For years, evidence has been mounting that suggests that chronic kidney disease and dementia are linked. The mechanisms behind this are poorly understood, because the breadth and depth of the connection are strong enough that any simple explanation doesn’t address the whole picture. We’ll look at the intricacies of this interplay, as well as possible causes, and what to do about it.
What Is Kidney Disease?
Chronic kidney disease (CKD) is a progressive condition where the kidneys don’t function as well as they should. The most common causes are diabetes and high blood pressure. Kidney disease progresses through stages, defined by how well the kidneys are working. The final stage is stage 5, also known as end-stage renal disease, or ESRD. During ESRD, the kidneys have stopped working. Their function is taken over by a filtration machine in a treatment called dialysis.
How Does Kidney Disease Affect the Brain?
Several studies over the years have shown a link between ESRD and cognitive impairment. This might suggest that something about kidney failure—or perhaps the dialysis treatments that go with it—is responsible for cognitive decline and dementia. However, this cognitive impairment isn’t just limited to ESRD. People in all stages of chronic kidney disease have shown signs.
There are many factors in kidney disease that could theoretically affect the brain. High blood pressure is both a cause and a symptom of chronic kidney disease. High blood pressure is also known to cause a wide range of neurological symptoms, due to the risk of blocking blood from accessing the brain. Aside from high blood pressure, kidney disease can lead to buildup of various toxins and waste products in the blood, and some of these, like Cystatin-C, seem to affect brain function, as well.
Finally, kidney disease increases the risk of urinary tract infections (UTIs). Among older people, UTIs are associated with acute bouts of confusion and altered behavior known as “delirium”. This can look very similar to dementia.
How Does Dialysis Affect the Brain?
While we know that kidney disease can affect brain function on its own, dialysis also has an undeniable effect. Long-term studies of people on dialysis show an increase in risk of dementia, and that prevalence increases over time. The rate of dementia among dialysis patients is 21% for men, and 25% for women.
This effect is particularly noticeable on hemodialysis. The good news is that other types of dialysis are available. People on peritoneal dialysis experience dementia at a rate 25% lower than those on hemodialysis. It’s also possible that more frequent hemodialysis can lower the risk of dementia, just as it does for other cardiovascular symptoms.
Why is hemodialysis linked to cognitive decline? One of the leading theories is that it has to do with the sudden drop in blood pressure. Kidney failure causes excess fluid and toxins to build up in the body, such as creatinine, a waste produced by muscles when they’re worked. This fluid and waste buildup raises blood pressure, which can cause problems throughout the body, including increased risk of congestive heart failure.
Dialysis removes this excess fluid, since the kidneys can’t, keeping patients within a healthy creatinine range. But when someone dialyzes 3 or 4 times a week, that gives them a lot of time in between each treatment for that fluid to build back up. Not only is the fluid buildup harmful, but removing it so abruptly may be harmful, as well. This sudden loss of blood pressure can “shock” the heart, and it may have a negative effect on other organs in the body, as well.
Potential Causes of Cognitive Impairment in Patients with CKD
There are many risk factors for cognitive decline that are also tied to kidney disease and dialysis.
- High blood pressure, as mentioned earlier, is a risk factor for both cognitive impairment and CKD
- Diabetes is also a leading cause of CKD and a risk factor for cognitive impairment
- Sleep disturbances
- Malnutrition is common among people on dialysis. While the need for protein increases, appetite often decreases.
- Calcium and phosphate buildups occur when the kidneys can’t remove these substances from the blood fast enough.
- Uremia happens when a waste product called urea builds up in the blood
- Sodium and water retention are both a cause of high blood pressure and a result of CKD.
These factors (and others) form an interconnected web of symptoms that need to be carefully managed to protect blood pressure, kidney function, and brain health.
The Vascular Hypothesis of Cognitive Impairment
The vascular hypothesis was first proposed 25 years ago, and evidence to support it has been mounting ever since. It suggests that decreased blood flow to the brain is a cause of cognitive impairment and Alzheimer’s. This idea has been supported by decades of research, including studies that use brain imaging to determine how much blood is reaching a person’s brain. That means that this hypothesis is helping doctors assess risk and treat people right now.
We don’t know whether kidney disease causes this, or if the two of them happen together. The network of blood vessels that supply the kidneys and brain are similar, so it’s possible that a larger problem affecting those blood vessels causes kidney disease and cognitive impairment at the same time. In any case, it’s a useful tool for doctors to have when they’re determining someone’s risk of dementia.
What Can you do to Limit Your Risk of Dementia with Kidney Disease?
There are several things that you can do to minimize the risk of dementia with kidney disease and dialysis. One of those is to choose a home dialysis option. Peritoneal dialysis has been consistently shown to have less of a negative effect on cognitive function. And while there isn’t as much research on the benefits of more frequent hemodialysis (which can be enabled by home dialysis), the research that does exist is promising. Moreover, there is significant research that tells us more frequent hemodialysis has benefits for blood pressure and other organ health.
- Choose foods with omega-3 fatty acids, like fish and eggs. You may also consider a supplement. (Just talk to your care team before taking any supplement to make sure that it’s safe for you.) Omega-3 fatty acids, especially docosahexaenoic acid (DHA), are good for your brain health. They’ve been shown in numerous studies over the years to slow age-related cognitive decline, dementia, and even Alzheimer’s. The more you can do for your cognitive health, the better off you are.
- Stay active. Exercise releases endorphins that can improve your mental health. (People on dialysis often describe experiencing depression) Exercise is also good for your cognitive ability. It increases the flow of nutrient-rich blood throughout the body, including the brain. And it can actually influence the structure and function of your brain in ways that improve cognition. These effects are profound, and long-lasting. Not to mention, the physical effects of exercise can improve some of the other symptoms around CKD, such as blood pressure, which benefits your brain and your health overall.
- Limit sugar intake. Sugar intake is an enormous risk factor for diabetes, which in turn is one of the biggest causes of chronic kidney disease. If you’re already receiving treatment for kidney disease, be sure to adjust your diet to get the appropriate amounts of protein, phosphorus, and sodium. All of these can worsen CKD symptoms, which in turn affects blood pressure and brain health.
CKD and the Mind
The research on dementia and CKD can certainly look concerning. But the good news is that now that we know about the connection, and know ways to limit it, we have a better shot at protecting ourselves than ever before. Knowing what factors in to brain health and knowing how to take care of yourself with the right kinds of dialysis, physical activity, and smart dietary choices, can help you make the most of your time on dialysis, and be the best, healthiest you that you can be.
Jenny Hart is a health and wellness writer with a passion for travel, cycling and books. Her focus is topics related to the effects of aging on health and she is interested in research that can help people age better. When she isn't writing or travelling, she's traversing NYC with her two dogs Poochie and Ramone.
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