Understanding kidney stones
Kidney stones, also known as renal calculi, are hard mineral and salt deposits that form in the kidneys. They can vary in size, ranging from tiny grains to larger stones that can cause severe pain as they pass through the urinary tract (1). Kidney stones are a common urological condition and can affect people of all ages, although they are more prevalent in adults, particularly between the ages of 30 and 60.
Kidney stones are a common condition worldwide. According to estimates from the National Health Service (NHS) in England, kidney stones affect about 10–15% of the population at some point in their lives (2). The prevalence appears to be increasing in recent years, possibly due to changes in dietary habits and lifestyle factors (2,3).
How do kidney stones work?
The pathophysiology of kidney stones involves the formation of solid masses within the urinary tract, typically in the kidneys, ureters, bladder, or urethra. Kidney stones can vary in size, composition, and location, and their formation is influenced by a variety of factors (1).
Kidney stones form when the concentration of certain substances in the urine exceeds their solubility limit, leading to supersaturation. Common substances that can form kidney stones include calcium, oxalate, uric acid, and cystine (1). Factors such as dehydration, diet, medications, and underlying medical conditions can contribute to urine supersaturation (4).
Once urine becomes supersaturated, crystals of various substances may form and aggregate to form small particles or “nuclei.” These nuclei serve as the foundation for the development of kidney stones. Over time, the nuclei can grow in size as additional crystals deposit onto their surface. As crystals continue to grow, they may aggregate and adhere to each other, forming larger aggregates. These aggregates can eventually coalesce into solid kidney stones. The specific composition of the stones depends on the types of substances present in the urine (1).
Stones that form in the kidneys may remain within the kidney’s collecting system, where they can grow further or become lodged in the renal pelvis or calyces. Factors such as urinary stasis, anatomical abnormalities, or ureteral obstruction can contribute to stone retention. As kidney stones grow or move within the urinary tract, they can cause obstruction of the urinary flow (5). Obstruction can lead to urinary stasis, increased pressure within the urinary system, and stretching of the renal capsule, resulting in renal colic—severe flank pain that radiates to the groin or lower abdomen. Prolonged obstruction or irritation of the urinary tract by kidney stones can lead to inflammation and tissue damage (5). In some cases, stones may become coated with bacteria and contribute to urinary tract infections (UTIs) (6).
Understanding the root causes
The main factors contributing to the formation of kidney stones include dehydration, dietary factors and some medical conditions (4).
Dehydration is an important one, as insufficient fluid intake can lead to concentrated urine, increasing the risk of stone formation. Low urine volume reduces the ability of the kidneys to dissolve minerals, making it more likely for crystals to form and aggregate into stones (4).
Food can also be a contributing factor. Food high in oxalate, a high sodium diet and a low calcium diet can precipitate stone formation (4). High oxalate foods can increase the risk of calcium oxalate kidney stones. Sodium intake can also increase urinary calcium excretion, contributing to the formation of calcium-containing kidney stones (7). A diet high in animal protein, particularly red meat, can increase uric acid production and contribute to uric acid stone formation. There is conflicting evidence as to whether a diet low in calcium may increase or decrease the risk of kidney stones, as it has been proposed that low dietary calcium can increase the absorption of oxalates in the intestines (7).
Medical conditions that can increase the likelihood of kidney stone formation are hypercalciuria (excessive urinary calcium excretion), hyperoxaluria (elevated levels of oxalate in the urine), cystinuria (an inherited disorder resulting in excessive cystine excretion), gout and UTIs (4). Some bacteria in UTIs can produce urease, an enzyme that breaks down urea into ammonia, leading to alkaline urine and increased risk of struvite stone formation (8).
Some medications can also increase the risk of kidney stones, including diuretics, calcium-based antacids, certain antibiotics (e.g., sulfonamides), and protease inhibitors used in HIV treatment (4).
Other factors include a family history of kidney stones and obesity, as it is associated with metabolic changes that can increase the risk of kidney stones, including insulin resistance, hypercalciuria, and low urinary citrate levels (4, 9).
