Is Vit C safe info

[Guest guest]

I just found this website. The last line sums it up.

http://lpi.oregonstate.edu/f-w99/kidneystones.html

What About Vitamin C and Kidney Stones?

Lawson

LPI Adminstrative Officer

For many years, experts have speculated that the intake of large amounts of

vitamin C may contribute to the formation of oxalate-type kidney stones because

of the metabolic conversion of vitamin C to oxalic acid. If the amount of

oxalic acid in the urine increases as the dose of vitamin C increases, they

reasoned, then a prolonged intake of large amounts of vitamin C may cause kidney

stones. Some experimental evidence supports this concern. For instance, Dr.

Constance Tsao, formerly with the Linus ing Institute of Science and

Medicine,

published two studies in the 1980s that investigated the relationship between

vitamin C and oxalic acid. In one study, Dr. Tsao demonstrated that doses of

3-10 grams/day of vitamin C taken by ten subjects for 2-10 years did not

result in abnormal levels of oxalic acid in the blood. In the other study,

however,

she showed that the ingestion of 10 grams/day of vitamin C by six subjects

resulted in slightly elevated levels of oxalic acid in the urine, although the

amount was within the range obtained by the consumption of normal diets. In

contrast, a study with six subjects published in 1996 by Dr. Mark Levine and

colleagues at the National Institutes of Health found that increasing the daily

intake of vitamin C from 200 mg to 1,000 mg resulted in an increase in urinary

oxalic acid of about 30%. Consequently, Dr. Levine suggested that the " upper

safe doses of vitamin C are less than 1,000 mg daily in healthy people " ,

although he noted that several earlier studies had not found any association

between

the incidence of kidney stones and the regular daily intake of 1,000 mg or

more of vitamin C.

Dr. Carol ston of Arizona State University published an article in

Nutrition Reviews in March in which she reviewed the scientific and medical

evidence

that might allow the establishment of an " upper intake level " for vitamin C.

She examined the evidence on " rebound scurvy " , kidney stones, hemolytic anemia

in patients with glucose-6-phosphate dehydrogenase deficiency, enhanced iron

absorption, pro-oxidant effects, and the destruction of vitamin B12. She noted

that the experimental, clinical, and epidemiological evidence does not

support a detrimental role for vitamin C in any of these conditions, although we

still do not know the effect of large amounts of vitamin C in people with

hemochromatosis, or iron-overload disease. Her analysis is in agreement with the

many

other reviews of the safety of supplemental vitamin C. Dr. ston concludes

that " the available data indicate that very high intakes of vitamin C (2-4

g/day) are well tolerated biologically in healthy mammalian systems. Currently,

strong scientific evidence to define and defend a UL [Tolerable Upper Intake

Level] for vitamin C is not available. " In other words, we cannot establish a

threshold of toxicity for vitamin C.

To this evidence, we can add another recently published study by Dr.

Curhan and colleagues at Harvard, Brigham and Women’s Hospital, and

Massachusetts

General Hospital. For 14 years, Dr. Curhan et al. followed a group of 85,557

women with no prior history of kidney stones. Their intake of vitamin B6 and

vitamin C was assessed and correlated with the development of stones. Daily

intakes of 40 mg or more of vitamin B6 provided significant protection against

the formation of stones, but there was no significant difference in stone

formation between the groups with the lowest (less than 250 mg/day) and highest

(1,500 mg/day or more) intake of vitamin C. In a previous study of a group of

over

45,000 men followed for 6 years, the authors found a protective role for

vitamin C but not for vitamin B6. They conclude, " ...our findings for vitamin C,

which have been consistent for women and men, do not support the practice of

routine restriction of vitamin C to prevent kidney stones. " Addressing previous

experimental studies that associated vitamin C with increased urinary oxalate

(the salt of oxalic acid), the authors point to another study from 1994, which

showed that vitamin C is easily converted to oxalate during analytical

procedures. Therefore, the increased amounts of oxalate observed in urine may

have

been artifactually produced and have no relation to what happens in the body.

The accumulated evidence demonstrates that vitamin C, even in large amounts,

is a remarkably safe substance. This evidence strongly supports the role of

vitamin C as an important antioxidant, not a pro-oxidant. While we know that the

relatively small amount of 100-200 mg/day provides substantial protection

against age-related diseases, including heart disease, cancer, and cataract, and

that a still smaller amount prevents scurvy, we do not yet know the optimal

amount of vitamin C (see " The Optimal Intake of Vitamin C " by Lawson,

LPI Newsletter Spring/Summer 1997). Large doses of vitamin C have been shown to

be of therapeutic benefit in promoting relaxation of the arteries

(vasodilation), which benefits patients with heart disease and " coronary risk

factors " ,

such as diabetes, high serum cholesterol levels, and high serum homocysteine

levels. Large doses of vitamin C are also useful in combating viral infections,

preventing toxemia in pregnant women (possibly through vasodilation), and as an

adjunct to the appropriate conventional treatment of cancer. There is also a

tremendous amount of anecdotal evidence and some clinical evidence that

vitamin C may be of benefit in treating other illnesses and conditions. The

difficulty of determining the optimal intake of vitamin C is due to its many

different

functions in the body, biochemical individuality, and the impracticability of

measuring the vitamin C content of various tissues and organs in healthy

people in order to correlate those amounts with blood levels and optimal

function.

Over twenty years ago, Linus ing proposed that the RDA for vitamin C

should be increased to 200 mg/day. At about the same time, he mustered

theoretical

and experimental arguments to support his belief at that time that the

optimal intake for humans is about 2 grams/day. While the merits of ingesting

that

much vitamin C or more each day are debatable, at least we can be confident

that large doses are not harmful for healthy people and may be of therapeutic

benefit in many cases. In particular, the concern about the role of vitamin C in

kidney stone formation, a source of speculation for several decades, appears

to be no longer justified.

Last Update: Monday, 29-Sep-2003 15:32:20 PDT