The majority of the kidney stones found are made up of calcium oxalate. These are formed when the pH of urine is acidic, and the calcium oxalate crystallizes from urine. The patient is advised to stay away from the foods containing oxalate such as beet, soy products, spinach, sweet potato, nuts, and black pepper. However, there are some arguments for and against regarding the use of calcium supplements and dietary calcium in the patients with kidney stones.
Role of Oxalate in Kidney Stones
The calcium concentration in the milk is high and further they have a very good bioavailability i.e. the calcium from the milk is efficiently absorbed by the body. As most of the kidney stones formed are made up of calcium and oxalate, theoretically it seems rationale to avoid both these things in the diet of the people who are at risk of developing kidney stones. But the practical studies conclude otherwise. There are two types of calcium available to the body, one is dietary and the other is through nutritional supplement such as pills. The rate limiting factor of the formation of the kidney stones is the presence of oxalate with high concentration. If the calcium concentration is high, it may be used by the bones or can be excreted by kidneys in the form of a soluble salt. But high concentration of oxalate may result in to a crystallized form that leads to kidney stones.
Is Milk Good for Kidney Stones?
Does drinking milk in people with kidney stones helps? Milk contains a good amount of calcium. 100 grams of milk contains approximately 120 mg of calcium. It is good for bones and manages the symptoms of people suffering from osteoporosis. Further, it also helps in muscle movements. The absence of calcium may reduce the capacity of body in blood clotting. Thus, it is not advised to avoid calcium from the diet. However, it is believed that the intake of calcium in the patients with formation of kidney stones may aggravate the condition. But it is not true so far as dietary calcium is concerned. One of the established and independent risk factors for the formation of stones is lower dietary calcium. In a recently conducted study, it was found that the people with higher dietary calcium have lesser risk of developing stones as compared to the people with low calcium in their diet. The studies propose following mechanism of actions to support their stand:
- Reduction in Oxalate Absorption: The dietary calcium efficiently binds with the oxalate present in the diet and does not allow the dietary oxalate to be absorbed in the body. Thus, there is a reduction in the overall concentration of oxalate in blood and lesser risk of stone formation.
- Importance in Kidney Stones: The urinary oxalate is more critical in the formation of kidney stones as compared to urinary calcium.
However, it was not the case when calcium supplement is taken. In a study, it was found that when people took dietary calcium the chances of formation of kidney stones reduced while the chances increase when calcium supplement is taken. Although the reason to this effect is yet to be known, but it is believed that there are certain other factors associated with dietary and dairy calcium that reduces the risk of stone formation.
Two types of calcium supplement exist in the market. The dietary supplements such as milk and cheese and the calcium supplement in the form of pills. The calcium supplement does not increase the risk of stone formation. It is found that calcium in the dairy products, in fact reduces the chances of kidney stone formation and calcium pills tend to increase it. Further, it is not advised to remove calcium from the diet as it has many more roles in the body. The best way is to drink sufficient quantity of water and avoid foods rich in oxalate.
- Curhan, Gary C., et al. “Comparison of dietary calcium with supplemental calcium and other nutrients as factors affecting the risk for kidney stones in women.” Annals of Internal Medicine 126.7 (1997): 497-504.
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