The human kidneys filter more than 180 litres of fluids containing blood, waste products such as creatinine, excess water, and toxins, every day. Kidneys remove these fluids with the help of tiny filtering tubes called glomeruli. A healthy kidney can filter waste from the blood at a rate of 90 millilitres (mL) per minute or more, which is termed glomerular filtration rate (GFR). However, in the case of chronic kidney disease, the kidneys progressively lose their ability to filter effectively, resulting in a waste build-up in the body. A recent study published in the journal Neurology on 5th May 2021, stated that this decline in kidney function can increase the risk of dementia in older people.

The study: Determining the brain-kidney connection

Scientists analysed the medical data of more than 329000 patients (aged 65 years and above) who received medical treatment, in Stockholm. None of the patients had a history of dementia or kidney disease. Dementia is a syndrome characterised by a progressive deterioration in memory, behaviour, and the ability to think and perform everyday activities. The patients were followed up for 5 years. from 2006 to 2011.

Blood tests were conducted to determine the levels of plasma creatinine (secreted by the muscles and released in urine) and the glomerular filtration rate (GFR) of each participant. Low GFR indicates poor functioning of kidneys.

The study aimed at determining the rate of dementia in people with different levels of kidney function. 

Note: The numbers were measured in person-years. Person-years involves both the number of people in the study and the amount of time each person spent in the study. For instance, if a study follows 1000 people for 1 year, the data would be measured in 1000 person-years.

Results of the study

The results of the study showed that:

• After following up for 5 years, 18,983 participants (around 6%) developed dementia. 
• Scientists found that the cases of dementia increased as the GFR decreased. In people with:
  • GFR of 90 to 104 mL per minute, 7 cases of dementia were reported per 1,000 person-years. 
  • GFR of 60 to 89 mL per minute, 15 cases of dementia were reported per 1000 person-years.
  • GFR of 30 to 59 mL per minute (indicates moderate chronic kidney disease), 26 cases of dementia were reported per 1000 person-years.
  • GFR of less than 30 mL per minute (indicates severe chronic kidney disease), 30 cases of dementia were reported per 1,000 person-years.
• Scientists stated that people who developed moderate and severe chronic kidney disease had a 71% and 162% (respectively) higher risk of suffering from all-cause dementia as compared to people with normal kidney function. 

The scientists further examined the data of more than 200,000 participants (who got multiple blood tests done during the study) to determine the role of the rate of kidney function decline in the development of dementia. The results showed that the faster the decline in GFR, the higher the risk of developing dementia.

With this study, scientists concluded that at least 10% of dementia cases occurred in people with a GFR of less than 60 mL per minute. Scientists suggest that doctors should develop appropriate strategies to screen and monitor dementia in people diagnosed with chronic kidney disease and vice versa.  

How to keep the kidneys healthy

Measures that may help improve kidney function include: 

• Hydration: Drinking enough water would not only keep the body hydrated but also helps in removing harmful toxins from the body. Straw-coloured urine indicates that the body is well-hydrated. 
• Maintain blood pressure: High blood pressure increases the risk of developing chronic kidney disease. Thus, blood pressure should be maintained by reducing the consumption of salt and alcoholic beverages, drinking enough water, and exercising regularly. Blood pressure value between 90/60 mm Hg and 120/80 mm Hg is considered normal.
• Keep monitoring blood sugar levels: High blood sugar (hyperglycemia) or diabetes can damage the tiny filtering units of the kidneys, ultimately resulting in kidney failure. Hence, it is important to keep checking blood sugar levels frequently using a glucometer.
• Quit unhealthy habits: Smoking cigarettes and drinking alcohol increases blood pressure and decreases the blood flow to the kidneys. Therefore, quitting smoking completely and limiting the consumption of alcohol significantly is advisable. 
• Reduce cholesterol levels: Decrease the consumption of saturated fats, which are found in red meat and fatty dairy products. Also, avoid foods rich in trans fats, such as baked and frozen foods, as they increase the levels of bad cholesterol (LDL) in the body. These can clog the renal arteries and hamper the blood supply to the kidneys.
• Consume a healthy diet: A balanced diet rich in fruits, vegetables, whole grains (found in whole wheat pasta, bread and rice), and nuts and seeds can help in maintaining weight and blood pressure. Avoid consuming excessive salty and fatty foods as they can negatively affect the kidneys. People with weak kidneys can switch to a low protein or plant-based diet as it puts less strain on the kidneys.
• Stay physically active: Maintaining a healthy weight can help the kidneys function better. Practise moderate-intensity exercises, such as brisk walking, cycling or swimming, for at least 150 minutes a week or 30 minutes a day.
• Use painkillers with caution: Prolonged or overuse of over-the-counter available painkillers such as ibuprofen and naproxen (common Nonsteroidal anti-inflammatory drugs) can damage the kidneys. Therefore, take these medicines only after consulting a medical professional and drink plenty of water while taking them. 

Takeaway

Since there is no effective treatment for dementia, it is important to learn about the modifiable risk factors of the disease and take preventive measures. Though scientists in this study tried to establish the correlation between low kidney function and dementia, further research is needed to prove if preventing or treating kidney diseases can help prevent the occurrence or delay the progression of dementia.

It is, however, advisable to reduce the risk of developing kidney disease by consuming a healthy diet, exercising regularly, maintaining a healthy weight, quitting smoking, and limiting alcohol consumption. One must keep their blood pressure and blood sugar levels within the normal limits to ensure the proper functioning of the kidneys. 

For any questions on kidney health, you can talk to a nephrologist.