How Much Vitamin D
Should YOU Be Taking?
Vitamin D may now be the most hyped vitamin supplement on the internet, which means we should assess it very carefully before jumping on the vitamin D bandwagon. That may sound like a pretty safe statement to you, but some of the vitamin’s most ardent supporters – and they’re not hard to find with a simple online search – would find it quite controversial.
You know something’s askew when prudent moderation is considered controversial. This post intends to dissect the current state of the evidence about vitamin D – most of it still from weak studies showing associations between low levels of vitamin D and many diseases, but few that show these conditions are actually caused by low vitamin D levels.
That will change as the results of a large randomly-controlled clinical trial are revealed. Unfortunately, that won’t be for several years (read more about this much-awaited trial here).
Until then, the debate will be plagued by poorly-designed and under-powered studies producing conflicting results (for an example of the debate these produce, see this article on the New York Times Well Blog).
The recommendations from alternative health gurus tend to be aggressive – suggesting doses of 5,000 IU (international units) a day and more – while conventional medicine takes a more cautious approach.
This video of Diane Sawyer interviewing Dr. Oz about vitamin D has some misinformation, but is generally on track. His recommended doses are on the high side (see next video for more modest recommendations from actual vitamin D experts) and his suggestion of cod liver oil is a bad one. Cod liver oil is very high in vitamin D, but it’s also very high in vitamin A that competes for absorption with vitamin D and may be harmful at the levels contained in cod liver oil.
The following video, recently produced by Science Magazine, interviews two preeminent vitamin D researchers. Note their measured recommendations for dosages of 2-3,000 IU daily vs. the 5,000 and higher commonly recommended by vitamin D proponents:
Few in either camp would argue that low vitamin D isn’t a problem – both traditional vitamin D deficiency most notably associated with the bone condition of rickets and higher levels that still represent a vitamin D deficit if not an outright deficiency.
Deficiency or Deficit?
These are measured by blood tests and can generally be described as follows:
Vitamin D deficiency = under 10 ng/mL (nanograms per militer of blood volume); and
Vitamin D deficit = 10-20 ng/mL (this is also called an insufficiency).
Before delving deeper into the nuances of whether to supplement with vitamin D and, if so, how much to take, let’s step back briefly for a bigger picture perspective.
Vitamin D is best produced with prudent exposure to the sun’s UVB rays.
Light-skinned people generally get sufficient vitamin D from 10-15 minutes exposure to arms and legs 2-3 days a week during summer months, but sunscreen can block out UVB rays and decrease vitamin D production.
There are two main factors for vitamin D production:
Your sun exposure – The angle of the sun’s rays in northern climes, including most of the U.S., is less conducive to vitamin D production than southern climes. It’s also different at different times of the day. The 10-15 minutes cited above assumes exposure between roughly 10 AM and 3 in the afternoon or, ideally, between 11 AM and 1 PM; and
Your skin’s ability to convert UVB rays – Skin pigmentation is the main factor, although older adults are also less able to produce vitamin D with limited sun exposure. It’s no accident of history that dark-skinned people populate southern climes – their skin can better resist the harmful effects of excessive sun exposure, while lighter-skinned people populate more northern climes with lesser exposure to the sun’s damaging effects.