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Risk Factors of Kidney Stones

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Based on a report
[1], it has found that kidney stone incidences have increased in the United States between 1980 and 1994. It also predicts that, within the United States, about 10–15% of adults will be diagnosed with a kidney stone.

Diet plays an important role in the development of kidney stones. As we eat richer diets, we must deal with more wastes. And wastes come through our kidneys and out in our urine. The relation between diet and kidney stones may be different in older adults because the metabolism of many dietary factors, such as calcium, may change with age. Body size also affect the relation between diet and kidney stone formation. Therefore, dietary recommendations for stone prevention should be tailored to the individual patient [2].

Four Major Dietary Factors

There are four major "hot spots" in a stone former's diet:
  1. protein
  2. calcium
  3. oxalate
  4. salt
All can directly influence our potential for developing kidney stones and they can interact with one another to tip the balance toward stone formation.

24-hour Urine Study

A simple examination of urine component can reveal a patient's stone risk. It has been found that:

  • higher calcium => higher stone risk
  • higher oxalate => higher stone risk
  • higher urate => higher stone risk
  • higher urine volume => lower stone risk
  • higher citrate => lower stone risk
    • Citrate is natural inhibitor of kidney stones.
    • The vast majority of citrate is made right in kidney and controlled by urinary pH. The kidney makes more citrate if urinary pH is high (alkaline) and less if it is low (acidic).
    • More recent studies have suggested that citrus fruits may reduce stone risk slightly by raising urinary citrate. However, citrus peel is high in oxalate.
    • To treat stone formers, doctors usually prescribe alkaline potassium salts (including potassium citrate and potassium bicarbonate). Potassium citrate compounds are somewhat better than potassium bicarbonate compounds because they raise the urinary citrate level more.

Risk Factors

In the following table, all risk factors of kidney stones are described in details [1-5]:


Risk Factors

Descriptions

Calcium

  • Calcium stone formers generally have a high urinary calcium.
  • Calcium is the most abundant mineral in kidney stones.
  • More calcium is absorbed from the upper intestine while more oxalate is available in the lower intestine.
  • Reducing urine calcium should be a goal for stone formers, but not via dietary restriction.
  • A 5-year randomized clinical trial of men with a history of calcium oxalate stones found that a normal calcium, decreased sodium, and decreased animal protein diet was more effective for reducing stone events than was a restricted calcium diet (Borghi et al., 2002).
  • Clearly, strong research evidence now supports adequate calcium intake for patients who form kidney stones. Low-fat dairy products, green leafy vegetables, broccoli, fortified foods, and almonds are excellent sources.
  • Patients should avoid calcium supplements in favor of calcium-rich foods (see [12]; the new research has associated calcium supplements with an increased kidney stone risk).
  • Low-calcium diet is bad for two reasons:
    • Lower bone density
      • If you are on a low-calcium diet, your bone problem is going to get worse, particularly as you grow older.
      • There is growing evidence to indicate that stone formers as a group have lower bone densities than the general population.
    • Higher urinary oxalate

      • Calcium and oxalate bind in the gut and in the urine to form a nonabsorbable compound. Low dietary calcium permits greater free oxalate to be absorbed in the gut and excreted in the urine, which may be counterproductive for calcium oxalate stone formers.
      • Ordinarily, there is an excess of calcium over oxalate in the first part of your intestine. Since calcium and oxalate combine easily, most of the oxalate in your diet unites with calcium in the upper intestine. In essence, tiny calcium oxalate stones form inside your bowl. Since the intestine is so wide, these tiny stones make no differences. There is, however, very little oxalate available as your food moves to the last part of the intestine, the colon. And it is in the colon that most oxalate is absorbed by the body.
      • In other words, with ordinary bowel function, only a very small part of the ingested oxalate is absorbed because most of it combines with calcium in the first part of the intestine.
      • In a recent study, men over 40 on low-calcium diets made more stones than men on medium-calcium diets. The increased oxalate absorption may have been a factor.
Oxalate

Oxalate is a component, with calcium, of the majority of kidney stones. Oxalate is present in more than 75% of all stones.  What most people with kidney stones don't know is that oxalic acid, like calcium, performs a vital function.  98 % of the oxalic acid in the body is produced internally and is used for moving food through the digestive tract by peristalsis.  Oxalic acid also aids in the absorption of calcium into the cells[7].

