What it is
Vitamin D (D₂ or D₃) is fat-soluble, stored in body tissues. Many people supplement it for bone health, immune support etc.
How it harms
High vitamin D → hypercalcaemia (too much calcium in blood) → deposition of calcium in renal tubules → kidney stones, nephrocalcinosis, impaired kidney function.
Liver: excessive vitamin D means higher workload in the liver for metabolising, and calcium overload can harm hepatic microcirculation. Also, fat-soluble vitamins in excess generally burden the liver.
Key risk factors
High‐dose supplementation without monitoring (e.g., > 4,000 IU/day for adults unless supervised).
Poor kidney function (makes dealing with calcium harder).
Using vitamin D plus high calcium intake or other supplements that raise calcium.
How to protect yourself
Get your vitamin D blood level measured before high-dose use.
Use only the dose recommended by your doctor.
Monitor calcium, kidney function, and watch for kidney stone history.
3. Iron Overload (Excess Iron Supplementation)
What it is
Iron is essential but supplementing when not needed can cause “iron overload”.
How it harms
The liver stores excess iron (in ferritin/hemosiderin). Over time this can cause liver inflammation, fibrosis, cirrhosis.
Kidneys: Iron excess creates oxidative stress and may damage glomeruli or tubules; though less directly, overload conditions can affect kidney structure.
Key risk factors
Taking iron supplements without iron deficiency or doctor supervision.
Genetic conditions like haemochromatosis (iron-storage disease).
How to protect yourself
Test ferritin and transferrin saturation before supplementing iron.
Avoid taking iron when not needed.
If supplementing, ensure periodic check of liver function.
4. High doses of Vitamin C (Especially in certain forms)
What it is
Vitamin C (ascorbic acid) is water‐soluble and generally lower risk than fat‐soluble vitamins. But very large doses may cause kidney issues.
How it harms
Excess vitamin C is metabolised to oxalate; high urinary oxalate may lead to calcium-oxalate kidney stones.
Kidneys bear the burden of excreting excess; in people with reduced kidney function the risk is greater.
Key risk factors
Very high supplementation (e.g., >1 g/day, especially chronically).
History of kidney stones or reduced kidney function.
How to protect yourself
Stay within safe limits (e.g., ~ 200-500 mg/day unless directed otherwise).
Hydrate well (water helps flush oxalate).
Avoid combining large doses of vitamin C with other stone‐risk nutrients (e.g., high calcium).
5. Fat-soluble vitamin “stacking” (Vitamins A, D, E, K)
What it is
When you take multiple supplements that contain fat-soluble vitamins, you might unintentionally exceed safe limits collectively.
How it harms
As these vitamins accumulate in tissues and liver, excess burdens liver metabolism and storage capacity.
The liver is the central processing organ for fat‐soluble vitamins; increments in storage can lead to hepatotoxicity or liver dysfunction.
Downstream from that, kidney function may suffer because liver dysfunction affects fluid, electrolytes, and toxin removal.
Key risk factors
Taking several multivitamins + individual fat-soluble vitamin pills.
Using “megavitamin” formulas that deliver many times the Recommended Dietary Allowance (RDA).
How to protect yourself
Check the total intake of each fat‐soluble vitamin (from diet + supplements).
Avoid using multiple products that provide overlapping fat-soluble vitamins unless supervised.
Monitor liver enzymes if you routinely use high-dose fat‐soluble vitamins.
