My vitamin C gummies. That's a lot of vitamin C, and I have 5 jars of these--I saved on shipping (my photo).
I begin this blog by stating vitamin C uptake and maintenance are so complex that no one should presume to self-treat. After doing much reading, I've come to the conclusion that individual absorption rates and physiological needs vary significantly. Monitoring of vitamin C status, by a qualified professional, particularly in someone with compromised health, is essential for optimal vitamin C status. Blood levels and health condition need to be evaluated and reevaluated, especially if a chronic underlying condition exists.
The question of vitamin C and kidney health arises in my home because my husband has one kidney. I love that kidney. I want to keep it healthy. Since he (and I) are looking at our next birthdays eclipsing another decade (we will be 80, if we make it), we must acknowledge that our kidneys are less efficient than they once were.
Kidney Position in the abdomen. Open Stax College. CC 3.0 license
One study, published in the BMJ Journal (previously known as the British Medical Journal) describes the gradual decline in kidney function that occurs as we age:
12 studies between 1958 and 2021 reported the decline rate of kidney function in healthy individuals: six prospective cohort studies, four retrospective cohort studies and two randomised controlled clinical trials, which included 129 359 healthy participants (range from 15 to 46 682) and ranged from 2 to 23 years duration. Annual decline rates ranged from −0.24 to −3.60 mL/min/1.73 m2/year (−0.37 to −1.07 in subjects without hypertension). Results were mixed as to whether decline rates sped up or slowed down with age, and whether decline rates differed between women and men, with studies showing conflicting results. This study was unable to determine the decline rates in different ethnicities.
Here is a great video that gives some good information about discovering current kidney health.
You can see from this report that no general statement about age-related kidney decline can be made except for this: kidney function does decline with age. That decline is highly variable. In adults with a kidney-compromising condition (such as high blood pressure) it is even less predictable.
Given the variability in kidney function it's obviously not valid to draw a conclusion about how vitamin C might affect an individual. Blood serum tests, taken over time, would be necessary to do that. However, we do have information about Vitamin C and kidneys. It would be wise to understand this general information so that we can seek the proper medical advice and evaluate that advice when we get it.
I'm a firm advocate for people taking a hand in the course of their medical care. No matter how much a doctor may care about a patient, the patient is certainly more invested in the outcome than the doctor.
I was prompted to write this blog by a question my daughter asked: How much vitamin C are we (her parents) taking? We had been ordering vitamin C gummies from Target for a while. The recommended dose on the bottle, for adults, is three gummies. My daughter said this is too much.
It turns out, three gummies have 282mg of vitamin C. In addition to the gummies, we take multivitamin gummies. Each serving of these gummies has 20 mg of Vitamin C. So, in total we were taking 302mg vitamin C. Fortunately, a lot of days passed when I forgot to get our gummies. Still, we were taking more than 300% of the recommended daily Vitamin C dose (90 for 80 year old man and 75 for an 80 year old woman) on many days.
There are advocates for much higher doses. The Linus Pauling Institute recommends upwards of 400mg.
Certainly, vitamin C is essential to human life. This vitamin must be introduced externally because humans, unlike some other animals, do not have the ability to produce vitamin C. Because of evolutionary developments, the gene that allows us to create our own vitamin C has been deleted. We share the inability to create vitamin C with "other primates, flying mammals, guinea pigs, and some bird and fish species". These animals are also missing the vitamin C-generating gene. Most vertebrates have this gene and don't need to supplement diet with vitamin C. However, if we don't introduce it from an external source, we will die.
