I've been researching various supplements and their effects on kidney health, and some of the information regarding white willow bark is a bit concerning. I have found from multiple online sources that willow bark can actually cause kidney damage, particularly in those that already have kidney disease. Some concerning bits pulled from multiple sources posted below:
Kidney disease: Willow bark might reduce blood flow through the kidneys, which might lead to kidney failure in certain people. If you have kidney disease, don’t use willow bark.
Because willow bark contains between 8 and 20% tannins (above 10% can be harmful), a higher concentration than in most other plants, there is an increased risk of adverse effects including upset stomach, nausea, renal damage, and esophageal and nasal cancer with long term use.
Some researchers suggest that people with asthma, diabetes, gout, gastritis, hemophilia, stomach ulcers, or with kidney or liver issues should also avoid willow bark.
What are your thoughts on the preceding information? Given the stress that all of our kidneys tend to undergo from our lifestyle, especially when on cycle, does willow bark seem like a safe item to be ingesting?