The article “A Rise in Kidney Stones Is Seen in U.S. Children” was recently featured in the New York Times.
The article reported what is a perceived increase in kidney stones in children and attempted to explain the phenomenon based on changes in lifestyle. The idea is that, as the genetics of the population have not changed significantly, increases in kidney stones can be attributed to changes in the environment.
Generalizing from what is known about kidney stones in adults, I will briefly expand on the points made in the article so that the reader has a fuller view of how our lifestyle today (a life of excess, if I may) contributes to kidney stones.
Below is a brief list outlining the topics to be discussed over a series of entries:
Be aware: while for many people kidney stones are preventable, there are, however, underlying metabolic and medical causes of kidney stones, and kidney stones are a reason for evaluation by your physician.
Kidney stones are the aggregation of crystals in the urine
One way to conceptualize how kidney stones are formed is to think back to the experiment you did in grade school in which while stirring water you slowly added more and more salt. Initially, the additional salt fully dissolved in the water, but a point arose when the water could no longer hold any more salt, when the sodium suddenly precipitated out and crystals developed. While this is an overly simplistic analogy for how kidney stones form (the urine, for instance, contains molecules such as citrate that attempt to prevent the formation of crystals or kidney stones), it can be a useful one.
The analogy clearly is useful in understanding how a lack of sufficient water intake predisposes people to the formation of kidney stones and how drinking more water is the best way to prevent kidney stones. The more water we drink, the more we dilute our urine and the greater difficulty crystals have in aggregating.
How much fluid to drink?
The more important question, of course, is how much should people urinate or how dilute should the urine be. The recommendation is that people with kidney stones should pass a little over 2 liters (~1/2 gallon) of urine per day, which amounts to drinking ~ 3 liters of fluid per day. Also, because a concentrated urine at any time of the day still predisposes to kidney stones, the fluid intake should be spaced throughout the day, including at night. Those living in hotter climates or engaged in heavy exercise likely need to drink more, as they are losing much of the water in ways other than through the kidneys, such as through the skin by sweating.
A rule of thumb: if the urine of a person with kidney stones looks like water (clear, not yellow) throughout the day than that person is drinking enough water.
Caution: there are dangers to drinking too much water (please consult with your doctor), and those of us not predisposed to kidney stones do not need to meet those amounts.