Based on [7], leftover oxalic acid, along with excess calcium, is removed from the blood by the kidneys and passes into the urine.  Calcium oxalate permeates the urine generally, but only in those people whose urine is overloaded with acid waste does it form stones.  [7] also says that eating greens high in oxalates in moderate amount should be OK if they are raw.
  • Calcium oxalate is a very insoluble salt.
  • Though only 10% to 20% of urinary oxalates come from dietary sources (Morton, Iliescu, & Wilson, 2002), dietary reduction is commonly advised for calcium oxalate stone formers.
  • It has been suggested that because there is much less oxalate in the urine than calcium in the urine, urinary oxalate concentration is much more critical to the formation of calcium oxalate crystals than is the urinary calcium concentration; reducing urine oxalates may have a more powerful effect on stone formation than can reduction of urine calcium (Morton et al., 2002).

  • Oxalate is found only in plant foods, and the highest concentration are in dark green, leafy vegetables such as spinach, and in rhubarb, chocolate, tea, okra, nuts, beans, beets, wheat bran, and strawberries. A thorough oxalate list can be found on the Web site of the Oxalosis and Hyperoxaluria Foundation (http://www.ohf.org/diet.html). For a simple list of high-oxalate foods, visit http://www.gicare.com/pated/edtgs29.htm.

  • Because it binds vital nutrients such as calcium, long-term consumption of foods high in oxalic acid can be problematic. Healthy individuals can safely consume such foods in moderation, but those with kidney disorders, gout, rheumatoid arthritis, or certain forms of chronic vulvar pain (vulvodynia) are typically advised to avoid foods high in oxalic acid or oxalates.
  • There are four sources of the oxalate that appears in the urine.

    • large amount of protein

    • excess amounts of vitamin C

      • Excess amounts of vitamin C can be excreted in the urine as oxalate.

      • Vitamin C is an acid (ascorbic acid). It tends to lower urinary pH, which in turn lowers urinary citrate, a natural inhibitor of kidney stones.

      • Recent data suggest that even small amounts of vitamin C supplements-doses of 250 mg to 500 mg-can raise urinary oxalate in some patients.

    • waste products of general metabolism

    • seven foods that greatly enhance urinary oxalate excretion:
      • spinach
        • In various food tests, spinach seems to produce the greatest rise in urinary oxalate.

      • rhubarb
      • beets
      • nuts
      • chocolate
      • tea
        • One patient who started to keep a large pitcher of iced tea on his desk at work. He was consuming 4 to 6 large glasses a day. He formed his first stone 2 months later.
        • For those with excessive urinary oxalates, black and iced tea should be eliminated because both teas are high-oxalate beverages [5&8].
      • wheat bran


  • However, the "bioavailability" of the oxalate may be different in various foods.

    • In other words, some oxalate-containing foods are more problematic than others.
    • Each person absorbs and excretes various dietary elements differently.

  • The problem with oxalate recommendations

    • Oxalate is difficulty to measure in both food and body fluids.
    • The oxalate content of food can vary greatly from one batch of a given food to another.

      • It is believed that aging increases the amount of oxalate in plants.
      • Although oxalate has no known function in animals, it is believed to help plants dispose of calcium. Animals have kidneys that excrete excess calcium. Plants do not. The theory is that the oxalate binds to the excess calcium, trapping it in the leaves, bark, and skin. As older leaves are shed, the plant disposes of unwanted calcium. As the plant gets older, the oxalate content tends to increase.
    • The bioavailability of oxalate differs in foods.

      • Strawberries and spinach are both high-oxalate foods. However, the oxalate in spinach is more bioavailable than it is in strawberries.
      • If oxalate is present as oxalic acid (the form found in younger plants), it is more bioavailable. If it is present in food as a calcium oxalate salt (the form found in older plants), it is less bioavailable in the intestines, and absorption decreases.

  • Key issues in oxalate control (note that reduction of high oxalate foods is the goal for typical stone formers rather than strict avoidance of all oxalate-containing foods which would be very difficult):
    • control portion size

    • control fat intake
      • In people prone to the overabsorption of oxalate, a high-fat diet will cause more oxalate to be absorbed.

