Healthy Pilot #8: Let’s Talk About Your Kidneys

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What you can do about a kidney stone if you have one, and how to avoid one if you think you're susceptible.



A kidney stone will present with lower back pain. If you experience this, it's time to cancel your flying for the day until you get can get it checked.

You've focused intently on pre-flighting the airplane,  and you've paid attention to passenger safety and comfort. But that twinge in your lower back as you line up on the centerline gives you a moment's pause. Taxi back to the ramp or press on? If it's a kidney stone, and the pain only gets worse at altitude, you'll wish you'd listened to that little voice in your head suggesting a call to your doctor instead of that morning's fly-in pancake breakfast.

Funny aches and pains are all a part of the IMSAFE mnemonic we won’t bore you with. Today's focus is on what that pain might be, and if it turns out to be a kidney stone, you'll be glad you stayed on the ground. "Kidney stones and blood in urine" are item 18j on the new Basic Med Checklist. 

If you’ve ever had a kidney stone, you’ll agree the experience is…memorable. It feels like someone has taken a baseball bat to your back, with a sharp pain that grows and radiates, sending most first-time sufferers to the ER. Emergency department staff will likely order an X-ray or CT scan and you’ll see your tormenter as a bright point heading merrily down your ureter towards the bladder.

You might get a bit of respite when it leaves the ureter, but you know it will have to pass in the way nature intended. Any attentive urologist will give you a nice screen cup to capture the little bugger when the moment arrives. And after you’ve picked yourself off the floor, you’ll be amazed that this little meteorite could cause so much havoc.

Bottom line: You’ll want to ease the passing of a kidney stone if you can, and forestall its occurrence if family history or gustatory predilection suggests it may be your turn to have one.

What To Do

We’ve once again turned to our sister site University Health News for some guidance. Basic navigation is in order:  There are four types of kidney stones, but the most common are made of calcium oxalate.

Most people believe kidney stones are the result of eating too much calcium-rich foods, or taking too many calcium supplements. Rather, failure to adequately hydrate is the most common reason. When you don’t drink enough fluid, your urine becomes concreted into stone-forming substances.



Kidney stones are irregularly shaped crystals of varying size and density.

Your first clue you may be the rich, brown hue of your urine, indicating the presence of blood. A trip to the doctor may result in an X-ray or a CT scan or ultrasound to locate the stone and rule out other possible sources of pain. Conventional treatment of symptomatic kidney stones includes pain medication and oral or intravenous fluids to help the stone on its way.

In extreme cases, your doctor may order surgery. Lithotripsy, or shock treatment to break up the stone, is usually not recommended, as it’s associated with potential adverse effects to kidney function.

To prevent a recurrence, conventional medical guidelines call for drinking at least two liters of fluid during the day. Drug treatments may include thiazide diuretics, potassium citrate or allopurinol.



A kidney stone will show up clearly on a CT scan.

Intake vs. Outgo

If you’re experiencing a kidney stone, or prior history suggests you may be susceptible, the experts at University Health News offers some guidance:

  1. Increase fluid intake. All stone formers need to drink enough fluid to achieve a total urine volume of at least 2.5 liters over 24 hours. The total amount you need to drink to excrete 2.5 liters of urine per 24 hours will vary, depending on your diet, activity level, kidney function, and other factors. For most people, drinking 2 liters of fluids is needed to excrete that much urine. If you have no idea how much urine you excrete, do a 24-hour collection and measure the total yourself.
    Pure, filtered water is best. Adding fresh squeezed lemon, lime, or unsweetened cranberry juice to the water may be more beneficial than plain water for preventing stones. These juices contain the highest amounts of citric acid and thus increase the citrate concentration of the urine. Citrate is a powerful inhibitor of the crystallization of calcium salts and higher urinary citrate concentrations reduce the formation of calcium stones.
    Another fluid option is coconut water, which is high in potassium. Potassium reduces urinary calcium excretion and people who eat high amounts of dietary potassium are at lower risk of forming kidney stones.  Do not drink soda or other sugar- or fructose-sweetened beverages. These are associated with a higher risk of kidney stone formation.
  1. Swap meat for veggies. Reducing your meat intake or switching to a vegetarian diet lowers the risk of kidney stones. Animal protein sources such as beef, chicken, and fish increase the risk of calcium oxalate, uric acid, and cysteine stone formation. Animal protein increases the acid load of the diet. The higher the dietary acid load, the higher the acidity of the urine and the higher the risk of recurrent kidney stones. The DASH-style diet, which is not vegetarian but is low in animal proteins and salt, moderate in low-fat dairy, and high in fruits and vegetables, markedly decreases the risk of stone formation. Anytime you decrease your meat intake, it is always best to do so in conjunction with increased vegetable intake since vegetables create more alkalinity in the body and the urine, further reducing the acid load.
  1. Take magnesium-potassium citrate. To boost citrate—and reduce the risk of kidney stones—you can supplement with a combination of potassium citrate and magnesium citrate. High doses of both are preferable to potassium supplementation alone and lowered the rate of calcium oxalate kidney stone recurrence from 64% to 13% in one study.
    Other trials have also shown that potassium and magnesium citrate supplementation reduces kidney stone recurrences. The combination lowers stone risk factors by alkalinizing the urine, decreasing calcium excretion, and enriching the urine with magnesium, another inhibitor of calcium-containing stones. The total dose of potassium citrate should provide 1,600 mg of elemental potassium and the dose of magnesium citrate should provide 500 mg of elemental magnesium per day, in divided doses.



Some helpful navigation on kidney structure and kidney stone point of origin.

Additional Tips

  • Get enough antioxidants. There is a growing body of evidence that increasing anti­oxidant intake can help reduce your risk of stones. In one preliminary human study, 1,000 mg per day of pomegranate polyphenol extract in people with recurrent kidney stones lowered the concentration of calcium oxalate in the urine. You can take supplements or eat a variety of antioxidant-rich foods. (Think bright, colorful fruits and vegetables.)
  • Take probiotics. There is evidence that kidney stones are related to certain gut microbes and preliminary studies show that probiotics, such as bifido­bacterium (B. animalis subsp. lactis), can help reduce the risk of stones. You’ll find probiotics in plain, low-sugar yoghurt.
  • Manage your weight. Being overweight and having insulin resistance significantly increases the risk of kidney stones. If you are overweight and/or have diabetes, pre-diabetes, or metabolic syndrome, returning to a healthy weight, improving your blood sugar control (improving insulin sensitivity), and getting more physical activity can greatly lower your risk.