If the urinary volume is low, and/or if the urine is more concentrated than is desirable, minerals and other substances in the urine may crystallise in the kidneys, and in time aggregate to form a stone.
The vast majority of kidney stones are comprised of calcium oxalate or calcium phosphate. Uric acid, struvite and cystine stones are less common.
Factors that contribute to the formation of kidney stones may include:
- Low fluid consumption, causing the urine to become more concentrated and increasing the likelihood of crystals forming
- High levels of calcium, phosphate, oxalate or uric acid in the urine
- Low levels of chemicals called stone inhibitors in the urine
- Parathyroid gland overactivity
- A personal or family history of kidney stones
- Chronic or recurrent urinary infections
- The use of certain medications
- Structural or metabolic abnormalities in the kidneys or elsewhere in the urinary tract
Consuming a diet that is low in fibre, or contains excessive quantities of refined carbohydrates, animal protein, alcohol, or fats may increase the risk of developing calcium-containing kidney stones.
Other dietary factors may include consuming excessive amounts of oxalates, soft drinks (especially cola), alcohol (especially beer), caffeine, salt, or vitamin D. Low levels of magnesium (especially in relation to calcium), potassium or vitamin B6 may also be a factor. Either excessive and inadequate consumption of calcium may contribute to the formation of kidney stones.
Eating large quantities of fruit and vegetables appears to convey a degree of protection, as does being vegetarian.