A Poser: Can Excessive Intake of Vitamin C Cause Kidney Damage?

 

 A Structural Engineer friend of mine asked me very early  predawn  morning even before the sun could rise yesterday whether high doses of vitamin C can damage   

the  kidneys?

Frankly, I wanted to post my much more interesting article yesterday on:

 

  “We are Only on Transit here in This World to The Next World”

 

This article I wrote 3 weeks ago  has been in the queue waiting for posting ever since. I wanted to get that out first. But since  you ask me this question on vitamin  C and nutrition, I have given  my priority for your sake. After this  I need to publish my thoughts on that more interesting question.

 

Following that,  I shall then  write a few articles on health, drugs, and on medicine that are also my areas of specialization, including  Part 2 of this article on vitamin C, its effect when taken in excess and compare it with fat-soluble vitamins like retinol (vitamin A). I believe more people, especially readers would be more interested if I should write on health, nutrition and medicine that may affect them directly, rather than me writing  on spiritual entities they cannot see or understand that are mysteries beyond them - but not for me with God Guidance to "see"  

 

Thank you, Engineer CK Cheong, for bringing up this excellent question! The relationship between high doses of vitamin C and kidney damage is indeed an area that has been studied, albeit with some mixed findings. Let me address your query systematically.

 

Vitamin C and Kidney Damage:

Vitamin C (ascorbic acid) is a water-soluble vitamin, and excess amounts are typically excreted in the urine. However, taking very high doses (above the tolerable upper intake level of 2,000 mg/day for adults) can lead to potential complications. These are:

 The formation of oxalate and kidney stones. High doses of vitamin C are metabolized into oxalate, which can combine with calcium to form calcium oxalate crystals—the most common component of kidney stones. Some studies suggest that excessive vitamin C supplementation increases urinary oxalate excretion, thereby raising the risk of kidney stone formation in predisposed individuals, such as those with a history of nephrolithiasis.

A 2013 Swedish study found that men taking 1,000 mg or more of vitamin C per day had a higher risk of kidney stones compared to those not supplementing with vitamin C. This association wasn't observed in women.

However, I have to say this occurs rarely.  High doses of vitamin C may precipitate acute kidney injury (AKI) in individuals with pre-existing kidney disease. This is primarily due to hyperoxaluria (excess oxalate in the urine) or the precipitation of crystals in the renal tubules.

 Excessive calcium intake can also lead to kidney stones more than excessive vitamin C intake. High levels of urinary calcium (hypercalciuria) can combine with oxalate or phosphate to form kidney stones. In fact, recent studies suggest that dietary calcium intake actually protects against kidney stones by binding oxalate in the gastrointestinal tract, reducing oxalate absorption and excretion. But unfortunately, calcium supplements, especially when taken without food, may slightly increase the risk of kidney stones.

Safe Doses and Recommendations:

 For most healthy individuals, doses of vitamin C below 1,000 mg/day are considered safe. People prone to kidney stones or with pre-existing kidney issues should limit vitamin C supplementation and focus on dietary sources instead. To avoid kidney stones, calcium intake should ideally come from food rather than supplements, and sufficient hydration is crucial.

While vitamin C at high doses can contribute to kidney stone formation in certain individuals, the risk isn't universal. Excessive calcium intake also poses risks, particularly when taken as supplements. Ensuring balanced nutrition, drinking plenty of water, and avoiding excessive supplementation are key preventive measures.

But what is more damaging to the kidneys is not vitamin C in high doses, but  certain foods can have nephrotoxic effects (poisoning effects on the kidneys), particularly in individuals with pre-existing kidney conditions.

Since nutritional toxicology is one of my areas of expertise when I was working at the Massachusetts Institute of Technology (MIT) in the late 1960’s, let me explain in a simple way for ordinary lay-readers, an overview of starfruit, petai (stink bean), and other foods known to be potentially harmful to the kidneys

The first is  starfruit (Averrhoa carambola). This fruit contains a neurotoxin called caramboxin, as well as oxalates. The effect on kidneys is that the neurotoxin can accumulate in people with kidney disease and cause neurological symptoms like confusion, seizures, and even coma. It is also high in oxalate content. This  increases the risk of kidney stone formation, especially in predisposed individuals.

