Memory researchers have long been searching for early warning signs indicating the development of Alzheimer’s disease or other types of dementia. The latest scientific studies are leading them to an unlikely place, or should I say organs… the kidneys.
Let’s take a closer look at the evidence that points to a connection between declining kidney function and the development of dementia.
The kidneys are resilient organs. So much so that as much as 90 percent of kidney function can be lost before symptoms of kidney damage become apparent.
In fact, 37 million Americans already suffer chronic kidney disease (CKD), described as a persistent reduction in kidney function. These cases are mostly related to conditions such as diabetes and high blood pressure. Still, it’s surprising to hear that more than half of people over the age of 75 are believed to have kidney function that’s below normal.
What’s more, even a mild reduction in kidney function will allow waste products to remain in the bloodstream, and this, together with other consequences of reduced kidney function, is linked to an increased risk of cardiovascular disease.
But what about the brain? Studies have provided conflicting results. To get some clarity, researchers from the Karolinska Institute in Stockholm, Sweden, conducted a large study.
The Five Stages of Kidney Function
The Sweden trial involved 329,822 participants aged 65 or older with no history of dementia. This is larger than all other previous studies on kidney and brain function combined.
Each participant provided blood samples that researchers tested for creatinine. Creatinine is a waste product of muscle metabolism that’s filtered out by the kidneys into the bladder and urine. How well the kidneys are able to do this is one indicator of kidney performance.
Considering these results together with the participant’s age, gender and other factors, scientists are then able to calculate the estimated glomerular filtration rate (eGFR), or the ability of the kidneys to filter out waste.
A normal eGFR is over 90 percent, meaning that the kidneys are able to filter wastes from the blood at a rate of over 90 milliliters (ml) per minute.
This is stage one of kidney function and is considered normal. The other stages of kidney function are:
- Stage two: mildly decreased kidney function (60 to 89 percent)
- Stage three: mild to moderately decreased kidney function (30 to 59 percent)
- Stage four: severely decreased kidney function (15 to 29 percent)
- Stage five: kidney failure (under 15 percent)
71 Percent Greater Risk of Dementia
Over the follow up period of five years, 18,983 of the participants in the Sweden study were diagnosed with dementia.
After adjustments for factors that could influence the results, such as smoking, alcohol use, high blood pressure and diabetes, the Swedish scientists found the incidence of dementia went up progressively as eGFR declined.
For example, those with stage three (mild to moderate) filtration rate had a 71 percent increased risk of dementia compared to those with kidney function at stage one (normal). Those in stage four (failing) kidney function had greater than 2.5 times the risk of dementia (162 percent). These subjects were also more likely to suffer vascular dementia than Alzheimer’s disease.
After some additional analysis, which added credibility to the researchers’ findings, they found a steep decline in kidney function within a year was also linked to a higher risk of dementia.
To conclude their report, which has just been published in the journal Neurology, the Swedish team considered that as many as ten percent of dementia cases could be attributed to an eGFR in stage three kidney function or below.
“A proportion higher than that attributed to other dementia risk factors such as cardiovascular disease and diabetes,” they wrote. In other words, your kidney function may be even more important to your memory than your heart health!
This study highlights the importance of routinely checking kidney function, particularly since, as the authors write, “awareness of CKD is still very low among patients and physicians…”
Strategies for keeping your kidneys healthy and well-functionig include drinking adequate amounts of water each day, minimizing processed foods and eating plenty of fruits and vegetables. It’s also critical to keep a watch on your blood pressure and blood sugar levels, as well as maintain a healthy weight.