Reports of greater than expected vitamin D insufficiency coupled with emerging evidence that higher circulating concentrations of this nutrient may protect against cardiovascular disease have prompted a renewed interest in teasing out how environment, genetics, and behavior work independently and coordinately to influence vitamin D status. To help clarify this, researchers at Emory University studied vitamin D status in twins living in different North American locations.

"The results of the Karohl study are quite important," according to American Society for Nutrition Spokesperson Shelley McGuire, PhD. "Over the past couple decades, nutrition scientists have discovered that maintaining optimal vitamin D status is important for much more than keeping our bones strong. It's also critical for keeping our immune systems healthy and may help protect against diseases like heart disease and cancer. This study suggests that, whereas genetic differences impact winter vitamin D status, lifestyle choices and sun exposure (factors we can control) are predominant in the summer months. Additional research is still needed in more heterogeneous populations."

The authors concluded that during the winter vitamin D status is governed mainly by genetic factors. Conversely, non-genetic factors are most important during the summer. Future studies designed to better understand what these factors are will be especially useful as public health experts continue to explore ways to increase vitamin D status in different populations living under varying environmental and dietary situations.

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