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Ask the Wellness Educator Balancing Vitamins D and A

I have read comments that Vitamin A (retinol) interferes with Vitamin D absorption, so you should minimize the amount of preformed A taken to a relatively small amount (1-2000 IUs).

If I were to take Vitamin D and multi with Vitamin A several hours apart, would that obviate the issue? Are there other possible Vitamin D antagonists? Do you find different responses to different kinds of delivery systems (liquid, softgel, capsules)?

My concern is based on the fact that my Vitamin D levels are still low despite taking 4000 IU/day, mostly in liquid form, but taken close to the same time as the multivitamin.


Cornelius, Philadelphia, PA

Dear Cornelius,

These are great questions, but challenging to give answers because they are the subject of considerable controversy. Despite the large amounts of attention that vitamin D has garnered over the past few years, there are still a lot of unanswered questions and resulting controversial opinions.

Vitamin A & D may compete for absorption; although each has its own receptor in cells, they also share one particular receptor called RXR. Some experts believe that because of this overlapping receptor, taking an excess of one vitamin will impede the uptake of the other one. On the other hand, some experts believe that the body will absorb only what it needs of both vitamin D3 and pro-vitamin A (carotenoids) and creates balance on its own.

One foundational problem is the lack of agreement on the safe and appropriate dose of vitamins D and A and on what is considered toxic. The recommended dosage for D3 ranges between 400 IU and 5000 IU daily, while vitamin A recommendations can be between 5000 and 20,000 IU, depending on the biochemical requirements of the individual. What is clear is that there are surprisingly high deficiency rates in the US for both vitamin A and vitamin D, so the majority of people probably need to supplement both. Balance is key, but the necessary ratio for each individual's requirements is difficult to define.

A and D are fat-soluble vitamins, so they can accumulate in tissues, which explains the concern for toxicity. Toxicity is not an issue for carotenes, because they are water-soluble and are converted to vitamin A only as needed. Because fat-soluble vitamins are not excreted quickly, separating their dosage by a few hours is probably not going to make a significant difference. You do want to balance the overall levels in the body, including fat-soluble vitamin E and fat-soluble vitamin K.

Beyond vitamin A, there are some other factors that can interfere with vitamin D absorption or synthesis. Some medications might interfere with absorption, such as acid blockers, anti-seizure medications, corticosteroids, and mineral oil. There is also a common genetic alteration that may impair a person's ability to convert vitamin D to its active form, making it difficult to raise serum levels.

There are a few things you can do to enhance your vitamin D uptake without increasing the dosage. Because it is a fat-soluble vitamin, it will absorb best when taken in an oil matrix, like a softgel or oil-based liquid, or taken with a meal that contains some fat. Also, balance supplementation with inspiration from the sun. You must be exposed to UVB light, which is generally only available between 11 AM and 2PM in most of the US. The amount of time you need to be exposed to trigger D3 synthesis varies widely between individuals, however, just be sure to not stay out too long, indicated by the skin turning pink.

-Jennifer Palmer, N.D.

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