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Editor's Correspondence |

Vitamin D Supplements vs Plasma Level

John H. Glaser, MS
Arch Intern Med. 2009;169(16):1536. doi:10.1001/archinternmed.2009.280.
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Golomb et al1 suggest that calcium may have counteracted the effect of vitamin D in the Women's Health Initiative (WHI) study, as the reason for the calcium–vitamin D supplement showing no benefit against myocardial infarction, whereas Giovannucci et al2 found that higher plasma 25-hydroxyvitamin D concentrations lowered the risk of myocardial infarction in men.

An alternative explanation is that vitamin D supplements have a relatively small contribution to vitamin D plasma levels. Chiebowski et al3 found that many women who, before the WHI study, were ingesting the lowest level of vitamin D (diet plus supplements) had the highest plasma levels of vitamin D. The low correlation coefficient (r = 0.19) for supplements vs plasma levels shows that other factors such as sunlight exposure, body mass index, or genetic factors have a more significant effect on plasma levels. In fact, Chlebowski et al3 showed a similar contradiction as noted by Giovannucci et al2: plasma levels of vitamin D had no statistically significant effect on breast cancer, but the women who, before the WHI study, were ingesting the highest intake of vitamin D had an increased risk of breast cancer.

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