The second is petai (stink bean, bitter bean) very popular among the Malays who coincidentally also suffer from higher rates of kidney failures than the Chinese and Indians in Malaysia, besides their higher rates of diabetes can also cause kidney failures. The toxin in petai is djenkolic acid, a sulphur-containing amino acid.

The effect on kidneys is, djenkolic acid is poorly soluble and can crystallize in the kidneys or urinary tract, leading to djenkolism. Symptoms include abdominal pain, difficulty urinating, and acute kidney injury. It is particularly harmful in individuals with compromised kidney function.

There are also foods high in oxalates such as spinach, rhubarb, beets, nuts (like almonds), chocolate, and sweet potatoes.

The effect on kidneys is, oxalates can bind with calcium to form insoluble calcium oxalate crystals, a major component of kidney stones. Excessive intake increases the risk of kidney stone formation, particularly in susceptible individuals.

High-protein Foods (excessive consumption), examples like  red meat, poultry, eggs, and dairy products may also be harmful to the kidneys. The effect of high protein is, it increases the workload of the kidneys due to higher urea production during protein metabolism.

Thus, a high protein diet may accelerate kidney damage in individuals with chronic kidney disease (CKD). Then there are also processed foods with high sodium content such as chips, canned soups, processed meats. High sodium intake can lead to fluid retention, increased blood pressure, and strain on the kidneys. Over time, this contributes to CKD progression.

Besides high sodium, there are also foods high in potassium such as  bananas, oranges, avocados, tomatoes, potatoes. In individuals with CKD, the kidneys may struggle to excrete potassium effectively, leading to hyperkalaemia (high potassium levels), which can cause irregular heartbeats and cardiac arrest.

There are also artificial sweeteners in excess that can also damage the  kidneys, such as aspartame, saccharin, sucralose. Studies suggest chronic excessive intake of these artificial sweeteners  may affect kidney function, but evidence remains inconclusive. Moderation is key.

Consider also grapefruit and grapefruit juice. These contain toxins like furanocoumarins that interfere with enzymes like CYP3A4.

Its effect on kidneys is, this toxin may alter the metabolism of medications processed by the kidneys, potentially causing nephrotoxicity. It is particularly dangerous if combined with certain medications like statins or immunosuppressants.

Ah! You may be surprised that excess caffeine in coffee, tea and energy drinks  can also damage the kidneys. Excessive caffeine can increase calcium excretion in urine, promoting the formation of kidney stones. Chronic overuse may reduce kidney function over time.

Alcohol (ethanol)  and its metabolites are toxic too. Chronic alcohol consumption can lead to dehydration and impair kidney function. In severe cases, it may result in acute kidney injury.

 Cola drinks with high phosphoric acid content are toxic to the kidneys The phosphoric acid can lead to kidney stone formation and has been linked to decreased kidney function in long-term studies.

Certain  herbal supplements such as Aristolochia, St. John’s Wort, liquorice root can be toxic to the kidneys. Aristolochia contains aristolochic acid, which is directly nephrotoxic and carcinogenic. Liquorice root in excess can cause hypokalaemia and high blood pressure, damaging the kidneys.

 Foods high in purines, examples, organ meats, sardines, anchovies can be harmful.

Their effect on kidneys is that during the metabolism of purines it produces uric acid, which can crystallize and cause kidney stones or gout.

Foods  high in sugar contents, examples,  sweets, sugary drinks, pastries can have a deleterious effect on kidneys as excessive sugar intake can contribute to diabetes, a leading cause of CKD. Sugars may also promote obesity, indirectly straining the kidneys.

Last, but not least on my list is, unripe avocado leaves. The toxin present in these leaves and seeds too is persin.  This toxin can lead to kidney failure in animals and potentially in humans if consumed in large amounts.

My advice as a former research nutritionist, food scientist, analytical food quality controller,  and a clinician is, people with healthy kidneys can generally handle these foods in moderation, but those with compromised kidney function or at risk for kidney disease should consult a healthcare provider who specializes in nutrition or a dietitian for personalized dietary advice.

The key focus is on a balanced diet, rich in fruits and vegetables but low in excessive sodium, sugar, protein, and harmful toxins, is critical for kidney health.

Nutritional medicine and nutritional toxicology are  very complex subjects  should I explain further in greater depth and in technical details. So is toxicology in forensic science I studied at Cambridge for my postdoctoral  

Take care and enjoy your journey of learning with me dear CK Cheong. Your curiosity is truly a gift to yourself and others!