How health in midlife influences dementia risk

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A new study looks at the role of multimorbidity in dementia risk. Michael Hall/Getty Images
  • Life expectancy is increasing in many parts of the world.
  • Longer lives are playing a part in the increased prevalence of dementia.
  • Researchers are keen to understand what factors in earlier life might predict dementia.
  • In a recent study, scientists identified links between dementia and multiple chronic conditions in midlife.

In a new study, researchers found a link between increased risk of dementia and multiple chronic conditions during midlife.

The paper, which appears in the BMJ, provides scientists with information that might help people reduce their risk of dementia in later life.

According to the Centers for Disease Control and Prevention (CDC), dementias are a range of illnesses that negatively affect a person’s ability to think and remember.

The most common type of dementia is Alzheimer’s disease, a neurodegenerative disorder that typically affects people aged 65 or older.

The World Health Organization (WHO) estimates that Alzheimer’s disease accounts for 60–70% of dementia cases.

According to the National Institute on Aging, researchers do not fully understand why some people develop Alzheimer’s. However, they believe the reason is likely to be a combination of genetics, environmental factors, and lifestyle.

Researchers have found that someone can have biological signs of Alzheimer’s disease decades prior to developing symptoms. As a consequence, scientists are interested in exploring what factors during midlife may increase the risk of dementia.

One possible factor is multimorbidity — having two or more chronic diseases. Researchers have found that multimorbidity is common in people with dementia.

However, few previous studies have investigated whether there is a link between multimorbidity during midlife and dementia.

Medical News Today spoke with Dr. Archana Singh-Manoux, a research professor at the Université de Paris in France. Dr. Singh-Manoux is the corresponding author of the new study.

“Multimorbidity — the occurrence of two or more chronic diseases — is increasingly common and not confined to older ages. [I]t is also associated with a range of adverse health outcomes, including mortality.”

“There is quite a lot of evidence showing some chronic diseases — analyzed one at a time — [are] associated with dementia, leading us to examine the role of multimorbidity in the risk of dementia,” said Dr. Singh-Manoux.

To conduct the study, Dr. Singh-Manoux and her colleagues drew on data from 10,095 people who took part in the Whitehall II study.

This study tracked British civil servants for an average of 32 years, starting between 1985 and 1988.

When they joined the study, the participants did not have dementia and were aged 35–55.

The researchers defined multimorbidity as having at least two of the following chronic conditions: heart disease, stroke, heart failure, diabetes, hypertension, cancer, kidney disease, obstructive pulmonary disease, liver disease, depression, mental health conditions other than depression, Parkinson’s disease, and arthritis.

The researchers found that people had a 2.4 times greater risk of dementia if they had multimorbidity at the age of 55, compared with people who did not have any of the chronic conditions.

Further, the researchers found that the later a person developed multimorbidity, the weaker the likelihood of developing dementia.

Specifically, dementia risk increased by 18% for every 5 years earlier that multimorbidity appeared.

The risk associated with younger multimorbidity increased further when a person had three or more chronic conditions.

MNT spoke with Prof. Paul Morgan from the UK Dementia Research Institute at Cardiff University in Wales. Prof. Morgan was not involved in the study.

“What is special about this study is its size and reach — over 10,000 individuals followed up for 30 years with a wealth of clinical data collected. As such, its findings, though not entirely novel and not surprising to those who study dementia, are important.”

Prof. Morgan highlighted that “this study does not address causation but does strengthen the incentive for other researchers to explore the links and gives some signposts regarding direction.”

“From my own perspective, as someone who thinks that chronic inflammation is an important contributor to brain degeneration that underlies most dementias, it is interesting that the most relevant of the multimorbidities identified as risk[s] in this study are inflammatory diseases.”

– Prof. Morgan

Dr. Singh-Manoux told MNT that, despite the study not being able to demonstrate causation, its findings were significant.

“It is true that observational studies cannot demonstrate causation, but faced with diseases that have a long preclinical period, it is difficult to imagine a study design that would allow causal inference.”

“Dementia is thought to develop over a very long period, perhaps up to 20 years,” she continued, “and careful observational studies are best suited to the identification of risk factors and potential prevention targets.”

“The mechanisms underlying the association between multimorbidity and dementia are likely to involve a range of pathophysiologic alterations induced by chronic diseases. Multimorbidity at younger ages — midlife in our study — implies a longer period of exposure to these alterations, thereby increasing the risk of dementia at older ages,” explained Dr. Singh-Manoux.

Prof. Morgan and Dr. Singh-Manoux both believe that the study has implications for clinical practice.

“[T]he study emphasizes the importance of prevention and control of common diseases such as diabetes, arthritis, and heart disease, not only to reduce the direct impact of the disease but also to prevent the cumulative effect over years of multiple diseases on the brain, increasing dementia risk,” said Prof. Morgan.

Dr. Singh-Manoux agreed that prevention is important:

“Brian health is likely to be a lifelong process, and the lack of curative solutions for dementia highlights the importance of prevention, starting early in midlife. For those with a first chronic condition, it is important to manage the condition so that a second chronic condition is avoided.”

“Data from high income countries show the increasing prevalence of multimorbidity in midlife. This is likely to have implications for the cognitive status of individuals at older ages,” said Dr. Singh-Manoux.

Dr. Karen Harrison Dening, head of research and publications at Dementia UK, told MNT that people should be encouraged to adopt healthy lifestyles to reduce their risk of dementia. Dr. Dening was not involved in the study.

“From our own work with families, we know that long-term conditions ​and multiple morbidity of conditions can exist alongside ​a diagnosis of dementia.”

“Conditions like ​diabetes, cancer, heart disease, and high blood pressure, in addition to a diagnosis of dementia, can lead to families being overwhelmed by appointments, check-ups, and medication.”

“However, the risk of contracting any of these conditions can be reduced by healthy ​lifestyles as early in life as possible.”

“Health professionals have an important role to play in sharing information and advice to support healthy lifestyles — this includes eating healthily and exercising regularly. It is about promoting and ensuring accessibility of regular check-ups with [doctors] so that any health concerns can be picked up at an early stage. For those already diagnosed​ with dementia, this same support can improve well-being,” said Dr. Dening.

Dr. Singh-Manoux outlined several areas that still require research:

“There remain a number of questions. Here are three key issues: First, much larger studies are required to identify specific combinations of chronic conditions that are detrimental for cognitive health at older ages.”

“Second, the role of medication for chronic diseases and their interactions in the risk of dementia could not be examined in our study.”

“Third, we were not able to examine dementia subtypes — it would be important to link disease combinations with specific dementia subtypes,” said Dr. Singh-Manoux.

Prof. Morgan agreed: “The list of multimorbidities is long and highly diverse. Some effort was made to identify those most relevant to dementia risk.” He suggested that we should now examine this list of conditions to understand whether they all impact dementia risk in the same way, for instance through inflammation. Alternatively, he explained, these different conditions might bring individual factors that combine to increase dementia risk.

As for limitations, Prof. Morgan explained: “A weakness of the study is that “all causes” dementia is used as the readout. Dementia is not a single disease, and studies to explore the impact of multimorbidities on specific dementia types would be informative.”

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