Signs and symptoms
Lower back pain is usually the most common symptom. The pain can be sudden and severe, typically located in the back or side, and may radiate to the lower abdomen or groin area. The pain can come in waves and fluctuate in intensity. The discomfort from a kidney stone typically arises from irritation or obstruction, escalating quickly to intense pain. While kidney stones often pass without causing harm, they commonly come with significant discomfort (1, 10).
Haematuria, or blood in the urine, can occur due to irritation of the urinary tract by the passing stone. The urine may appear pink, red, or brownish in colour (10).
Individuals with kidney stones may feel a frequent urge to urinate, and urination may be painful or accompanied by a burning sensation (10).
Some people may experience nausea and vomiting, especially if the pain is severe. In cases where there is an associated UTI or kidney infection (pyelonephritis), fever and chills may develop. The presence of bacteria or pus in the urine due to an infection can cause it to appear cloudy or have a foul odour. Kidney stones can sometimes block the flow of urine, leading to difficulty in passing urine or a decreased urine output (1, 10).
Herbal solutions
The herbal approach to managing kidney stones involves a synergistic blend of medicinal plants that have a wide spectrum of properties (11). The key actions that are needed to help with easing pain, and managing with the passage or dissolution of stones are the following:
- Antilithic, helping to prevent the formation of stones or gradually dissolve stones
- Antispasmodic and smooth muscle relaxant
- Diuretic
- Antibacterial
- Demulcent
In herbal medicine, plants with antilithic properties are those considered to help prevent the formation of stones or that help gradually dissolve stones.
One of the main medicinal plants that can help dissolve and remove urinary gravel, with extensive case reports of its effectiveness is Goldenrod (Solidago virgaurea) (12). Its mechanism of action is not clearly understood, but it seems to help remove urinary gravel as well as increase diuresis in people with kidney stones (13). It is therefore also considered a diuretic, and it has been traditionally used for urinary retention (12).
Gravel root (Eupatorium purpureum) has also been traditionally used to help dissolve kidney stones. It contains volatile oils, flavonoids, resins as well as potassium chloride, silica, calcium, sodium, acid phosphate and some pyrrolizidine alkaloids (PAs)(14). Because of these potentially hepatotoxic PAs, continuous long-term use is not recommended, due to hepatotoxicity risk. It should also be avoided in people with liver disease (15).
The herb varuna (Crateava nurvala) has been used in the Ayurvedic tradition for the management of urinary stones (16). In experimental models it has shown significant inhibition of bladder stone formation, and in uncontrolled human studies it has been shown to aid the passage of stones as well as help with symptomatic control (16, 17).
Horsetail (Equisetum arvense) has a long history of traditional use as an antilithic and diuretic, aiding in the elimination of excess fluid from the body by improving urine production (11). A study specifically investigated the efficacy of horsetail in individuals with a history of uric acid kidney stones (18). Encouragingly, the results revealed that those who consumed horsetail experienced a notable increase in diuresis, indicating its effectiveness in increasing urine output. Another study showed its potential as an antilithic, as the group treated with a formulation containing predominantly horsetail had significantly lower calcium oxalate crystals deposits amount when compared with the placebo-only treated group. These findings emphasise the potential of horsetail as a remedy for managing uric acid and calcium oxalate kidney stones (19).
There is an interesting study supporting the use of black cumin (Nigella sativa) demonstrating significant antilithic properties. The use of 1g a day of black cumin for 10 weeks helped to significantly eliminate or reduce the size of small kidney stones when compared to placebo (20).
Examples of antispasmodic and smooth muscle relaxants that can help ease pain and the passage of small stones or gravel include cramp bark (Viburnum spp.) and wild yam (Dioscorea villosa). These can be helpful in the management of kidney stones when used in conjunction with herbs that have antilithic and diuretic actions.
