thought i would spend a few minutes on safe dosages of vitamin a (retinol).
my pills contain 10,000 IU of retinol as vit a palmitate. i started looking for studies and ended up finding mg units instead of IU.
10,000 IU vit A palmitate converts to 5500 mcg retinol. that would be 5.5mg.
Water-miscible, emulsified, and solid forms of retinol supplements are more toxic than oil-based preparations (2003)http://ajcn.nutrition.org/content/78/6/1152.short
"Chronic hypervitaminosis A is induced after daily doses of 2 mg retinol/kg in oil-based preparations for many months or years. In contrast, doses as low as 0.2 mg retinol · kg−1 · d−1 in water-miscible, emulsified, and solid preparations for only a few weeks caused chronic hypervitaminosis A. Thus, water-miscible, emulsified, and solid preparations of retinol are ≈10 times as toxic as are oil-based retinol preparations. The safe upper single dose of retinol in oil or liver seems to be ≈4–6 mg/kg body wt. These thresholds do not vary considerably with age."
The acute and chronic toxic effects of vitamin Ahttp://ajcn.nutrition.org/content/83/2/191.full
"Emerging evidence suggests that subtoxicity without clinical signs of toxicity may be a growing concern, because intake from preformed sources of vitamin A often exceeds the recommended dietary allowances (RDA) for adults, especially in developed countries. Osteoporosis and hip fracture are associated with preformed vitamin A intakes that are only twice the current RDA. Assessing vitamin A status in persons with subtoxicity or toxicity is complicated because serum retinol concentrations are nonsensitive indicators in this range of liver vitamin A reserves."
Vitamin Ahttp://lpi.oregonstate.edu/infocenter/v ... /vitaminA/
Generally, signs of toxicity are associated with long-term consumption of vitamin A in excess of ten times the RDA (8,000 to 10,000 mcg/day or 25,000 to 33,000 IU/day)... long-term intakes of preformed vitamin A in excess of 1,500 mcg/day (5,000 IU/day) are associated with increased risk of osteoporoticfracture and decreased BMD in older men and women (42-44). Although this level of intake is greater than the RDA of 700-900 mcg/day (2,300-3,000 IU/day), it is substantially lower than the UL of 3,000 mcg/day (10,000 IU/day). Only excess intakes of preformed vitamin A (retinol), not beta-carotene, were associated with adverse effects on bone health. Although these observational studies cannot provide the reason for the association between excess retinol intake and osteoporosis, limited experimental data suggest that excess retinol may stimulate bone resorption (45) or interfere with the ability of vitamin D to maintain calcium balance (46). In the U.S., retinol intakes in excess of 5,000 IU/day can be easily attained by those who regularly consume multivitamin supplements and/or fortified foods, including some breakfast cereals. At the other end of the spectrum, a significant number of elderly people have insufficient vitamin A intakes, which have also been associated with decreased BMD. One study of elderly men and women found that BMD was optimal at vitamin A intakes close to the RDA (43). Until supplements and fortified foods are reformulated to reflect the current RDA for vitamin A, it makes sense to look for multivitamin supplements that contain 2,500 IU of vitamin A or multivitamin supplements that contain 5,000 IU of vitamin A, of which at least 50% comes from beta-carotene (see example supplement label).