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

vitamin A, vitamin D, vitamins, cod liver oil, cod, omega-3, sunshine, sunA 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.

Vitamin D Dose Recommendations
Age Dosage
Below 5 35 units per pound per day
Age 5 - 10 2500 units
Age 18 - 30 5000 units
Pregnant Women 5000 units
There is no way to know if the above recommendations are correct. The ONLY way to know is to test your blood. You might need 4-5 times the amount recommended above. Ideally your blood level of 25 OH D should be 60ng/ml.
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.


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

For more information about the vital importance of these two vitamins, please review the articles below.

+ Sources and References