How Much Vitamin C Should I Take ? |Dr.Michael Greger

February 29, 2020 0 By Ewald Bahringer


“What is the Optimal Vitamin C intake?”dr michael greger For many years, the RDA, the
recommended daily allowance for vitamins, was just based
on preventing deficiency, with a margin of safety, but the miniscule amount of vitamin C,
for example, needed to avoid scurvy is not necessarily the ideal
intake for optimal health. So what might be the
optimal intake of vitamin C? Let’s ask the body.
How might we do that? By seeing how much the
body absorbs and excretes. If you swallow 15 mg of vitamin C,
which is what you would get eating about a quarter of an orange,
your body sucks up nearly 90% of it. But if you take a supplement
containing 1,250 mg, your body seems to realize that’s too much,
and so clamps down on absorption at the intestinal lining level, and you
end up absorbing less than half. So by doing experiments where
you slowly ratchet up the intake you can see when the body
starts to say, OK, that’s enough, and that magic level of intake
appears to be about 200 mg a day. When you take up to 200 a day
your body sucks it all up, but above that your body tries
to block further absorption suggesting our intestinal vitamin C
transport mechanisms have evolved to fully absorb up to about
200 mg of vitamin C a day. In addition, vitamin C is reabsorbed in
our kidneys back into our bloodstream to maintain our vitamin C blood levels up
at around 70 or 80 micromoles per liter. That’s the shaded region there, which is what you reach at a vitamin C
intake of about 200 mg a day. So even if you take 10 times as
much vitamin C supplements, you know, 2000 mg a day, your
body will just pee and poop it out to keep your blood levels
in that narrow range. So based on these kind of data, one might propose that 200 mg is
the optimal daily intake of vitamin C. You can confirm using disease data. At what daily intake of vitamin C is
there the lowest stroke risk, for example? Apparently at about 200 mg a day. While dietary vitamin C intake was
associated with lower stroke risk, vitamin C supplements
were not, which is consistent with
the overall body of evidence showing that antioxidant
supplements in general don’t seem to protect against
heart attacks or strokes. But wait… Can you get all up to an intake of 200 mg
a day without taking supplements? No problem. Single servings of fruits and
vegetables may have about 50 mg each, so a measly 5 servings
of fruits and veggies a day could get you to
ideal blood levels.