"Do Vitamin C Supplements Prevent Colds but Cause Kidney Stones?"
Mainstream medicine has long had
a healthy skepticism of dietary supplements
extending to the present day. Enough is enough.
But this commentary in the Archives of Internal Medicine
argued that we may have gone too far
as evidenced by our uncritical acceptance of supposed toxicities,
the surprisingly angry scornful tone found in medical texts,
with words like careless, useless, indefensible, wasteful, and insidious,
as well as ignoring evidence of possible benefit.
To illustrate the uncritical acceptance of bad news
about supplements they discuss the well-known concept
that high dose vitamin C can cause kidney stones.
But just because something is well known in medicine
doesn’t mean it’s necessarily true.
They couldn’t find a single reported case.
We’ve known that vitamin C is turned into oxalates in the body,
and if the level of oxalates in the urine
gets too high stones can form,
but even at 4,000 mg of vitamin C a day,
that's like a couple of gallons of orange juice worth,
urinary oxalates may not get very high,
but there may be rare individuals that have an increased capacity
for this conversion into oxalates, and so a theoretical risk
of kidney stones with high dose vitamin C supplements
was raised in a letter printed in a medical journal back in 1973.
OK, but when it's talked about in the medical literature
they make it sound it had been established.
Here’s a reference to 7 citations
supposedly suggesting an association
between excessive vitamin C intake
and the formation of oxalate kidney stones.
Let’s look at the cited sources.
There’s the letter about the theoretical risk—that’s legit,
but this other citation has nothing to do
with either vitamin C or kidney stones,
and the other five citations are just references to books,
which can sometimes be okay
if the books cite primary research themselves,
but instead there’s like this circular logic,
where the books just cite other books
that like cite that theoretical risk letter again.
So it looks like there’s a lot of evidence,
but they’re all just expressing this opinion
with no new data.
By that time there were actually studies
that followed populations of people taking vitamin C supplements
and found no increased kidney stone risk
among men, then later women… same thing.
So you can understand this author's frustration
that vitamin C supplements appeared to be unfairly villainized.
The irony is that now we know that vitamin C supplements
do indeed appear to increase kidney stone risk.
This population of men was followed further out
and men taking vitamin C supplements
did indeed end up with higher risk,
confirmed now in a second study,
though also of men.
We don’t know if women are similarly at risk,
though there has now also been a case reported
of a child also running into problems.
What does doubling of risk mean exactly in this context?
That means those taking like a thousand milligrams a day of vitamin C
may have a 1 in 300 chance of getting a kidney stone every year
instead of a 1 in 600 chance,
which is not an insignificant risk, 1 in 300.
Kidney stones can be really painful,
so they conclude that since there’s no benefits and some risk,
better to stay away.
But there are benefits.
Taking vitamin C just when you get a cold
doesn’t seem to help,
and regular supplement users don’t seem to get fewer colds,
but when they do get sick, they don’t get as sick
and get better about 10% faster,
and those under extreme physical stress
may cut their cold risk in half.
So it’s really up to each individual
to balance the potential common cold benefit
with the potential kidney stone risk.