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least in the more northern parts of the United States, mean serum 25OHD levels hovered around 40 nmol/L, consistent with an EAR intake. Further, this adjustment over-corrects because for persons living in southern parts of the United States—where NHANES generally is conducted during the winter months—their serum 25OHD levels are already reflective of winter and are not appropriately corrected from a summer level to a winter level. In the case of data for Canada from the CHMS, the mean serum 25OHD levels for all life stage groups are at or above 60 nmol/L. The fact that they are higher than those for the U.S. population may be in part a function of differences in the assay methods used, although this is not clearly established. If it is assumed that the Canadian values would be 8 percent lower if analyzed using the same methodology that was used in the U.S. survey, then they would then be quite similar to those for the United States, leaving open the question of whether the latitude difference between the two countries has a meaningful impact on serum 25OHD levels.


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