    • avoid vitamin c supplements

      • Dr. Rodman advises his stone-forming patients not to take vitamin C supplements beyond what is in a balanced diet.

    • watch for hidden oxalates

      • the peanut oil used to cook in most Chinese food.
    • drink two large glasses of water-or more when you know you have overindulged.


High Blood Uric Acid (See Also High Animal Protein Intake)


  • Saturation levels of uric acid in blood may result in uric acid stones.
  • There is no inhibitor of uric acid crystal formation (Menon & Resnick, 2002), so dietary measures focus on reducing uric acid and increasing urine volume.
  • Some patients with gout eventually get uric kidney stones.
Acid Urine


  • If the urine is acid most of all of the time, you are at risk for making uric acid stones.
  • An acid urine also decreases citrate formation (the natural inhibitor of stones) by the kidneys, making a calcium oxalate stone more likely.
  • Normal urinary pH levels range between 5.0 and a little over 8.0. This varies with the time of day, food consumption, age, and other factors.

Lack of Fluids (or Dehydration)

 

  • Less urinary flow (due to less fluid intake) increases the relative frequency of stone formation.
  • Addressing fluid intake is the only therapeutic recommendation needed for some female stone formers. It is also one of the most important aspects of treating urinary tract infections in women.
  • Dilution of urine is necessary "24/7," or all day, every day.
  • Patients must accept the necessity of getting up at least twice at night to urinate, and should consume more water each time they rise to void [5].
  • What fluids to drink? For stone formers, you should drink more water and avoid excess caffeine, black tea, and grapefruit and apple juices. Lemonade is often recommended, as it supplies dietary citrate, a stone inhibitor and pH buffer when excreted later in the urine. [5].
High Animal Protein Intake

  • After low urinary volume, a high animal protein intake is the most important factor influencing the frequency of kidney stone disease.
  • The effect of excess animal protein (purine=>uric acid) is most obvious for the uric acid stone former.
  • High dietary protein is associated with increased urinary calcium. Thus, there is a link between meat consumption and both uric acid and calcium stone formation.
  • Too much protein can cause dehydration, which is a cause of kidney stones[6]
    • For every 50 grams of protein digested, your body must contribute 3 cups of water to dilute the resulting uric acid that is excreted.
    • In comparison, metabolizing an equal amount of fat or carbohydrates consumes less than 1/2 cup of water.
  • A study of 18 hypercalciuric stone formers found that a 15-day protein restriction had many positive effects on urinary markers of stone risk. Namely, significant decreases were seen in urine calcium, urine uric acid, urine phosphate, and urine oxalate. And, for unclear reasons, a beneficial increase in urinary citrate was observed (Giannini et al., 1999).
  • Diets high in animal protein will increase the chance of forming both uric acid and calcium oxalate stones for 3 related but slightly different reasons:

    • Animal protein contains high purines, whose end product is uric acid. More uric acid in the urine means that you are more likely to make a uric acid stone. In addition, one form of uric acid, urate, can act as a seed for calcium oxalate stones.

    • The excessive consumption of animal protein will lower the pH of urine, making it more acid. This lower urinary pH makes uric acid less soluble and thereby favors the formation of uric acid stones. It also suppresses citrate formation by the kidney, which reduces one the body's natural inhibitors of calcium oxalate formation.

    • One of the amino acids in all proteins, glycine, is metabolized to oxalate. Another amino acid, methionine, drives out more calcium in the urine. A diet higher in protein will therefore increase urinary calcium even though the amount of calcium in the diet remains constant.
Alcohol

By itself, alcohol does not contribute to stone formation. However, it does have two effects that may set the stage for stone formation.
  1. alcohol makes you pass more urine and can lead to dehydration.
  2. alcohol indirectly inhibits the ability of the kidneys to excrete uric acid.
Sodium
By itself, the sodium in your diet has only a minimal effect on the tendency of the urine to make stones. However, an increase in dietary sodium increases the urinary calcium.
Late dinner

