Kidney stones common in France

A French study analyzing over 51,000 kidney stones found that calcium oxalate crystals make up about 80% of all kidney stones, with nearly 72% of stones composed of this substance. In France, about 10 to 12% of the population is affected, and the frequency of kidney stones has been rising for about fifty years in industrialized countries.

Men more likely to be affected

Men aged 20 to 60 are twice as likely to be affected by kidney stones as women, a detail that continues to puzzle researchers. This gender disparity is not fully understood and remains a focus of ongoing studies.

Oxalates in common foods

Foods such as spinach, beets, almonds, nuts, and dark chocolate are naturally rich in oxalates, compounds found in many plants. Once ingested, these oxalates pass into the intestine, where they can be absorbed and then filtered by the kidneys.

Calcium and oxalate interaction

The problem arises when these oxalates meet calcium present in urine, forming calcium oxalate crystals. This interaction is a key factor in the formation of kidney stones, particularly in individuals with certain dietary habits.

Dietary calcium and stone formation

A paradox exists in the fact that many French people, aiming for a healthier diet, have reduced or eliminated dairy products, which are a source of calcium. This exclusion of dietary calcium works against the kidneys, as calcium in the intestine binds to oxalic acid to form insoluble complexes that are eliminated directly through stools.

Impact of calcium intake on recurrence

A five-year study on men prone to recurrence showed that among those following a low-calcium diet, nearly four out of ten reformed stones, compared to about one in five in the group that maintained a normal calcium intake. This result, confirmed by a 2002 study by Italian researcher Borghi, challenged common beliefs about the role of calcium in kidney stone prevention.

Optimal meal timing for prevention

The solution is to consume calcium and oxalates during the same meal, allowing calcium to bind oxalates in the intestine, where they are eliminated through the stools instead of flowing to the kidneys. This practice reduces intestinal absorption of oxalates by 30 to 50%.

Prevention guidelines

Recommendations for preventing stone recurrence are based on three pillars: drink enough to produce more than two liters of urine per day, maintain a normal calcium intake between 800 and 1,200 mg per day, and limit salt to around 4 to 5 grams per day.

Hydration alone may not prevent stones

A recent American study on connected water bottles intended to encourage drinking more did not show a significant effect on recurrences despite a real increase in water consumption, suggesting that the prevention of stones is not simply a hydric reflex.

New insights into stone formation

Studies published in the PNAS journal recently revealed the presence of live bacteria at the very heart of calcium oxalate stones, suggesting that their formation may not be as purely chemical as previously thought. This discovery opens new avenues for understanding and treating kidney stones.