Which supplements are risky in the presence of kidney damage?
Yes, multiple supplements are demonstrably risky in the presence of kidney damage. Herbal preparations (particularly those containing aristolochic acid), germanium supplements, and high doses of vitamin D or C stand out the most; if you already have kidney problems, discuss every supplement with your doctor.
Herbal preparations containing aristolochic acid, a substance found in certain Chinese herbal remedies, are the best-supported causes of kidney damage. The damage is serious, sometimes permanent, and can lead to complete kidney failure. Herbal preparations in general also pose a broad risk: contamination with heavy metals, mislabelling, or direct plant toxins can cause acute kidney failure, kidney stones, or chronic scar tissue in the kidneys. In people who already have kidney damage, dangerously high potassium levels and rises in blood pressure are additional concerns.
Germanium supplements, sometimes marketed as immune boosters, have caused serious kidney failure in eighteen documented individuals, two of whom died. After discontinuation, kidney function did not fully recover. This is a supplement with no proven benefit and serious risks; avoiding it is the only logical choice.
Excessively high doses of vitamin D can cause kidney damage through an accumulation of calcium in the body. This does not apply to normal supplementation, but with prolonged use of heavily dosed preparations (in the category of hypervitaminosis) the risk is real. High doses of vitamin C pose a similar risk, particularly if your kidneys are already not functioning optimally.
Creatine supplements are more nuanced. They temporarily raise a blood value (serum creatinine) that doctors also use to measure kidney function, which can create a false impression of kidney damage. In healthy people this is probably a measurement distortion, not actual damage. However, in people with pre-existing kidney damage or who are taking medications that place a burden on the kidneys, creatine is not recommended, as complications have been described in those cases. Amygdalin, also sold as 'vitamin B17', also has toxic potential for the kidneys, but has been less thoroughly studied.
In acute kidney damage, moreover, any supplement, including seemingly harmless vitamins and minerals, can disrupt the body's balance. Both deficiencies and excesses are dangerous when kidney function is severely reduced. Anyone with kidney damage would do well to always discuss supplementation with a doctor or pharmacist first.
This answer draws on several review articles, including nephrological and toxicological overviews. The evidence for aristolochic acid and herbal preparations is strongest; for germanium, eighteen cases are well documented. For creatine, vitamin C, and vitamin D the body of evidence is narrower; for amygdalin the evidence is thinnest and no large numbers of documented cases have been described.
Do you need to restrict protein intake to protect your kidneys?
If your kidneys are healthy, you do not need to restrict your protein intake. If you have chronic kidney disease, discuss with your doctor and dietitian whether a protein-restricted diet is worthwhile, because too little protein is also dangerous.
Is eating a lot of protein bad for your kidneys?
For healthy people, kidney damage from eating a lot of protein has not been demonstrated. If you already have kidney disease, the amount and type of protein matter: discuss this with your doctor or dietitian.
How do I keep my kidneys healthy as I age?
Even a mild decline in kidney function clearly raises the risk of serious health problems. The available studies focused on measuring those risks, not on what you can do yourself to prevent that decline.
Do your kidneys age at a different rate than your liver?
The kidneys age measurably faster than the liver, but for most healthy people that decline only has major consequences when dosing medications at an advanced age. If you also have high blood pressure or diabetes, it is wise to have your kidney function checked regularly.
How harmful are microplastics in your body to your health?
Microplastics demonstrably accumulate in your organs and are associated with signs of inflammation and reduced sperm quality. How harmful that actually is, we do not yet know.
Do GLP-1 agonists increase the risk of gallstones and pancreatitis?
GLP-1 agonists measurably increase the risk of gallstones, but the risk of pancreatitis does not appear to be elevated in the larger studies. If you already have gallstones or have had pancreatitis before, discuss this explicitly with your doctor.