Almost all of us are familiar with the term kidney stones. The term is very popular and it indicates that the incidence of kidney stones in the community is so high. Several studies report that every year up to half a million people come to the emergency room because of kidney stones. In the United States, it is estimated that one in ten people will have a kidney stone at some point in their life and kidney stones are more common in males. In India, about 12% of people with kidney stones in total population are susceptible to urinary tract stones. Of this 12%, 50% of the population are severely affected by kidney injury, which can even lead to kidney loss. On average, the chances of any of us having at least one kidney stone in our lifetime is about 10%. In developing countries, including Indonesia, the occurrence of stones is increasingly frequent. It is apparent that the incidence of kidney stones is very common. However, there a the fact that many kidney stones are asymptomatic and found during medical check-ups for problems not related to kidney stones.

The high incidence of kidney stones cannot be separated from various underlying risk factors. This is why some people are more prone to developing kidney stones.” These risk factors at least include: genetics, age, dehydration, obesity and diet, as well as certain conditions.

Regarding genetic factors that cannot be modified, Hou stated that there are many genes that may play a role in the formation of kidney stones. The contribution of the polygenic influence of multiple loci has been investigated in genome-wide association studies and candidate gene studies, showing that a number of genes and molecular pathways contribute to stone formation risk, including transporters and channels; ions, protons and amino acids; calcium-sensing receptor signaling pathways; and metabolic pathways of vitamin D, oxalate, cysteine, purines, and uric acid (Howless and Thakker. 2020, Nat Rev Urol). By knowing the genetic factors in the formation of kidney stones, it is hoped that a better picture can be obtained about how certain people are prone to developing kidney stones. In addition to these advantages, there are other advantages, namely getting a more targeted treatment method, it is easy to determine a person's risk for the condition, which usually increases with age. Thus, prevention of kidney stones can be done earlier.

With regard to age risk factors, the people most likely to develop kidney stones are those between the ages of 40 and 60, although stones can appear at any age. Research shows that 35 to 50 percent of people who have one kidney stone will develop an additional stone, usually within 10 years of the first stone. Interestingly, age and gender have a strong influence on the type of rock formed. A study conducted at the Mayo Clinic, United States, showed that of the 43,545 samples of kidney stones received, calcium oxalate stones (67%) were the most common, followed by hydroxyapatite (16%), uric acid (8%), struvite ( 3%), brushite (0.9%), and cystine (0.35%). Men accounted for more stones (58%) than women. However, women experienced more stones than men between the ages of 10-19 (63%) and 20-29 (62%) years. Women experienced the most hydroxyapatite (65%) and struvite stones (65%), while men mostly experienced calcium oxalate stones (64%) and gout (72%). Although calcium oxalate stones are the most common type of stone overall, hydroxyapatite stones are the second most common before age 55, while uric acid stones are the second most common after age 55 (Lieske et al. 2014, Clin J Am Soc Nephrol) .

Regarding the risk factors for dehydration (lack of water in the body), dehydration facilitates the process of kidney stones forming and urinary tract infections, both of which can cause kidney damage if not treated quickly and appropriately.

Regarding obesity and diet, poor diet and what one eats are not only closely associated with obesity, but also with the incidence of kidney stones, an association that is well-documented. It should be noted that obesity itself, which is a marker for metabolic syndrome, is also associated with the risk of kidney stones. This means that poor diet intake can immediately give the opportunity for early formation of kidney stones or obesity conditions. It will be even worse if the two risk factors are mutually reinforcing. Of all the food intake, it is emphasized that the main cause is high salt (sodium) intake which will eventually cause an increase urinary calcium. Therefore, calcium stone is the dominant type among the various types of kidney stones, primarily the calcium oxalate stones which are more predominant compared to calcium phosphate stones. The dominance of calcium oxalate stones is because oxalate itself is either produced from the body, which is formed by the liver, or from outside the body through daily food intake. Examples of external sources of oxalate are certain fruits and vegetables (spinach, beets, carrots) and whole grains (nuts and chocolate), all of which are high in oxalate.

Regarding special conditions, such conditions are those that are able to facilitate the appearance of kidney stones, such as recurrent diarrhea. This condition results in a lack of body fluids, dehydration with a decreased amount of urine so that the urine becomes concentrated. Apart from diarrhea, there are also gout, high level of vitamin D, diuretic drugs, or receiving cancer treatment, which are not be discussed here.

