Neglected Nutrients: Vitamin A

The first nutrient we’re going to look at in this series is vitamin A. Vitamin A is part of a class of vitamins that are fat-soluble, meaning they require a fatty-medium for which to dissolve in, and can be stored within the body (specifically the liver in this case) for later use. It is also important to keep in mind that vitamin A cannot be absorbed without sufficient dietary fat present. Accroding to the Linus Pauling Institute, Vitamin A’s many functions include: regulating the growth and differentiation of virtually all cells in the body especially the skin, structure and maintenance of the visual system in the eyes, bone remodeling including the teeth, regulation of gene expression, and immunity. Vitamin A (as well as vitamin D) is critical for the proper development of all the organs of the fetus during pregnancy. It also plays a large role in protecting the mucus membranes of the nose, mouth, throat, and lungs through its promotion of secretory IgA, an antibody used for disabling pathogens and marking them for destruction. 

How’s Your Motivation?

Vitamin A is required to synthesize arachidonic acid, a fatty acid used for the production of compounds the both promote and resolve inflammation. According Chris Masterjohn PhD in his article “The Pursuit of Happiness,”  Arachidonic acid is also used to manufacture compounds within our body called endocannabinoids. He says these molecules (which are also produced by plants, the most-well known being the hemp plant) are potent regulators of homeostasis within the body. He notes that these substances help to control stress hormone output and dopamine production, which is a neurotransmitter responsible for the feeling of pleasure and reward. Dopamine is also necessary for promoting goal-oriented behavior. Without it, we tend to lack focus, become anxious in social situations, snap easily at others, and become less interested in planning for the future.

Friend or Foe?

Gut immune system

 

 

 

 

 

 

 

 

 

Perhaps vitamin A’s most underappreciated role is in the maintenance of intestinal immunity. Michael Ash, B.Sc. (Hons) D.O. N.D. F.Dip ION talks extensively about this subject in his article “Vitamin A: The Key to a Tolerant Immune System.” He writes:

The cells along the vast mucosal surfaces of your body are constantly in contact with foods, microbes and toxins. They make innumerable immunological decisions every day—so many that a single day’s encounters exceed that of the rest of your immune system over a lifetime. As the gut makes its decisions, it then relays information from the innate to the adaptive, systemic immune system. Mucosal tolerance is a necessity for us to survive; without it we would not live a single day.

Sounds pretty incredible doesn’t it?  That’s because it is. A breakdown in this critical system can result in allergies or even autoimmunity. He notes Vitamin A’s job is not only for the maintenance of the mucosa itself, but it’s also vitally important for the differentiation of naive T-cells into T-regulatory cells. These cells help put the brakes on an out of control immune response, helping to decrease inappropriate inflammation. Ash also emphasizes that T-regs help to control excess IL-17, which is an inflammatory cytokine (signal) thought to be a strong promoter of auto-antibodies. He even suggests the possibility that vitamin A could be used to revert an inflammatory subset of T-cells back to tolerance. This could prove to be a huge breakthrough in the realm of autoimmunity.

A Brief History

Vitamin A was once the king of the vitamins. In the early 1930’s it was touted as the number one vitamin for combating colds and flu, especially those of viral origin such as measles. Dr. Weston A. Price, a dentist who traveled the world observing indigenous cultures and what they ate, noted that each of these cultures had at least one vitamin A-rich food present in their traditional diets. After observing the excellent dental health of these primitive peoples and their lack of dental caries (cavities), upon returning home to the United States, Price used his newly-found nutritional knowledge to reverse patient’s cavities in his own practice. Before this time, vitamin A rich foods were mostly used in the prevention and reversal of night blindness.

Are Carotenoids Enough?

