Water intake and kidney stones
Kidney stones, also called urolithiasis, are a common pathology affecting about 10% of the population in developed countries at least once in an individual’s lifetime. Recent trends show an increase in stone prevalence.
The role of dietary habits, including fluid intake, has a great implication in stone development.
Hydration: A well recognized role in recurrence prevention
The role of increased fluid intake as a means of preventing recurrence of kidney stones is well recognized today. In fact, it has been used since the time of Hippocrates.
Adequate fluid intake helps to decrease concentrations of substances involved in stone formation thus reducing their saturation degree in urine (a necessary condition for crystallization, and a first step towards stone formation).
Many studies have shown the beneficial effects of improved fluid intake (and consequently urine volume) on stone recurrence prevention.
The strongest scientific evidence certainly comes from a five-year randomized controlled trial conducted amongst patients recruited directly after their first idiopathic calcium stone episode. This study showed that recommending patients to increase fluid intakes to achieve a urine volume superior to 2L per day resulted in reduced kidney stone recurrence compared to a group without specific advice¹.
The European Association of Urology² recommends increasing fluid intake independent of the type of stones to achieve a urine volume of more than 2L a day, on top of other dietary and lifestyle advice.
Recommendations to lower the risk of kidney stones²
Is there a role of hydration for first stone prevention?
Several studies suggest that chronic dehydration from different causes such as working in a hot environment or physical exertion increases the risk of stone incidence³ ⁷. Data suggests also that stone diseases occur more frequently in geographic areas with a hot climate. In countries such as Saudi Arabia, over 20% of the population develop renal stones whereas the risk of the disease is only 12 to 13% in North America and 5 to 10 % in Europe⁸. There is also a seasonal variation of stone incidence, with higher rates in summer⁹ ¹⁰.
In addition, some studies show the relationship between fluid intake and stone risk in the healthy population:
- In two large observational studies, total fluid intake was significantly and negatively associated with the risk of renal stones¹¹ ¹².
- A three-year intervention controlled trial tested the preventive effect of an educational program on adequate fluid intake in a population living in a hot climate compared to a similar population who did not receive any advice. Results showed that the population with the educational program had a higher urine volume and a lower stone incidence than the population who were not advised on fluid intake¹³.
It has also recently been shown that an additional water intake of 1.3 L could decrease the theoretical risk of crystallization, the first step of stone formation, in the urine of a healthy population as measured by the Tiselius crystallization risk index¹⁴.
Nevertheless, further studies are needed to confirm the role of adequate fluid intake for first stone prevention.