Introduction: There is no comprehensive, systematic analysis of the vitamin D status of prisoners in the scientific literature.
Objective: To investigate the vitamin D status and its determinants in US prison inmates.
Hypothesis: Given the uniformity of dietary intake amongst inmates, vitamin D status will be determined by non-dietary factors such as skin pigmentation, security level-, and the duration of incarceration.
Subjects and methods: A retrospective study of 526 inmates (males, n=502, age 48.6 ± 12.5 years; females, n=24, age 44.1 ± 12.2) in Massachusetts prisons. Vitamin D sufficiency, insufficiency, and deficiency were respectively defined as a 25(OH)D concentration 75 nmol/L; 50 to 75 nmol/L; and <50 nmol/L. The Massachusetts Department of Correction Statement of Nutritional Adequacy stated that each inmate received the recommended daily allowance of vitamin D daily. Security level of incarceration was designated as minimum, medium, and maximum. Racial groups were categorized as Black, white, Asian, and Others.
Results: Serum 25(OH)D levels peaked in summer and autumn, and decreased in winter and spring. Vitamin D deficiency occurred in 50.5% of blacks, 29.3% of whites, and 14.3% of Asian inmates (p=0.007). Black inmates had significantly lower serum 25(OH)D level than white inmates at the maximum security level (p=0.015), medium security level (p=0.001), but not at the minimum security level (p=0.40). After adjusting for covariates black inmates at a maximum security level had a four-fold higher risk for vitamin D deficiency than white inmates at the same security level (OR 3.9 [95% CI 1.3-11.7].
Conclusions: The vitamin D status of prison inmates is determined by skin pigmentation, seasons, and the security level of incarceration.