How Much Vitamin D Should You Take?

How Much Vitamin D Should You Take?


“How Much Vitamin D Should You Take?” Randomized, controlled,
clinical trials have found that vitamin D supplements
extend one’s lifespan. What is the optimal dose? What blood level is associated
with living longest? In my nine-part video series on vitamin D
back in 2011, I noted that the relationship between vitamin D levels and mortality
appeared to be a U-shaped curve, meaning low D levels were associated
with increased mortality, but so were levels that were too high,
with the apparent sweet spot around 75 or 80 nmol/l, based on
individual studies like this one. Why might higher D levels be
associated with higher risk? Well, this was population study, so
you can’t be sure which came first. Maybe the higher vitamin D
led to higher risk, or maybe higher risk
led to the vitamin D, meaning maybe those who weren’t
doing as well were prescribed vitamin D. Maybe it’s because these
were Scandinavian studies, where they tend to take a lot of cod liver
oil as the vitamin D supplement, one spoonful of which could exceed
the tolerable upper daily limit of intake for vitamin A, which could
have negative consequences even if you don’t inject it
into your penis. I was surprised to see cod liver oil
listed among the long list of things men have tried to inject into
themselves because they felt they were coming up short, though may have ended up even shorter
after all the reconstructive surgery. Anyways, the U-shaped
curve is old data. An updated meta-analysis has shown
that as population vitamin D levels go up, mortality appears to go down and
stay down, which is good because then we don’t have to test to see if
we’re hitting just the right level. Routine testing of vitamin D
levels is not recommended. Why? Well, it costs money, and in
most people levels come right up to where you want them with
sufficient sun or supplementation, so they figure what’s the point? But also because the test
is not very good — results can be all over the place. What happens when you
send a single sample to a thousand different labs
around the world? You’d maybe expect a little
variation, but not this. Results from the same sample ranged
anywhere from less than 20 to over 100. So depending on what lab your doctor
sent your blood sample to, the results could have placed you here, or here,
so not necessarily very helpful. So what’s a safe dose that will likely
get us to the purported optimal level? A thousand units a day should get most people
up to the target 75 nmol/l (which is 30 ng/ml), but by ‘most people’ they mean 50%. To get around 85% of the population
up to 75 would require 2,000 a day. 2,000 international units a day would
shift the curve from here to here. That way we can take the average
person into the desired range without fear of toxicity. You can
take too much vitamin D, but you don’t tend to see problems
until blood levels get up around 250 which would take consistent
daily doses in excess of 10,000. Note that if you’re overweight
you may want to take 3,000, or if obese, even more than that. If you’re over age 70 and not
getting enough sun, it may take 3,500 units to get that same 85% chance
of bumping your levels past the target. Again, no need for the average person to test
and retest since a few thousand a day should bring almost everyone
up without risking toxicity. OK, but then why did the
Institute of Medicine set the Recommended Daily
Allowance at 600 to 800 units? In fact, official recommendations
are all over the map, ranging from just 200 a day,
all the way up to 10,000 a day. I’ll try to cut through
the confusion next.