11
Calcium regulation in the human body.[1] The role of vitamin D is shown in orange.
A Toronto study concluded, "skin pigmentation, assessed by measuring skin melanin content, showed an inverse relationship with serum 25(OH)D". The uniform occurrence of low serum 25(OH)D in Indians living in India. and Chinese in China, does not support the hypothesis that the low levels seen in the more pigmented are due to lack of synthesis from the sun at higher latitudes; the leader of the study has urged dark-skinned immigrants to take vitamin D supplements nonetheless, saying, "I see no risk, no downside, there's only a potential benefit". Whether the toxicity of oral intake of vitamin D is due to that route being unnatural, as suggested by Fraser, is not known, but there is evidence to suggest that dietary vitamin D may be carried by lipoprotein particles into cells of the artery wall and atherosclerotic plaque, where it may be converted to active form by monocyte-macrophages. These findings raise questions regarding the effects of vitamin D intake on atherosclerotic calcification and cardiovascular risk. VDR ligands have been shown to increase the activity of natural killer cells, and enhance the phagocytic activity of macrophages. Active vitamin D hormone also increases the production of cathelicidin, an antimicrobial peptide that is produced in macrophages triggered by bacteria, viruses, and fungi. Suggestions of a link between vitamin D and the onset of multiple sclerosis posited
Health effects
Immune system
that this is due to the immune-response suppression properties of Vitamin D and that vitamin D is required to activate a histocompatibility gene (HLA-DRB1*1501) necessary for differentiating between self and foreign proteins in a subgroup of individuals genetically predisposed to MS. Whether vitamin D supplements during pregnancy can lessen the likelihood of the child developing MS later in life is not known; however, vitamin D fortification has been suggested to have caused a pandemic of allergic disease and an association between vitamin D supplementation in infancy and an increased risk of atopy and allergic rhinitis later in life has been found . Veteran vitamin D researcher Hector DeLuca has cast doubt on whether vitamin D affects MS. Lack of vitamin D synthesis is a possible explanation for high rates of