If you are taking 500 mg or more vitamin C daily, there is something you need to know. Vitamin C (in excess) can become a toxin that can lead to kidney stones, arthritis, other pain conditions, and perhaps, compromised brain function.  For decades we have been told that vitamin C is good for us and may help prevent colds. But too much of a good thing can make trouble. (Research has not been able to confirm the theory that vitamin C supplements help to prevent colds unless you routinely engage in physically demanding work or endurance sports.)

The body tends to metabolize excess vitamin C into a corrosive acid called oxalic acid. This acid immediately steals minerals like calcium as it becomes oxalate. As the kidneys remove oxalate from the blood, calcium oxalate can grow into crystals in the kidneys or elsewhere in the urinary tract causing painful stones. Over time, if the kidneys are forced to handle excessive amounts of oxalate everyday, kidney failure is likely. This is how taking 500 mg or more of vitamin C can promote a loss of kidney function. Perhaps the modern habit of taking extra vitamin C is contributing to the rising rates of kidney stones. One estimate suggests that half of us will get a kidney stone in our lifetime.

Oxalates in the body that are not removed by, or stuck in, the (perhaps struggling) kidneys can get lodged in other tissues of the body and cause trouble there too.  Oxalate crystals have been found in every human tissue including bones, joints, glands – especially the thyroid, blood vessels, arterial plaque, eyes, lungs, and skin.  These crystals are sharp and irritating, and they may trigger an immune response and promote inflammation. They may also generate free-radicals that can damage cell membranes and damage the cell organelles, especially the mitochondria which are important energy producers.

When a cell attempts to dissolve the oxalate crystal deposits, oxalate molecules or ions may move around and trigger episodic pain or difficulty with brain and nerve functions. Sleep, concentration, memory, and thinking can all be affected by the movement of oxalates in and around neurological tissues.  Likewise, bone problems and joint pain can result from calcium oxalate deposits which may become more likely when excess amounts of vitamin C are taken.

How much vitamin C is safe?

The RDA for C (ascorbic acid) is 75 mg for adult females and 90 mg for adult males. This sounds like very little, but even as little as 10 mg is enough to avoid scurvy – the vitamin C deficiency disease.  A daily intake of 150-200 mg of C is considered safe for most people and is under the threshold that seems to generate additional oxalate in the body. Most people can get that much from typical diets that contain some vegetables or fruits. To illustrate the point, see the tables below. I offer two hypothetical diets: 1) a diet with many healthy fresh foods, and 2) a diet of mostly fast food. (Just major ingredients are listed in the tables.)

The diet of healthy, fresh foods listed in Table 1 is not necessarily my recommended diet, but it comes close. Notice that a lunch of beef stew with a salad composed of romaine lettuce and ¼ of a red bell pepper provides over 60 -70% of the RDA by itself. If the dressing was made with lemon juice, that would add 5 mg more and bring the vitamin C content of the lunch up to 59 – 66 mg. Add 2 sliced radishes (~4 mg vit C.) to bring the vitamin C content of lunch to nearly 70 mg (78 – 93% of the RDA). Of course, many people skip the salad option at lunch and instead select convenience foods, as in my hypothetical fast food diet in Table 2 below.

Lets a look at the diet of fast foods with no extra fruits or vegetables (Table 2) which only gets us about 25% of the RDA. The addition of just ¼ of a fresh bell pepper (38 mg C) and 1/2 cup of raw cantaloupe (23 mg C) would bring the fast-food diet up to the RDA for vitamin C.  Of course, adding bell pepper and cantaloupe cannot correct the many other deficiencies and problems created by a fast-food diet.

These tables are intended to illustrate the point that vitamin C requirements can be met when fresh vegetables or citrus fruits are included in the diet. There is no need for a daily vitamin C supplement if you eat fresh vegetables daily – broccoli with dinner or a simple salad can get you there. Remember, however, that the body does not store vitamin C, so you need to eat foods with vitamin C every day.  Make my favorite dressing tonight, and  enjoy a delicious salad tomorrow.

There is no need for a daily vitamin C supplement if you eat fresh foods – everyday. If you do take vitamin C containing supplements or C fortified foods keep it at a safe level – which seems to be between 150 – 250 mg.

More about Vitamin C, Oxalates and Health:

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