There seems to be some conflicting data regarding supplementation of FCLO vs Vitamin D and although people always tend to look at Vitamin A (Retinol) negatively, as i did, because of toxicity issues, i really liked this article posted yesterday on the WAPF blog:
Some people say things like "but liver has a lot of retinol and humans have eaten that since the dawn of time". Yeah but, most likely the liver would have been portioned out between people. It wouldn't have been bad for you then, if you only got a piece of the liver which is more realistic than one person taking it. If we believe that offal was highly prized, often above muscle meat, then we also have to realize that one person would not have eaten a whole liver, it would not have been seen as fair.
Depends on what your vit A intake is already. Mine is already super high so I have no urge to supplement. I suspect many other paleo eaters are in a similar situation as the paleo diet tends to provide many good sources of vitamin A. My goal is to keep things in balance and so I only supplement for things I may lack in. For me, in the winter, that is vit D but not vit A. During the rest of the year, it's neither.
I think (as in this is what the evidence tells us so far, as always subject to change) that D supplementation to reach normal blood levels (30-50ng/ml) is fine. What Chris Masterjohn is nervous about is that people might try and go to levels above this, due to the advice of the vitamin D council. This is referenced to a paper by Vieth that I read. Nowhere in that paper does it validate the assertion that 50-80ng/ml is the optimal range, Vieth actually validates the 30-50 range in his conclusions.
On the subject of CLO, a teaspoon a day on days where you don't eat fish or liver is fine. This is tried and tested over generations. The only time we see a negative outcome from a CLO trial is when the CLO is not cold fermented and the A is replaced with synthetic retinol.
The Vit D Council does not advocate CLO because of the antagonistic effect of A on D.
This quote from the paper that the Vit D Council issued:
"Although activated vitamin D and vitamin A signal through common cofactors, they compete for each others 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 also ingested around 10,000 IU/d of retinol." Rohde CM, Deluca HF. All-trans retinoic acid antagonizes the action of calciferol and its active metabolite, 1,25-dihydroxycholecalciferol, in rats. J Nutr. 2005;135(7):1647–1652. Johansson S, Melhus H. Vitamin A antagonizes calcium response to vitamin D in man. J Bone Miner Res. 2001;16(10):1899–1905. Oh K, Willett WC, Wu K, Fuchs CS, Giovannucci EL. Calcium and vitamin D intakes in relation to risk of distal colorectal adenoma in women. Am J Epidemiol. 2007;165(10):1178–1186.
"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." Feskanich D, Singh V, Willett WC, Colditz GA. Vitamin A intake and hip fractures among postmenopausal women. JAMA 2002;287:47–54.
"Indeed, a recent Cochrane Review found that vitamin A supplements increased total mortality rate by 16%, perhaps through antagonism of vitamin D." Bjelakovic G, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev 2008 Apr 16;(2):CD007176.
There is a huge variability in the Vitamin A concentrations of different cod liver oils. I take Carson's and it only has 850 IU per teaspoon. That is only 17% of the RDA.
Considering how many paleo dieters avoid dairy and/or eggs, and that many people have difficulty converting retinol to Vitamin A, Cod Liver Oil is a valid choice for some people. I would be aware of the Vitamin A content of the oil, and whether the manufacturer adds additional Vitamin A to the natural Vitamin A in the oil, but I feel I benefit greatly from Cod Liver Oil supplementation.
I take a separate Vitamin D3 capsule along with my cod liver oil. I also take a Vitamin K2 capsule also to get the synergistic benefits of all three working together. My dental health has improved since I started taking these supplements in addition to eliminating grains from my diet which reduced my exposure to phytic acid.