This excerpt from an NIH publication summarizes some of the ways our bodies use vitamin C:
Vitamin C is required for the biosynthesis of collagen, L-carnitine, and certain neurotransmitters; vitamin C is also involved in protein metabolism [1,2]. Collagen is an essential component of connective tissue, which plays a vital role in wound healing. Vitamin C is also an important physiological antioxidant [3] and has been shown to regenerate other antioxidants within the body, including alpha-tocopherol (vitamin E) [4]. Because vitamin C can limit the damaging effects of free radicals through its antioxidant activity, researchers are examining whether it might help prevent or delay the development of diseases in which oxidative stress plays a role, such as certain cancers and cardiovascular disease (CVD). In addition to its biosynthetic and antioxidant functions, vitamin C plays an important role in immune function [4] and improves the absorption of nonheme iron [5], the form of iron that is present in plant-based foods. Insufficient vitamin C intake causes scurvy, which is characterized by fatigue or lassitude, widespread connective tissue weakness, and capillary fragility [1,2,4,6-9].
Because humans cannot generate their own vitamin C, they have evolved a very efficient mechanism for absorbing externally consumed vitamin C, and for excreting it. Excretion is accomplished through the kidneys.
This excerpt from the NIH explains how the body regulates vitamin C absorption:
The body tightly controls tissue and plasma concentrations of vitamin C. Higher doses of vitamin C have lower absorption than moderate doses, and absorbed, unmetabolized ascorbic acid is excreted in the urine.
What problem could arise from high doses of vitamin C? The most commonly mentioned issue is kidney stones. A 2015 report published by the U.S NIH showed that increased vitamin C intake (mean dose 700mg a day) resulted in significant increase in kidney stone formation for men but not for women. Subsequent studies confirm this association in men. The stones apparently form because oxalate is produced in urine excretion (from vitamin C). It is the accumulation of oxalate that results in the kidney stone.
There also have been cases of severe kidney injury as result of high vitamin C intake. Generally this damage results from megadoses, either intravenously administered or taken orally as supplements. These megadoses may be as high as 2 gm (!!) a day, but damage has been noted with a dose as low as 480 mg.
The culprit in these cases of kidney damage once again is oxalate. The oxalate damages the tubes in the kidneys and results in a condition called oxalate nephropathy. People at highest risk for developing this condition are those suffering from BPH (benign prostate hyperplasia), gastric bypass, bowel resection, and obstructive bowel disease. Sometimes the damage to the kidneys is so great as to lead to kidney failure, which may require lifelong dialysis.
Why do people take megadoses of vitamin C? An article published by Sloan Kettering discusses some of the more common theories about the benefits of therapeutic vitamin C. The website lists four common uses:
The website assesses some of these claims. It asserts that the effect on the common cold, with zinc supplementation, is minimal. The authors do add that there is a noted benefit in infants born to mothers who smoke. These infants had improved respiratory function. However, with regard to cardiovascular health, there was no perceived benefit and in some cases there was even an increased risk of mortality. As for cancer therapy: the results are 'mixed'. While patients on chemo may experience vitamin C deficiency, it's also true that cancer cells seem to preferentially uptake vitamin C.
I looked up wound healing on a separate site. In a publication called 'Antioxidants', a report was published that looked at 18 studies on wound healing. Overall, treatment with vitamin C was helpful in treating one type of wound: pressure ulcers. The authors of the article suggest studies on other conditions were not large enough to be useful. However, they do recommend that vitamin C supplementation be considered in the treatment of pressure wounds.
Conclusion:
I began my reading about vitamin C and kidney damage because of a concern my daughter raised. I don't think I've done any harm to my husband by pumping him with 300mgs of vitamin C on an inconsistent basis, but I won't do it anymore because I do worry about the accumulation of oxalate. I will continue with the modest dose of C and our modest multivitamin. If any health issues develop that I think might benefit from C augmentation, I will raise those issues with his doctor and perhaps ask that serum levels of C be tested.
I hope some of my readers find information in this blog helpful.
Thank you for reading.
Peace and health to all. Hive on!
https://pmc.ncbi.nlm.nih.gov/articles/PMC10776057/
https://www.medicalnewstoday.com/articles/vitamin-c-and-kidneys#summary
https://www.renalandurologynews.com/features/do-not-ignore-vitamin-c-management-in-ckd/
