Vitamin D needs some vitamin A, but not too much

Vitamin d recommendations - beyond deficiency - 2011

Ann Nutr Metab. 2011;59(1):10-6. Epub 2011 Nov 25.
Biesalski HK; Department of Biological Chemistry and Nutrition, Food Security Center, University of Hohenheim, Stuttgart, Germany.

Vitamin D plays an important role in regular bone growth and in adequate function of the innate immune system, including barrier functions of mucous membranes. A sufficient supply during pregnancy and lactation protects the child from infectious diseases. Clinical symptoms of severe vitamin D deficiency (rickets) are well known and can be easily detected. Signs and symptoms beyond deficiency, however, remain to be elucidated. Based on clinical and observational data, the plasma level of 25(OH)D may serve as a 'marker' to detect or define a subclinical deficiency. Levels below 50 nmol/l might be insufficient to maintain the non-bone-related activities of vitamin D.

Finally, it has to be considered that all of the nonbone activities of vitamin D are in concert with vitamin A (9-cis retinoic acid). Studies combining both vitamins in sufficient amounts (cod liver oil) demonstrated a beneficial effect on the prevention of respiratory tract infections.

Consequently, it should be strongly recommended to increase the intake of vitamin D and to ensure a daily intake of vitamin A as counseled.

Cod liver oil, vitamin A toxicity, frequent respiratory infections, and the vitamin D deficiency epidemic.

Cannell JJ, Vieth R, Willett W, Zasloff M, Hathcock JN, White JH, Tanumihardjo SA, Larson-Meyer DE, Bischoff-Ferrari HA, Lamberg-Allardt CJ, Lappe JM, Norman AW, Zittermann A, Whiting SJ, Grant WB, Hollis BW, Giovannucci E.
Department of Psychiatry, Atascadero State Hospital, Atascadero, California, USA. jcannell@ash.dmh.ca.gov
Ann Otol Rhinol Laryngol. 2008 Nov;117(11):864-70.
_PDF on VitaminDWiki

From Vitamin D Council Aug 2012

Four years ago, I got 16 nutrition experts together, including Professor Walter Willett at Harvard, to warn about vitamin A once again:

We said
“Although activated vitamin D and vitamin A signal through common cofactors, they compete for each other’s function. Retinoic acid antagonizes the action of vitamin D and its active metabolite. In humans, even the vitamin A in a single serving of liver impairs vitamin D’s rapid intestinal calcium response. In a dietary intake study, Oh et al found that a high retinol intake completely thwarted vitamin D’s otherwise protective effect on distal colorectal adenoma, and they found a clear relationship between vitamin D and vitamin A intakes, as the women in the highest quintile of vitamin D intake ingested around 10,000 IU/d of retinol.”

We also stated
“Furthermore, the consumption of preformed retinol — even in amounts consumed by many Americans in both multivitamins and cod liver oil — may cause bone toxicity in individuals with inadequate vitamin D status. Women in the highest quintile of total vitamin A intake have a 1.5-times elevated risk of hip fracture. Indeed, a recent Cochrane Review found that vitamin A supplements increased the total mortality rate by 16%, perhaps through antagonism of vitamin D. Another recent Cochrane Review concluded that although vitamin A significantly reduced the incidence of acute lower respiratory tract infections in children with low intake of retinol, as occurs in the Third World, it appears to increase the risk and/or worsen the clinical course in children in developed countries.”

Clipped from South Africa Vitamin D web site

Vitamin D requires a small amount of vitamin A (retinol) in order to work correctly.
But vitamin A and vitamin D attach themselves to the same cell receptors.
If you have too much vitamin A, it grabs those cell receptors and leaves no room for vitamin D.

So even though you might have enough vitamin D, it can't work properly if you also have too much vitamin A (retinol).

The precise amount of retinol that inhibits vitamin D is not yet known.
I prefer to supplement less than 2000 IU of retinol daily, and make up for it with extra beta-carotene.

Beta-carotene is a vitamin A precursor found in some green, yellow and orange vegetables.
You can take as much beta-carotene as you please if you obtain it from vegetables.

If you don't eat enough vegetables, take a beta-carotene supplement, about 5000 IU (3 mg) daily.
(You could find this in a good multivitamin).

Your body will get all the vitamin A it needs by converting beta-carotene to retinol.
This process is regulated, so your body will never create more retinol than it requires, and not enough to get in the way of vitamin D.

See also VitaminDWiki

See also web

Substance and its chemical environment Micrograms of retinol equivalent
per microgram of the substance
retinol 1
beta-carotene, dissolved in oil 1/2
beta-carotene, common dietary 1/12
alpha-carotene, common dietary 1/24
gamma-carotene, common dietary 1/24
beta-cryptoxanthin, common dietary 1/24
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