  • Late-night eating is conducive to the formation of kidney stones.
  • The tendency of more families to follow late eating habit in the 1980s and 1990s may be one reason for the rising incidence of stone disease.
NSAIDs and Acetaminophen Taken in large quantities over long periods of time (no longer than 10 days, Dr. Oz  has warned), analgesics such as NSAIDs and acetaminophen can cause damage to the papillae of the kidney. Injured papillae can seed a stone as well as complicate the stone-forming process.
Diamox or Acetazolamide Some people with glaucoma form kidney stones while they are on carbonic anhydrase inhibitors (e.g., Diamox or acetazolamide) to lower eye pressure.
  • These medicines can lower urinary citrate and increase urinary calcium.
  • Patients can take potassium citrate supplements under doctor's supervision while the acetazolamide is continued, to minimize the tendency to make stones.


Rapid Weight Loss Rapid weight loss is as bad as, or potentially worse than, overeating protein when it comes to causing stone disease.

  • Doctors frequently give potassium bicarbonate and potassium citrate supplements to stone formers who are beginning a weight loss diet.

  • The best way to lose weight is to combine a nutritionally balanced diet with exercise and behavior modifications.
Hot Climates

Kidney stones often occur in people who move to hot, dry climates and in people whose work or exercise causes them to perspire heavily.
Fat Malabsorption
Fat malabsorption can lead to an increased net oxalate absorption and, finally, to increased urinary oxalate.
Problems with Voiding
Problems with voiding make bladder stones more likely.
  • The most common cause of bladder outflow problems is enlargement of the prostate gland in the older male.

Pregnancy
Pregnancy can increase stone risk due to the following factors:
  • Her diminished bladder capacity

    • As the fetus grows, there is less room in the pelvis for a full bladder.
  • The pregnant woman has to provide enough calcium in her blood to form a whole new skeleton. Urinary calcium will rise to its highest levels in the last trimester. Therefore, stone formation can result from this low urine flow and high urinary calcium.

Genetic Predisposition
If one or both of your parents made stones, there is a greater chance that you will make stones.
Men vs. Women


Stone disease is much more common in men than in women because of the following factors:
  • Men generally have a larger muscle mass than women. Hence they have more of the daily breakdown and rebuilding of tissue that results in metabolic waste. And an increase in metabolic waste predispose people to stone formation.

  • Men generally eat more meat than women do.

  • The male urinary tract is more complicated than the female urinary tract.


Warning

This article is not intended as and does not substitute for doctor's advices - the content presented is for your information only. Please see your personal physician for further evaluation of your individual case.

Reference(s)

  1. Stamatelou, Kiriaki K.; Francis, Mildred E.; Jones, Camille A; Nyberg Jr., Leroy M.; Curhan, Gary C. (2003). "Time trends in reported prevalence of kidney stones in the United States: 1976–1994"
  2. Taylor EN; Stampfer MJ; Curhan GC (2004). "Dietary factors and the risk of incident kidney stones in men: new insights after 14 years of follow-up."
  3. No More Kidney Stones by John S. Rodman, M.D., R. Ernest Sosa, M.D., and Cynthia Seidman, M.S., R.D, with Rory Jones.
  4. The Complete Idiot's Guide to Detoxing Your Body by Delia Quigley.
  5. The Role of Diet in the Prevention of Common Kidney Stones: Dietary Changes to Prevent and Reduce Stone Formation
  6. The Swiss Screte to Optimal Health by Thomas Rau, M.D. with Susan Whler
  7. The Acid Alkaline Balance Diet by Felicia Drury Kliment
  8. Iced Tea Can Contribute to Painful Kidney Stones
  9. Acid-Alkaline Balance
  10. Building Strong Bones
  11. Types of Kidney Stones
  12. 6 Health Risks of Calcium Supplements
  13. A Diet to Prevent Kidney Stones: Foods Vary
    • Low-sodium diet is healthy for the kidneys as well as the heart.
    • People can also reduce their risk of developing kidney stones and improve their health in general by increasing their intake of melons and citrus fruits like lemons, limes and oranges, says Dr. Monga.
  14. 9 Unknown Signs You’ll Get Kidney Stones and How to Prevent Them
  15. Alpha-lipoic acid prevents kidney stones in mouse model of rare genetic disease
  16. How Not to Die from Kidney Disease | NutritionFacts.org

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