Effect of Latitude on Vitamin D Levels

Vitamin D levels have been linked to bone health and to numerous diseases; however, an element that lacks substantial direct data and limits the evidence basis regarding whom to screen for vitamin D deficiency is the effect of latitude on vitamin D levels.

To determine whether latitude influences vitamin D levels and to investigate the influence of other factors that may affect vitamin D levels, including sex, race, skin type, and body mass index.

Osteopathic medical students were recruited from campuses in Bradenton, Florida, and Erie, Pennsylvania. Surveys were administered to obtain demographic information, and blood samples were drawn to measure total vitamin D levels. Two-sample t tests, Fisher exact test, and logistic regression was used to assess differences in total vitamin D levels between the 2 locations.

A total of 359 medical students (aged 22-57 years) were included in the study, 194 at the Bradenton campus and 214 at the Erie campus. The mean (SD) vitamin D level was 34.5 (11.8) ng/mL among participants in Bradenton and 28.1 (12.4) ng/mL among participants in Erie. Logistic regression models revealed an adjusted OR of 3.3 (95% CI, 1.73-6.4) for deficient total vitamin D among Erie students. Non-white race, male sex, and high body mass index were also statistically significant risk factors for vitamin D deficiency in regression models (P<.05).

Latitude was found to be a statistically significant risk factor for vitamin D deficiency. Additionally, the findings suggest that persons with darker skin tone and, to a lesser degree, men and persons who are overweight or obese are also at increased risk for vitamin D deficiency. Physicians should be cognizant of these risk factors when deciding whom to screen.