Vitamin D & Insulin: A Question of Race?

Could it be that vitamin D intake is more important for people with an African American (AA) background than for their European American (EA) neighbors? This is exactly, what a study that was recently published in Nutrition&Metabolism (Alvarez. 2010) seems to suggest.

In 115 African American (AA) and 137 European American (EA) healthy, premenopausal women the scientists  determined with 4-day food records and assessed the individual insulin sensitivity indexes (SI), as well as the Homeostasis Model Assessment of Insulin Resistance (HOMA-IR) values. The results are quite unequivocal:

Vitamin D intake was positively associated with SI (standardized β = 0.18, P = 0.05) and inversely associated with HOMA-IR (standardized β = -0.26, P = 0.007) in AA, and the relationships were independent of age, total body fat, energy intake, and % kcal from fat. Vitamin D intake was not significantly associated with indices of insulin sensitivity/resistance in EA (standardized β = 0.03, P = 0.74 and standardized β = 0.02, P = 0.85 for SI
and HOMA-IR, respectively). Similar to vitamin D, dietary calcium was associated with SI
and HOMA-IR among AA but not EA.

While the scientists refrain from premature speculation about the underlying reasons of the observed discrepancy, they highlight the importance of both, adequate vitamin D, as well as dietary calcium consumption for premenopausal women of African American descent. What I consider noteworthy is the fact that the mean vitamin D intake of both groups was way beyond even the currently suggested 400IU (most experts already suggest 1.000-2.000 IU per day). With a mean vitamin D intake of 111.5IU and 133.7IU per day. All subjects carry the risk of being "vitamin D deficient" and this is where increased intake may produce significant positive effects on various health marker (cf. More on Vitamin D).