Why Vitamin A May Not Be as Useful or Harmless as
You Thought

http://articles.mercola.com/sites/articles/archive/2009/01/03/why-vitamin-a-may-
not-be-as-useful-or-harmless-as-you-thought.aspx

A landmark paper from the Vitamin D Council
asserts that a form of vitamin A, retinoic acid,
can block the activity of vitamin D by weakly
activating the vitamin D response element on
genes. Since vitamin D levels are crucial for
human health, that means it is essential to have
the proper ratio of vitamin D to vitamin A in your
body.

This means that vitamin A supplementation is
potentially dangerous. Vitamin A production is
tightly controlled in your body, the source
(substrate) being carotenoids from vegetables in
your intestine. Your body uses these carotenoid
substrates to make exactly the right amount of
retinol. But when you take vitamin A as retinol
directly, such as in cod liver oil, you intervene
in this closed system and bypass the controls.

The goal is to provide all the vitamin A and
vitamin D substrate your body would have obtained
in a natural state, so your body can regulate both
systems naturally. This is best done by eating
colorful vegetables and by exposing your skin to
sun every day. *(see note at end)

Sources:
Vitamin D Newsletter December 2008

 Dr. Mercola's Comments:
As scientific findings about vitamin D’s health
benefits race forward at breakneck speed, another
issue has surfaced – the synergistic effects of
vitamin A on vitamin D. More specifically, how
people in developed countries are potentially
sabotaging the multitude of health benefits they
could receive from adequate vitamin D, by taking
excessive amounts of vitamin A, either in the form
of multi-vitamins or cod liver oil.

I have spent many hours carefully analyzing this
issue over the past three months, and as a result,
I’ve already issued a revision of my long held
recommendation for cod liver oil. If you missed
that important update, please take the time to
review it now.

My previous recommendation was based on the fact
that cod liver oil contains vitamins D and A in
addition to healthy omega-3 fats. These vitamins
are essential for most everyone who cannot get
regular sun exposure year-round.

However, more recent research offers compelling
evidence that the ratios of these two vitamins may
be of paramount importance in order to extract
optimal health benefits.

Vitamin A, which is essential for your immune
system just like vitamin D, is also a precursor to
active hormones that regulate the expression of
your genes, and they work in tandem. For example,
there is evidence that without vitamin D, vitamin
A can be ineffective or even toxic. But if you’re
deficient in vitamin A, vitamin D cannot function
properly either. So proper balance of these two
vitamins is essential. Too much or too little of
either may create negative consequences.

Unfortunately, modern cod liver oil does not
supply these vitamins in healthy ratios to each other.

Think of it as the issue of omega-3 vs omega-6.

Their ratio should be close to 1:1, but our modern
diet, high in processed foods, has thrown this
balance so far out of whack that omega-3
supplementation is essential for nearly everyone,
while at the same time reducing your intake of
omega-6 is highly recommended.

The issue of vitamin A and vitamin D is very similar.

Unfortunately, we simply do not yet know the
optimal ratios between these two vitamins, but it
is clear that nearly all cod liver oil products
supply them in levels that do not appear to be
ideal.  Manufacturers are free to add or subtract
as much vitamin A or D as they see fit.

It’s All About Balance

One of the most important pieces of new
information that influenced my thinking on this
issue was two recent meta-analyses. The first one
showed that people who took vitamin A in the form
of cod liver oil or other supplements, had a 16
percent increase in dying .

The other study showed that unlike third world
countries where vitamin A supplementation appears
to decrease infections, vitamin A supplementation
in developed countries like the U.S. actually
increased infections.

How could that be?

This is where the appropriate ratios come in.

The researchers believe these results are due to
massive vitamin A deficiencies in the third world,
because most of their calories are from grains,
and they simply don’t have an opportunity to
consume as many fresh fruits, vegetables, butter,
eggs and other vitamin A-containing foods that
those in the developed world do.

Conversely, current research have not been able to
find any vitamin A deficiency at all in developed
countries like the U.S, but approximately 5
percent have vitamin A toxicity.

Moving on to vitamin D.

There’s mounting evidence that vitamin D protects
against a number of cancers, including colon
cancer. But paradoxically, researchers found that
many of those with higher vitamin D levels do not
seem to have this benefit. Again – it’s likely to
be all about the ratios.

A bright Harvard researcher carefully analyzed the
data and found that when he removed the people
with high vitamin A and high vitamin D levels,
those with normal vitamin A levels and high
vitamin D levels continued to have reduced risk of
colon cancer.

Hence, those who did not supplement with vitamin A
gained the protective effect from higher levels of
vitamin D!

How Excessive Vitamin A Can Interfere with Vitamin
D’s Benefits

Dr. Cannell and other prominent researchers
believe that supplementing with vitamin A can
reduce the effectiveness of vitamin D by
inhibiting the binding of its active form to your
DNA, effectively preventing its ability to
regulate the expression of your vitamin
D-responsive genes.

But before we go further, let’s clarify one thing:
It’s the retinoic acid (retinol) form of vitamin A
that is problematic. Not beta carotene.

Beta carotene is not a concern because it is
PRE-vitamin A. Your body will simply not
over-convert beta carotene to excessive levels of
vitamin A. So taking beta carotene supplements is
not going to interfere with your vitamin D.

Additionally, if you are deficient in vitamin D
and supplement with vitamin A (retinoic acid),
you’re more likely to suffer vitamin A toxicity.

In fact, vitamin A toxicity may be more common
than you think.

Why?

Because vitamin A toxicity can lead to liver
disease, but very few physicians will ever think
to inquire about vitamin A supplements or cod
liver oil when presented with a liver disease case.

One previous study published in the journal
Gastroenterology concluded:

“It was concluded that at least in some western
countries chronic vitamin A consumption might
represent an appreciable cause of chronic liver
disease, the recognition of which mainly relies on
expert liver biopsy interpretation. The data also
indicate that prolonged and continuous consumption
of doses in the low "therapeutic" range can result
in life-threatening liver damage.”

If you search PubMed you’ll find nearly 85 reports
on vitamin A-induced liver disease alone.

So clearly, the key to optimal health is having
the proper ratio of vitamin D to vitamin A in your
body.

How Can You Ensure Proper Ratios of Vitamins A and D?

As Dr. Cannell states, the best way to obtain the
proper vitamin A to D ratio is to obtain it the
way you were designed to obtain it:

Vitamin A through your diet, in the form of
colorful vegetables
*Vitamin D through daily sun exposure on your skin


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*RFNote: The two good doctors seem to have
forgotton that, for many months of the year, in
many countries on the globe there is insufficient
sunlight to provide the required vitamin D. In
this case, take D3 supplements - at least 1,000
IUs twice/day, or one 2,000 IU dose, or even more
per day, if it is available. If, for ANY reason,
you cannot get that sun exposure, just be sure to
take the supplement.