Diuretics are an important aspect of the herbal strategy. They can increase urine output and promote the flushing out of substances that contribute to stone formation (11). These herbs work by stimulating the kidneys to produce more urine, which helps to dilute the concentration of stone-forming substances like calcium, oxalate, and uric acid in the urinary tract. Increased urine flow can also facilitate the passage of small stones and prevent the aggregation of mineral deposits. Examples of these herbs are dandelion leaf (Taraxacum officinale), cleavers (Galium aparine), celery seed (Apium graveolens), parsley (Petroselinum crispum) and juniper (Juniperus communis) (21).
Infection can provide a focus for stone formation, and stones can contribute to infection (6). Therefore, the use of anti-infective and anti-bacterial herbs may be relevant. This includes antibacterial herbs like echinacea root (Echinacea spp.), buchu (Agathosma betulina) and cranberry (Vaccinium spp.). It is important to consider that there is some clinical evidence to suggest that cranberry may slightly increase the risk of oxalate stone formation, due to the high oxalate content of cranberry (22).
Demulcent herbs to relieve inflammation and irritation in the kidney, urethra or bladder are also important. Examples of herbs that can be useful to manage kidney stones are marshmallow (Althaea officinalis) and couch grass (Elymus repens). Couch grass is not only a demulcent but also inhibits the growth of microorganisms and has a diuretic action (11).
Holistic solutions
Conventional medical treatment can aid with the passage of stones, and minimally invasive surgery can break down bigger stones. However, there is an important role for diet, lifestyle choice and the use of herbs to help prevent stone formation and/or assist in the dissolution and passage of smaller stones (23).
Adequate hydration is crucial for preventing kidney stone formation. Drinking plenty of water helps to dilute urine and prevent the concentration of stone-forming substances (4). Aiming to drink at least 8–10 glasses of water per day is recommended. Sweetened and carbonated drinks have been associated with an increased risk of developing kidney stones in several studies (24). One study reported a 23% increased risk in kidney stone formation in people drinking one carbonated drink a day (25).
Certain dietary modifications can also help reduce the risk of kidney stone formation. These are valuable in people who already have an increased risk of developing them. Limiting intake of foods high in oxalate is recommended, for example spinach, rhubarb, nuts, and chocolate. Moderating the consumption of foods high in purines, such as red meat, organ meats, and shellfish, is advisable to prevent uric acid stone formation. High coffee intake has also been associated with an increased risk of developing kidney stones (4). On the other hand, increasing the intake of citrate-rich foods like lemons, oranges, and melons can help inhibit stone formation (23).
Lifestyle choices can also have an impact. Engaging in physical activity can help maintain a healthy weight and therefore reduce the risk of obesity-related kidney stones. Chronic stress can also contribute to kidney stone formation, so stress management techniques that work for the individual are beneficial (26). Both smoking and heavy alcohol intake can impair kidney function and increase the risk of kidney stones, so it is advised to avoid tobacco and excessive alcohol consumption (27).
References
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- Littlejohns TJ, Neal NL, Bradbury KE, Heers H, Allen NE, Turney BW. Fluid intake and dietary factors and the risk of incident kidney stones in UK Biobank: a population-based prospective cohort study. Eur Urol Focus. 2020 Jul;6(4):752-61.
- Turney BW, Appleby PN, Reynard JM, Noble JG, Key TJ, Allen NE. Diet and risk of kidney stones in the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition (EPIC). Eur J Epidemiol. 2014 May;29:363-9.
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- Ardakani Movaghati MR, Yousefi M, Saghebi SA, Sadeghi Vazin M, Iraji A, Mosavat SH. Efficacy of black seed (Nigella sativa L.) on kidney stone dissolution: A randomized, double‐blind, placebo‐controlled, clinical trial. Phytother Res. 2019 May;33(5):1404-12.
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- McHarg T, Rodgers A, Charlton K. Influence of cranberry juice on the urinary risk factors for calcium oxalate kidney stone formation. BJU Int. 2003 Nov;92(7):765-8.
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