Vitamine A supplementen beïnvloeden voordelen vitamine D duidelijk negatief*
Wat onderzoekers in 1993 al vaststelden, dat retinol (vitamine
A) de werking van vitamine D flink negatief beïnvloedt, is door een grote Europese studie bevestigd. Uit deze
studie over de grote voordelen van vitamine D tegen darmkanker blijkt bij nadere bestudering door wetenschapper Dr. Grant dat door
aanvulling met vitamine A de grote voordelen van vitamine D teniet gedaan worden. Extra inname van
bètacaroteen is geen probleem omdat daarvan het lichaam naar behoefte vitamine A kan aanmaken en in het lichaam geen overmatige hoeveelheid retinol is.
Vitamin A Supplements may Negate Benefits of Vitamin D
Most of you are well aware that vitamin D has a legion of health benefits crucial to every one of us. What is alarming is the latest research in the British Medical Journal, which appears to confirm: that a form of vitamin A in surprisingly small doses may negate many of the beneficial health effects of vitamin D. This is the largest study to date showing vitamin A blocks vitamin D`s effect.
Dr. William Grant, Ph.D., an internationally recognized research scientist and vitamin D expert, found that about 30 percent of cancer deaths could be prevented each year with higher levels of vitamin D. Given that cancer, heart disease and diabetes are three of the top causes of death in the United States, getting enough of this vitamin should be a top priority. Unfortunately most of us are vitamin D deficient. It is clearly important to avoid anything that might hamper your vitamin D production. Surprisingly, it appears vitamin A supplementation may indeed have this effect.
In a recent article, Dr. John Jacob Cannell, MD, executive director of The Vitamin D Council, discussed the British Medical Journal report. He says:
"The crux of the problem is that a form of vitamin A, retinoic acid weakly activates the vitamin D response element on the gene and perhaps blocks vitamin D`s more robust activation." In fact, the authors of a 1993 study state, "there is a profound inhibition of vitamin D-activated...gene expression by retinoic acid."
The distinction is between various forms of vitamin A.
It is 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 foods with beta carotene or taking beta carotene supplements are not going to interfere with vitamin D.
In addition, Dr. Cannell goes on to say, "As I began reviewing the latest research, I realized there was compelling evidence that the ratios of these two vitamins may be of paramount importance in order to extract optimal health benefits. It`s important to understand the two work in tandem. But if you`re deficient in vitamin A, vitamin D cannot function properly either."
Proper balance of these two vitamins is essential; however, the optimal ratios are unknowable at this
point.
Most of us can remember our grandparents using cod liver oil as the Holy Grail for health. But it seems nearly all cod liver oil products supply vitamins A and D in levels that are not ideal.
This means that a "vitamin A supplementation is potentially dangerous. Vitamin A production is tightly controlled in your body, the source being carotenoids from vegetables in your intestine. Your body uses these carotenoids 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 summary advice is to avoid cod liver oil, avoid multivitamins that have the retinol form of vitamin A, and eat a variety of colorful vegetables along with limited daily sun exposure.
You might also want to obtain a 25-hydroxyvitamin D test to make sure your vitamin D blood levels are between 50-80 ng/mL.
Vitamin D has necessary co-factors that the body needs in order to utilize vitamin D properly. They are: magnesium (the most important), zinc, vitamin K2, boron, genistein, and a tiny amount of Vitamin A.
(Juni 2010)
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