How much vitamin D do you need? Distilling strong advice from weak evidence

Vitamin D is a steroid hormone and a component of a complex endocrine pathway sometimes called 'vitamin D endocrine system' (Medscape, 2012).

From Nature News:

Vitamin D has been lauded in the media for preventing or treating multiple disease but most evidence is circumstantial or weak.

Despite this, some physicians recommend supplementation of up to 6,000 international units (IU) to compensate for the time that people spend indoors. This is less than what a fair-skinned person make in 30 minutes of exposure to the summer sun (without sunscreen).

The amount spent on vitamin-D supplements in the United States had risen 10-fold in 10 years.

Poor data is one reason that the IOM panel did not recommend higher doses for vitamin D supplementation in 2010. The IOM 1,000-page report recommended that people should aim for blood levels of 50 nanomoles per litre (nmol/L).

However, according to the Endocrine Society's guidelines:

- people with levels under 50 nmol/L are "vitamin-D deficient"
- those with levels between 50 nmol/L and 72.5 nmol/L are "insufficient"

The society's guidelines also offer an 'ideal' level of 100–150 nmol/L which would require 1,500–2,000 IU daily. It advises physicians to monitor vitamin-D levels in healthy people.

Quest Lab already began to implement these deficiency and insufficiency standards over the IOM's. Many physicians are expected to follow suit.

A vitamin D3 dosage of 800 IU/d increased serum 25-(OH)D levels to greater than 50 nmol/L in 97.5% of women http://bit.ly/GzBCcA

References:

The vitamin D-lemma. 6 July 2011 | Nature 475, 23-25 (2011) | doi:10.1038/475023a

Image source: Wikipedia, public domain.

Comments from Google+:

Neil Mehta - This sounds like deja vu' all over again. How many times have we been down this path? vitamin C, Vitamin E, Carotenes....

Common themes:

The myth of natural products: "it is a natural product so it can't cause harm can it?" Thus if a little bit of it is good, more must be better.
The research problem: "It is over the counter and present in foods so very difficult to determine how much someone is actually taking"
Huge confounder of observational studies: "People who take supplements, other "health products" are different from those who don't.