It is not uncommon for dietary recommendations to be made on the basis of just one or two of a food’s constituents. However, most things that pass our lips are complex chemical concoctions, which means that judging foodstuffs on just a small portion of what they contain may lead to not altogether accurate assessments of their likely effects on health. I recently spied an example of this misappliance of science in the Journal of Urology. Researchers found that dosing up individuals with pure caffeine brought about biochemical changes in their urine that would be expected to increase the risk of kidney stones. As a result of this discovery, the authors recommended strict limits on tea and coffee consumption for those with a history of kidney stones. In stark contrast to this advice, however, exist several studies that link tea and coffee quaffing with lower kidney stone risk.
The apparent ability of tea and coffee to protect against kidney stones is quite likely something to do with the fact that the principle component of these beverages is water. Drinking tea or coffee will stimulate fluid flow through the kidneys and bladder ” something that is likely to reduce the risk of stones. Of course, another option for those wanting to dilute their risk of kidney stones is simply to drink more water. One study found that this simple measure reduced the chances of kidney stone recurrence by more than half.
Kidney stone risk is not only related to what we drink, but also what we eat. Stones come in several forms, with the most common being composed of the mineral calcium and a substance called oxalate. Individuals with a history of such stones may be therefore be advised to limit their consumption of calcium-rich foods (e.g. dairy products, seeds and green vegetables). However, like the recent warning regarding caffeinated brews, the recommendation to restrict calcium in the diet does not appear to be scientifically sound: studies show that individuals with higher intakes of calcium tend to be at reduced risk of calcium oxalate stones. Calcium is known to bind to oxalate in the gut, effectively barring its entry into the body. Scientists have theorised that it is through this mechanism that calcium in the diet actually protects against the formation of calcium oxalate stones.
Another route through to lowering oxalate levels in the body is to ensure a good intake of the nutrients magnesium and vitamin B6, as both of these help in the conversion of oxalate into other substances that do not contribute to stone formation. Nuts are rich in both magnesium and B6, and also contain useful quantities of the mineral potassium which has also been linked with a reduced risk of kidney stones. Other good sources of potassium include fruit and vegetables.
Studies in which individuals have supplemented with vitamin B6 and/or magnesium have generally produced promising results, with one study showing that a combination of these two nutrients reduced kidney stone recurrence by 90 per cent. For those seeking to optimise protection, I recommend supplementing with 400 ” 500 of magnesium and 25 ” 50 mg of vitamin B6 each day. The evidence suggests that nutritional approaches help ensure that those prone to kidney stones have no hard feelings.