Has science proven that the minimal acceptable blood level of vitamin D, in the form of 25(OH)D, is above 50 ng/mL (125 nmol/L)? No. If you’ve been trying to maintain your levels this high because you thought this was the case, I’m sorry to break the news. There is, on the contrary, good evidence that 25(OH)D levels should be at least 30-35 ng/mL (75-88 nmol/L). Much higher levels may be better, or they could start causing harm, especially in the absence of adequate vitamins A and K2. Once we leave the land of 30-35 ng/mL, however, we enter the land of speculation.
This January, Dr. Linda Linday, a pediatrician who researches cod liver oil, Michael F. Holick, MD PhD, and several other researchers defended cod liver oil against criticism made a year earlier by Dr. Cannell of the Vitamin D Council and 16 other researchers.
They cite the WAPF December 2008 "Cod Liver Oil Update" as an example of the importance of the vitamin A-to-D ratio emerging in the online supplement and nutrition newsletter communities. This update was based largely on the work I have done for WAPF on the fat-soluble vtamins. They suggest the optimal ratio is between four and eight, in IUs.