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.

Correcting Vitamin D Deficiency May Decrease Risk of Heart Disease

Vitamin D is a steroid hormone and a component of a complex endocrine pathway sometimes called 'vitamin D endocrine system' (Medscape, 2012).  In a recent study, 9,400 patients had an average vitamin D level of 19.3 nanograms per milliliter - levels of 30 are generally considered "normal". At their next follow-up visit, 50% of patients had raised their vitamin D levels to above 30 nanograms per milliliter.

Compared with patients whose vitamin D levels were still low, patients who raised their vitamin D levels were 33% less likely to have a heart attack, 20% less likely to develop heart failure, and 30% less likely to die between the two visits (source: WebMD).

"While normal has generally been considered to be 30, some people have suggested 40 or 50 is better. People who increased their vitamin D blood level to 43 nanograms per milliliter had the lowest rates of heart disease and stroke. But increasing it beyond that, say to 60 or 70, offered no greater benefit."

One of the BMJ blogs calls vitamin D "the elixir of life", but it all starts to sound a bit too good to be absolutely true.

What is the best test to diagnose vitamin D deficiency?

Serum 25(OH)D.

The circulating half-life of 25(OH)D is 2 weeks. This is the best test to determine vitamin D status. A 25(OH)D level of less than 32 ng/mL is considered vitamin D insufficient because intestinal calcium absorption is optimized at levels above 32 ng/mL.

A 25(OH)D level of less than 15 or 20 ng/mL have been used to define vitamin D deficiency.

Parathyroid hormone levels start to rise at 25(OH)D levels below 31 ng/mL, which is another marker of vitamin D insufficiency. Although not always required for the diagnosis of vitamin D insufficiency, a serum PTH may be used to help establish the diagnosis of vitamin D insufficiency.

The word vitamin was originally derived from Funk's term "vital amine."

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:
Vitamin D Supplements Lower Heart Disease Risk. WebMD.

Low vitamin D levels in children associated with higher plasma glucose and lower HDL

Vitamin D deficiency occurs frequently in COPD and correlates with severity

Image source: Wikipedia, public domain.