HOW TRUE IS IT?

SPINACH AND MILK CAUSES KIDNEY STONE?

People believe thay eating spinach and drinking milk together can cause kidney stone formation in a long run. In theory, the combination of calcium from milk and the oxalic acid from spinach forms calcium oxalate crystals that will lead to blockage of urinary tract and formation of kidney stone.

How could this possibly be?

Spinach

Is a source of green leafy vegetable which is rich in beta carotene, 13 types of flavonoid and vitamin C, K, and magnesium. All this properties plays an important role in anti inflammatory such as asthma, osteoarthritis, osteoporosis, rheumatoid arthritis and gout. The most important element found in spinach is that it contain anti nutrient called oxalic acid that binds to calcium, preventing 95% of calcium absorption into the body. Oxalic acid is a dangerous poison at a high concentration thus when this oxalic acid is processed, it combines with other substances to form various salts, called oxalates. If this concentration is high enuogh in the body then it will precipitate out in crystalline form causing kidney and bladder stone in long run time.

Milk

Is one of the complete food in the world. It contain nutrients such as water, milk fat, protein, lactose, mineral(Ca, P, Mg, K, Na, Zn, Cl, Fe, Cu, sulfate, bicarbonate and citrate), vitamin (A, C, D, thiamine and riboflavin). The most important source of mineral that is found in milk is the calcium. Based on 1 liters of milk, it provide about 1100-1300mg of calcium. The purpose of calcium is for bone building and remodeling, muscle contraction, central nervous function and hormone secretion. However bone mass tends to get weak and porous when there is an inadequate supply of calcium. This is termed as osteoporosis which increase the risk of bone fracture in the hip, swine, swrist, ribs and pelvis. High intake of calcium in a short-term will produce constipation and increase the risk of kidney stones.


Where and how kidney stone is formed?

Kidney stones are formed from crystals in the urinary tract that separate from the urine and form a hard mass. If the crystals are large, they cause excruciating pain as it blocks the passage of urine, a burning sensation during urination and bloody urine. Kidney stone may form from combination of chemicals such as calcium combined with either oxalate or phosphate.

Crystals are formed in calcium oxalate which resulted in 70% occurrence.

Other than that, crystal formation is caused by :

-an increase of concentration above the supersaturation capacity of calcium or oxalic acid.

-a decrease in inhibitors concentration.

-genetic susceptibility.

IS THIS MYTH TRUE?

Based on the assumption above, the myth is not true. Although dietary oxalate plays a very important role in the formation of calcium oxalate stones, but taking high oxalic acid food together with high calcium food will actually decreases the risk of kidney stone formation. In a case study by (New England Journal of Medicine, 1993), it was concluded that high calcium intake is associated with a decreased risk of kidney stones. And in another case study, calcium restriction caused an increase in absorption and excretion of oxalate in the urine. As a result of the finding, calcium actually has a protective effect by binding to oxalate and phosphorus in the gut, preventing its absorption and lowering both urinary oxalate and urinary phosphorous that can contribute to the formation of kidney stones.

On the other hand, when calcium intake is low, more oxalate can be absorbed into the body, leading to higher urinary excretion of oxalates which binds to normal urinary calcium and precipitate to from kidney stones. When calcium intake is moderate to high, then some of it are being combined to oxalic acid and lost, while an adequate amount is still absorbed for the body.

References:

GlaxoSmithKline, 2009. Kidney Stones. Available from: http://www.calciuminfo.com/calciumquestions/kidneystones.aspx


Alexa P, 2008. Spinach. Available from: http://www.friedchillies.com/index.php/articles/detail/the-wonders-of-spinach/


Environmental Health & Safety, 2008. Available from: http://www.jtbaker.com/msds/englishhtml/o6044.htm


Richard Dion, 1997. Crystal Formation. Available from: http://www.agora.crosemont.qc.ca/urinesediments/doceng/doc_024.htm#Intéret