It has been proposed that a worldwide epidemic of vitamin A deficiency could be relieved by the genetic modification of rice to synthesize meaningful amounts of beta-carotene in the edible portion, effectively stopping the epidemic in its tracks. This newly dubbed “Golden Rice” is being pushed There is one problem with this though. Beta-carotene is not vitamin A. Although it’s commonly mislabeled as such, beta-carotene must still be converted to retinol, before it can be synthesized into more biologically-active derivatives. And there’s a problem with this. Not everyone converts beta-carotene to retinol at meaningful rate, and sometimes the conversion doesn’t happen at all. We used to think that beta-carotene was converted to retinol at rate of 2 beta-carotene units to one retinol unit. However, since then, according to Dr. Kate Rheaume-Bleue in her book Vitamin K2 and the Calcium Paradox, several studies have looked at this theory and found that the actual conversion is anywhere from 6:1 all the way to 48:1. Meaning it can take as little as 6 units of beta-carotene to as many as 48 units to equal one international unit (IU) of retinol. It may be safe to say that those who have subsisted on a mostly plant-based diet may be more genetically well-adapted to converting carotenoids into retinol, however, this assumption could prove to be costly for those with a zinc deficiency. According to Masterjohn in his article “Nutritional Adjuncts to the Fat-Soluble Vitamins,” zinc plays an important role in not only the absorption of carotenoids, such as beta-carotene, but also to the utilization and conversion to vitamin A. And since zinc is a mineral that is hard to obtain in meaningful amounts from plant sources, this further complicates the picture. To complicate matters even further, we now know thanks to Sally Fallon and Mary Enig PhD in their article “Vitamin A Saga,” that various genetic defects, low fat intake, intestinal roundworms, diarrhea, hypothyroidism, celiac disease, pancreatic disease, and diabetes also affect the conversion of beta-carotene to retinol and in some cases virtually inhibit this conversion.

Given what we know about vitamin A’s undisputed role in maintaining mucosal membrane integrity and immune tolerance, I challenge those out there who in fact believe we are obtaining a sufficient amount of vitamin A in our diets, and point them to the steadily rising incidence of allergies and autoimmune disorders our society is currently plagued with.

Where Can We Get It?

SourcesOfvitaminA

 

 

 

 

 

 

 

 

 

For the reasons I stated above, I advocate acquiring pre-formed vitamin A from animal sources instead of relying on conversion from plant carotenoids. Sources of pre-formed vitamin A include liver, egg yolks, grass-fed butter, salmon, cod liver oil, raw milk and cheeses derived from raw milk.

A Word About Toxicity

The argument against the supplementing or the dietary consumption of pre-formed vitamin A has led to an overall negative perception of this commonly misunderstood nutrient. Chris Masterjohn has written extensively about this subject but I’ll provide a few excerpts in order to ease reader’s concerns pertaining to this. In his article “The Cod Liver Oil Debate,” Masterjohn gives some insight on the cooperative actions of both vitamin A and D:

Developments in molecular biology over the last several decades have shown that vitamins A and D carry out most of their actions by binding to specific receptors that will bring them into contact with DNA inside the nucleus of a cell, in order to alter the expression of genes by turning them on or off or by turning them up or down. The receptors for these vitamins, together with those for thyroid hormones, steroid hormones, and other important signaling molecules, are part of a common family of nuclear receptors that interact with one another. Vitamin A is especially involved in these interactions—it not only carries out its own signaling, but forms an essential partnership with most other nuclear hormones, which allows them to carry out their functions. Recent research, described in more detail in the sidebar on page 22, has shown that vitamin D can only effectively control the expression of genes in the presence of vitamin A.

A fine example of this is the thyroid nuclear receptor which binds to the active thyroid hormone T3 and allows the hormone to exert its action on the cell. Once thyroid hormone physically binds to the receptor, derivatives of vitamin A and D must be present to allow the alteration of genetic expression by the hormone, which commonly results in increased metabolic rate. So having sufficiency in one vitamin but not the other, creates and increased need for its partner. The point being: Vitamin A is only toxic in the presence of a vitamin D deficiency. With this information in mind and based on the available research, intakes of 5000-10,000IUs of pre-formed vitamin A per day from all sources (supplements and food) appear to be both safe and beneficial.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s