The relationship between age-related kidney failure and neurodegeneration is interesting to consider in the context of research into the longevity-associated gene klotho. Overexpression of klotho slows aging, while loss of expression accelerates aging. Klotho also affects cognitive decline; more klotho slows age-related neurodegeneration. Klotho, however, appears to act in the kidney, not the brain. This is a point of emphasis on the importance of the kidneys to long term health; loss of kidney function leads to deterioration of tissue function throughout the body, due to the failure to clear waste products from the bloodstream.
A new study has found that people with reduced kidney function may have an increased risk of developing dementia. Chronic kidney disease affects approximately 15% of adults in the United States and it is more common as people age. However, since many people don't experience symptoms until later stages, it is estimated that 90% of people with chronic kidney disease don't know they have it. "Even a mild reduction in kidney function has been linked to an increased risk of cardiovascular disease and infections, and there is growing evidence of a relationship between the kidneys and the brain."
Researchers used a database to identify nearly 330,000 people 65 years and older who received health care in the city of Stockholm and were followed for an average of five years. None of the participants had dementia or had undergone kidney transplants or dialysis at the start of the study. Over the course of the study 18,983 people, or 6% of participants, were diagnosed with dementia.
Researchers found as kidney function decreased, the rate of dementia increased. In people with a normal kidney filtration rate of 90 to 104 mL per minute, there were seven cases of dementia per 1,000 person-years. In people with severe kidney disease, or a filtration rate of less than 30 mL per minute, there were 30 cases of dementia per 1,000 person-years.
After adjusting for other factors that could affect dementia risk like smoking, alcohol use, hypertension and diabetes, researchers determined that people with filtration rates of 30 to 59 mL per minute, which indicates moderate chronic kidney disease, had a 71% higher risk of developing dementia compared to those with normal kidney function, and people with filtration rates of less than 30 mL per minute had a 162% higher risk.