Urine and its nature are the source of the onset of kidney stones. Urine in the urinary tract is too concentrated so that it tends to crystallize, and in contact with the walls of the urinary tract and the acidity of the urine. At one time, the walls of the urinary tract are lesioned, while the nature of the urine is also in a state of supersaturation. The lesion process will release damaged epithelial cells, or secrete mucus and/or pus, even erythrocytes, which in turn will become the core of the stone itself. In line with the passage of time, the formation of the stone core will be followed by the process of aggregation. Urine in such condition also contains a lot of salts (calcium, uric acid, cystine and other substances) and the presence of these insoluble salts is so large that it forms hard mineral deposits. In the next process, the nucleus continues to grow. The process of deposition around the nucleus in the urinary tract occurs in a longer time so that the stone continues to enlarge. In short, stones develop from a very small size, then enlarge with various sizes with a surface that can be sharp or dull. When the stone size is still between 4 mm and 6 mm, about 60 percent of the stones will pass on their own without medical intervention. The natural time for the stone to pass from the body is about 45 days. However, when the size is larger than 6 mm, most patients require medical treatment to help release the stone or even require surgical stone removal. This is because the stone is unlikely to pass spontaneously and is very likely to cause problems later on. The types of the formed stones include: calcium stones, uric acid stones, struvite stones, staghorn stones and cystine stones.

The common symptom of stones is kidney stone pain, also known as renal colic. This is one of the most severe types of pain, coming on suddenly. When a kidney stone moves from the kidney to the bladder, the opening of the duct is small. When a kidney stone dilates the opening of the urinary tract, severe pain occurs. Not a few people who have experienced kidney stones describe it by comparing it to the pain felt during giving birth to a baby or being stabbed with a knife. However, in fact most (80%) stones are easy to pass so they are asymptomatic. This means that we are all expected to be vigilant; no symptom does not mean no kidney stones.

The natural and common way to prevent kidney stones is to maintain adequate hydration, in addition to discipline with a balanced lifestyle. By drinking more water, the body always has sufficient hydration. This is the best way to prevent kidney stones. This condition is ideal to prevent crystals from sticking together, so that ultimately kidney stones are not easily formed. Drinking plenty of water is an important part of removing kidney stones and preventing new stones from forming. So, this method is very important. Staying hydrated is the key word. Furthermore, it depends on the type of kidney stone itself because each has its own peculiarities.

For example, calcium stones. In addition to the above precautions, it is recommended to eat less sodium. If the patient eats a lot of sodium, which is an ingredient in salt, this will increase the amount of calcium in the urine. After eating, the (excessive) oxalate "sticks" to the calcium in the kidneys. Therefore, it is recommended to eat less oxalate-rich foods and eat less animal protein, as well as avoid vitamin C supplements in those having or used to have kidney stones. A diet low in oxalate and calcium (from food), along with lower salt intake, and optimal hydration (target: 2 liters of volume excreted per day through urine) is expected to further prevent kidney stone formation. However, fruit and vegetable intake should still be maintained. Fruits and vegetables need to be chosen wisely so as not to consume foods high in oxalate. Reducing red meat intake can also be beneficial. But this all depends on the starting point and how much has been eaten. For practical implementation, avoid stone-forming foods such as beets, chocolate, spinach, rhubarb, tea, and most legumes because they are all rich in oxalates which can cause kidney stones. If one really wants those foods, then the way is to consume them in smaller amounts. In terms of caffeine intake, this has been shown to be associated with increased urinary calcium excretion and thus an increased risk of developing kidney stones, although in another report there was negative association between consumption of caffeinated beverages, such as coffee. Lemons contain citrate, which helps prevent calcium from building up and forming stones in the kidneys. As is well known, the citrate in juice binds to calcium, forming calcium citrate which is excreted before the calcium has had a chance to bind to the oxalate and form stones. A systematic review of 9 studies involving 541 people reported that low-calcium fluids may reduce the risk of kidney stones. Certain types of beverages, such as grapefruit, apple, and orange juice can reduce urinary calcium oxalate saturation, which in turn reduces stone formation (Gamage et al. 2020, Turk J Urol).

If a person has calcium oxalate stones, he should avoid the following foods to help reduce the amount of oxalate in the urine. Foods in question such as: nuts and its products, spinach and wheat bran. He is advised to consume calcium drinks such as milk, yogurt, some cheese and oxalate-rich foods together during meals. Oxalate and calcium from food are more likely to bind to each other in the stomach and intestines before entering the kidneys. This will reduce the chances of kidney stones forming.

By knowing that kidney problems are not simple, it would be wise if we all can apply discipline with a healthy lifestyle. Adequate rest, rest to eat before full, increase fiber rich and low salt diet, exercise regularly according to physical capacity, avoid counterproductive habits, avoid excessive stress, and, most importantly, all of that is supported by an elegant spirituality. Thus, we will be able to adapt in a life full of benefits, including avoiding kidney stones. Hopefully! []

Djoko Santoso
Professor, Faculty of Medicine, Universitas Airlangga
Chairman of Health Department, Indonesian Council of Ulama, East Java