann, who was not involved in the research, explained.
Research has also shown that the processes involved in these diseases begin decades before symptoms appear. Because of this, scientists are focusing on identifying any clues from middle age that could provide opportunities to stop disease progression in its tracks.
In recent years, scientists have focused on the potential role of the so-called gut-brain axis in neurodegenerative diseases. In short, the gut-brain axis is two-way communication between the gut and the brain.
The communication has many modalities, including:
- hormonal, for example through gut peptides
- nervous, e.g. the vagus nerve
- immune, e.g. cytokines.
These messaging pathways and more, as the authors of the new study explain, facilitate “constant interactions between the brain, digestive, endocrine, metabolic systems and nutritional status.”
The nervous system of the gut, known as the enteric nervous system, is the second largest collection of neurons outside of the brain.
At first glance, it is difficult to understand why the brain and gut are so intimately linked. However, when we remember that food is essential for our survival, and that we cannot find it without our brain, the connections begin to make sense.
When the gut-brain axis is disrupted, it can cause all manner of issues, including gut pain, mood disturbances, and irritable bowel syndrome (IBS).
Importantly for this study, these disruptions may also influence an individual’s risk of developing Alzheimer’s disease or
Alongside conditions involving the gut-brain axis, scientists have also identified links between hormonal and metabolic conditions and an individual’s risk of developing a neurodegenerative condition.
For instance, the authors of the recent study explain that more severe cases of diabetes and imbalances in thyroid hormones — both hypo- and hyperthyroidism — are associated with Parkinson’s disease. Similarly, type 2 diabetes is a well-known risk factor for Alzheimer’s disease.
Because of these links, researchers are investigating antidiabetic drugs as a potential treatment for both of these neurodegenerative conditions.
At the same time, some nutrient deficiencies seem to play a part, including
While these findings offer some insight, many questions remain. The latest study sets out to bring some more clarity to these varied and overlapping associations.
In the latest study, the scientists investigated associations between Parkinson’s, Alzheimer’s, and 155 disorders associated with:
- the endocrine system
- nutritional factors
- the metabolic system
- the digestive system.
Interestingly, the scientists designed their analysis to examine how the timing of these conditions influenced future risk by stratifying the data into:
- 1–5 years
- 5–10 years
- and 10–15 years before an Alzheimer’s or Parkinson’s diagnosis.
The researchers found that 14 diagnoses were associated with an increased risk of Alzheimer’s disease, including:
- amyloidosis — conditions characterized by a buildup of abnormal proteins
- disorders of lipoprotein metabolism and other lipidemias — conditions marked by abnormal levels of fats, such as high triglycerides, in the blood
- gastritis and duodenitis — inflammation of the stomach or the first section of the intestines
- diabetes, both type 1 and type 2
- esophagitis — inflammation of the esophagus
- bacterial intestinal infections
- disorders of fluid, electrolyte, and acid-base balance — these include hyponatremia (low sodium), hypokalemia (low potassium), hyperkalemia (high potassium), and acidosis or alkalosis (abnormal blood pH)
- functional intestinal disorders — these are gut conditions that do not have a clear cause, such as IBS
- noninfective gastroenteritis and colitis — inflammation of the stomach and small intestine or colon that is not caused by bacteria or other pathogens
- vitamin D deficiency.
Conditions significantly associated with a later diagnosis of Parkinson’s disease included:
- dyspepsia — chronic indigestion
- diabetes, both type 1 and type 2
- other disorders of pancreatic internal secretion — these disorders include diabetes, but also hypoglycemia (low blood sugar) and increased glucagon secretion
- functional intestinal disorders
- deficiency of B vitamins.
MNT spoke to David Perlmutter, MD, a board-certified neurologist and Fellow of the American College of Nutrition, about the study findings.
“The most striking aspect is how clearly the study links systemic disorders, particularly those tied to the gut-brain axis, with neurodegeneration risk years before diagnosis,” said Perlmutter, who was not involved in this study.
“This reinforces the view that Alzheimer’s and Parkinson’s are not isolated brain diseases but the end stage of a decades-long, body-wide process,” he suggested.
The study authors investigated how the timing of these conditions influenced future risk of developing a neurodegenerative condition.
For instance, the link between type 2 diabetes and Alzheimer’s was strongest when diagnosed 10–15 years earlier compared with later diagnosis. This, the researchers suggest, may be due to “cumulative metabolic effects.”
By contrasy, a type 1 diabetes diagnosis increased the risk of Alzheimer’s to a similar extent across all three time windows.
For Parkinson’s, type 1 diabetes was most strongly associated when diagnosed 5 to 10 years before the onset of Parkinson’s, whereas type 2 diabetes had a similar risk across all three time windows.
In general, when looking at all conditions together, the links with neurodegenerative conditions were strongest when diagnosed 10–15 years earlier.
The authors wrote that “[t]hese findings underscore the importance of diagnosis timing in neurodegenerative risk modeling and suggest that both early-life exposures and recent comorbidities contribute to disease vulnerability.”
This study confirms associations between Health conditions and the risk of developing Alzheimer’s and Parkinson’s. It also adds extra depth to our understanding.
The authors hope that by drilling down into these links, doctors may be able to focus on treatments and potentially reduce or even prevent the onset of these challenging-to-manage neurodegenerative conditions.
We asked Perlmutter how the results might help reshape prevention strategies. He explained that it will put a “much greater emphasis on maintaining metabolic, endocrine, and gut health as a means of protecting the brain.”
He also told us that:
“Rather than waiting for symptoms to emerge, clinicians and individuals could use systemic health markers, such as thyroid status, blood sugar control, vitamin levels, and digestive health, as early warning signs of elevated risk.”
“What’s clear from studies like this,” McCann also explained, “is that it’s not just genes that dictate our brain health — other factors such as nutrition, metabolism, and the gut-brain connection play a crucial role.”
“Combining these features could help us predict and spot conditions such as Alzheimer’s and Parkinson’s earlier than ever before,” she added.
As is often the case with scientific research, this recent study also leaves some unanswered questions.
For instance, “It is not yet clear whether gut and metabolic disorders directly cause neurodegeneration or whether they reflect shared underlying processes such as mitochondrial dysfunction and chronic inflammation,” Perlmutter told MNT.
“These mechanisms are central to the shift of microglial cells to a pro-inflammatory state, which is an emerging mechanism in neurodegenerative conditions,” he noted.
